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Domains Definition Domains are specific areas on a protein usually divided on the linear sequence which have different functions. Usually between 50-150 amino acids but can be as big as 250 amino acids 
What are the three domains to the lac repressor ?&nbsp;"<img src=""paste-86722420a0b8145ee148957759b9569884e19540.jpg"" width=""554""><br><ul><li>(a) Green - the tetramerization domain which acts as a protein-protein interaction domain&nbsp;</li><li>(b) Orange - Regulatory domain that binds to allolactose ot IPTG =.&nbsp;</li><li>(c) DNA binding domain - specifically recognizes a DNA sequence for binding via an HTH (helix -turn-helix) motif&nbsp;</li><li>A linker domain connects a and c&nbsp;</li></ul>"
Do domains have to be contigous ?"No. Contigous domains are domains where the AA are next to eachother in the linear seqeunce - typiclaly forms a continious stretch of amino acids. Alanine racemase has one of its domains interrupted by an additional sequence shown in gree. This is a domain that is not on a contiguous seqeuence.&nbsp;<br><img src=""paste-ff7f2b05865f3a6f12620627fe71d9e86fb422f2.jpg"">"
At what size limit does proteins contain only a single functional domain and is usually globular ?30KDa&nbsp;
"How do protein domains interact functionally, and what is an example of domain ""cross talk""?""<div>Each domain carries out a separate function, but they often communicate; binding or catalysis in one domain can affect the other.<br>
<strong>Example:</strong> In the <strong>lac repressor</strong>, IPTG binding induces a conformational change that forms a tetramer unable to bind DNA, leading to <strong>operon expression</strong>.</div>"
What structural features allow domains to fold independently, and can they function when separated?"<div><strong>A:</strong> Domains have <strong>hydrophobic cores</strong> that help them fold into distinct structures. Some domains, like the <strong>RNA-binding domain of Rho</strong>, remain functional even when separated.<br>
However, others—like the <strong>ATPase domain of Rho</strong>—require interaction (e.g., RNA binding) to become active.</div>"
What is the likely evolutionary origin of multi-domain proteins?Multi-domain proteins likely evolved through <strong>gene fusion events</strong>, where genes that once coded for separate proteins combined. This results in proteins with <strong>structurally similar domains</strong> performing related or complementary functions.&nbsp;<br><ul><li>Domain structurea form seperate function by reporoducing and copying domains and one domain is free to mutate to give different function&nbsp;</li></ul>
What evidence supports the idea that multi-domain proteins evolved from gene duplication or fusion?"<div>Structural similarities across domains—such as in <strong>thioesterase</strong> (b- two fused domains) and <strong>thioester dehydrase</strong> (a-two identical subunits)—show nearly <strong>superimposable backbones</strong>, differing mostly in loops and connectors. This suggests a <strong>common ancestral origin</strong>.</div><div><img src=""paste-8f7f86b6afe6a15647c670df32b364945a3a7062.jpg""><br></div>
<div></div>"
How does gamma crystallin illustrate gene duplication in protein evolution?"<strong>Gamma crystallin</strong>, a lens protein, has <strong>two nearly identical domains</strong>, each made up of <strong>two similar halves</strong>. This likely arose from <strong>internal gene duplications</strong>, supported by their <strong>~40% sequence identity</strong>—a hallmark of shared ancestr<br><br><img src=""paste-2b879b2af72922d4be24fe5651d8f4d69cc8f02f.jpg"">"
How does the structure of mouse β-crystallin support the theory of exon shuffling in protein evolution?<div>&nbsp;The <strong>mouse β-crystallin gene</strong> is divided into <strong>four exons</strong>, each coding for a <strong>four-stranded β-sheet domain</strong>. These exons align with the <strong>junctions between domains</strong>, providing strong evidence for <strong>exon shuffling</strong>—a mechanism that rearranges coding segments to create new domain combinations and diversify proteins.</div>
How do multi-domain proteins evolve increased functionality through gene duplication and exon fusion?<strong>Gene duplication</strong> allows each domain to follow its <strong>own evolutionary path</strong>, enabling functional diversification. Additionally, <strong>tandem fusion of unrelated exons</strong> from different genes can form new multi-domain proteins with <strong>specialized, novel functions</strong>, contributing to evolutionary innovation.
Which part of signaling pathways are not conserved vs mainly conserved?"Not conserved- Ligand binding to receptor - there are a lot of this&nbsp;<br>Conserved - The main signaling pathways contain highly conserved domains involved in recognition, signaling and sensing&nbsp;<br><ul><li><div><strong>SH3 domains</strong> bind <strong>proline-rich regions</strong></div>
</li><li>
<div><strong>SH2 domains</strong> bind <strong>phosphotyrosine-containing sequences</strong></div>
</li><li>
<div><strong>PH domains</strong> (pleckstrin homology) bind <strong>membranes</strong></div>
</li><li>
<div><strong>PTPase</strong> is a <strong>phosphatase domain</strong></div>
</li><li>
<div><strong>Kinase</strong> is a <strong>protein kinase domain</strong></div>
</li><li>
<div><strong>G-kinase</strong> refers to <strong>guanylate kinase activity</strong></div>
</li><li>
<div><strong>PLC domain</strong> is the <strong>catalytic region of phospholipase C</strong></div></li></ul>
"
How is tertiary protein structure related to domains?&nbsp;"There is a <strong>limited set of protein folds</strong>, and many new structures are variations of existing ones. A protein’s <strong>tertiary structure</strong> depends on the <strong>number of domains</strong> and how they <strong>interact after being joined</strong>.<br>
Proteins are grouped into <strong>families</strong> based on the <strong>domains they contain</strong>, reflecting <strong>evolutionary relationships</strong>."
What are Motifs?Motifs can be defined as a common secondary structure elements or identified by a defined sequence.&nbsp;
What is the CXXC-X12-HXXXH motif ?"<img src=""paste-7b6a62c828a7cbadeba6187bf7859981c14b3a4f.jpg"" style=""float: left;"">This motif defines a <strong>zinc finger</strong>, a <strong>functional motif</strong> characterized by the sequence:&nbsp;<strong>CXX(XX)CXXXXXXXXXXXXHXXXH</strong><br><ul><li>It binds a <strong>zinc ion</strong>, which <strong>stabilizes</strong> the structure by coordinating with the cysteine and histidine residues, forming a <strong>12-residue loop</strong>.</li></ul>The motif can often be identified by simple <strong>sequence inspection</strong> and is commonly found in <strong>DNA-binding proteins</strong>, helping them recognize and bind specific sequences.<br>
"
Function and examples of the helix-turn-helix motif?"The <strong>helix-turn-helix (HTH)</strong> motif is a structural motif that binds <strong>DNA</strong>. It is found in many <strong>DNA-binding enzymes</strong> such as <strong>restriction enzymes</strong>. The <strong>interacting helix</strong> samples the <strong>DNA sequence</strong> by probing the <strong>major groove</strong>. In the case of the <strong>lambda phage repressor CI</strong>, two <strong>HTH motifs</strong> work together to bind DNA, allowing the protein to <strong>dictate sequence specificity</strong> through these interactions.<br><img src=""paste-5e90862a63e463f4b06ae26e1db58812a685f05a.jpg"">"
What type of motif is found in many hormones?"<div>Functional motifs like the
four-helix bundle mutually antiparallel helices are found in many
hormones.&nbsp; The amino acids are vastly
different, but the structure can have many different activities. Human growth
hormone is seen below</div><div><br></div><div style=""text-align: center; ""><img src=""paste-ecea2d28014cf92ba6ab575b727c01714d7f5afd.jpg""><br></div>"
What is an example of <strong>functional convergence</strong> in proteins, and how does it relate to their structures?"<div><strong>Convergence</strong> refers to different structures evolving to perform the same function.<br>
<strong>Example:</strong> <strong>Subtilisin</strong> and <strong>chymotrypsin</strong> are both <strong>serine proteases</strong> with a <strong>catalytic triad</strong> consisting of <strong>aspartic acid, histidine</strong>, and <strong>serine</strong>, performing the same chemical reaction (<strong>hydrolysis of a peptide bond</strong>). Despite their <strong>structural differences</strong>, they achieve the same function, illustrating <strong>functional convergence</strong>—the same function with distinct structural solutions.</div><div><img src=""paste-69b834c7a29408ebcd1dcb440e865a15e0a7db44.jpg""><br></div>"
What is motif divergence and provide exapmple?"<strong>Divergence</strong> refers to the evolution of different functions or activities from a similar structural motif.<br>
<strong>Example:</strong> <strong>Triose phosphate isomerase (TIM)</strong> and <strong>alanine racemase</strong> both share the same <strong>TIM-barrel structure</strong>, but <strong>alanine racemase</strong> has a <strong>large interruption</strong> in the barrel. While the overall structure is similar, <strong>alanine racemase</strong> has a different set of <strong>amino acids</strong> and performs a <strong>distinct function</strong>, illustrating <strong>motif divergence</strong>—similar structures, but different activities.<br><img src=""paste-3cd15675b4597957d1b312fc48e59849e444c0f9.jpg"">"
"<div>What are the key characteristics of Beta domains, and what is the odd-strand rule?</div>
<div></div>""<ul><li>Beta domains are built from beta sheets, tight turns, and irregular loops. They always have antiparallel B sheets with no helices between the beta sheets&nbsp;</li><li>Odd-Strand Rule: A β-strand is connected to either the <strong>next (1 strand away)</strong> or the <strong>third (3 strands away)</strong> strand.&nbsp;</li><li>Connecting to the next strand creates an up and down motif</li></ul><div><img src=""paste-6ca64d0cadc40e30fe01080adf818892821df3a7.jpg""><br></div>"
Explain structure of the greek key motif&nbsp;"<ul><li>Greek key motif consists of antiparallael strands , where the first 3 strands are adjacent but the 4th strand is adjacent to the 1st with a long colecting loop to the 5th.&nbsp;</li><li>This is seen by one of the two subunits of pre-albumin&nbsp;</li><li><img src=""paste-214ddf59f5d493bec6f0947616dc62d26163016f.jpg""><br></li></ul>"
What is the jelly-roll motif ?"A beta sandwich built from two sheets with topologies resembling a greek key design. The sheets pack almost at a right angle of each other.&nbsp;<br><img src=""paste-c255840c754c42c7f8230693b2a3e248402add44.jpg"">"
"What is the motif and function of the following protein ? What could be the reason behind the structure? Protein is bacteriochlorophyll A&nbsp;<br><img src=""paste-c255840c754c42c7f8230693b2a3e248402add44.jpg"">"This is the jelly-roll motif and the structure allows for the rapid resonance enrgy transfer between chlorophyll molecules by ollowing them to be close to eachother. Overall this helly roll motif allows for rapid communication between chlorophyll groups.&nbsp;
"<div>How are parallel β-sheets connected, and what is the structural bias in crossover direction?</div>
<div></div>""<ul><li><div><strong>Parallel β-sheets</strong> require <strong>intervening segments</strong> to connect strands—usually <strong>α-helices</strong>.</div>
</li>
<li>
<div>These connections involve <strong>crossovers</strong> between strands:</div>
<ul>
<li>
<div><strong>Right-handed crossover (b)</strong>: Preferred; seen in <strong>~95%</strong> of α/β structures.</div>
</li>
<li>
<div><strong>Left-handed crossover (a)</strong>: Rare.</div>
</li>
</ul>
</li>
<li>
<div>The right handed twist results in a large bias
towards the right handed crossover and is seen in 95% of the
alpha/beta structures.</div></li><li><div><img src=""paste-6cdf667efb3c34dc6866e4ba10afda0262280763.jpg"">&nbsp;</div></li></ul>"
"<div>What are the two major α/β structural folds?&nbsp;</div>
<div></div>""<ul><li><div><strong>lpha/Beta (α/β) structures</strong> consist of <strong>alternating β-strands and α-helices</strong>.</div>
</li>
<li>
<div>Two major types:</div>
<ul>
<li>
<div><strong>TIM barrel</strong>: 8 repeating α/β units forming a closed barrel (seen in ~10% of all proteins).</div>
</li>
<li>
<div><strong>α/β twist</strong>: Seen in enzymes like <strong>Aspartate semi-aldehyde dehydrogenase</strong>.</div>
</li>
</ul>
</li>
<li>
<div>When the α/β motif is <strong>repeated 8 times</strong>, it forms a <strong>highly stable TIM barrel</strong> structure.</div>
</li>
<li>
<div>TIM barrels are among the <strong>most common and versatile</strong> protein folds.</div></li></ul><div><img src=""paste-65530395620277430e9173dc4c4a873dd4fcf852.jpg"" width=""426""><br></div>"
"<div>What is the structure and function of the α/β twist in DNA-binding proteins?</div>
<div></div>""<ul><li><div>The <strong>parallel β-strands</strong> form an <strong>open, saddle-shaped twist</strong> (not a closed barrel).&nbsp;<strong>Sheets are non-consecutive</strong>: the first strand is centrally located, forming one half of the structure, and additional strands radiate outward.</div></li><li>
<div><strong>α-helices</strong> lie on one side, starting from the opposite half of the sheet.</div>
</li><li>
<div><strong>Function:</strong> Seen in <strong>TATA-box binding proteins</strong>, this motif binds the <strong>minor groove</strong> of DNA and causes <strong>significant bending</strong> of the DNA strand.</div></li></ul><div><img src=""paste-5055751affdf02100914d26707e603495c0bc345.jpg"" width=""654""><br></div>
"
"<div>What defines the α + β class of proteins?</div>
<div></div>""<ul><li><div>Contains <strong>independent α-helices and β-sheets</strong> that <strong>do not alternate</strong> in sequence.</div>
</li>
<li>
<div><strong>No universal folding principle</strong>—arrangement varies.</div>
</li>
<li>
<div><strong>Helices may pack against sheets</strong>, and:</div>
</li><ul>
<li>
<div><strong>Back side of β-sheets</strong> may be <strong>solvent-exposed</strong>, or</div>
</li>
<li>
<div><strong>Helix layers</strong> can form <strong>functional grooves</strong>, such as the <strong>peptide-binding groove</strong> in the <strong>MHC (major histocompatibility complex)</strong>.</div>
</li>
</ul>
</ul><div><img src=""paste-da961542da94db41e0a73a997bc59503f7cf9569.jpg"" width=""624""><br></div>"
"<div>How are small, irregular proteins stabilized structurally?</div>
<div></div>""<ul><li><div>Many small proteins <strong>lack a hydrophobic core</strong> for stabilization.</div>
</li>
<li>
<div>They are stabilized by:</div>
<ul>
<li>
<div><strong>Disulfide bonds</strong> (e.g., in <strong>scorpion toxin</strong>, <strong>snail venom</strong>, <strong>ragweed allergen</strong>, <strong>protease inhibitors</strong>).</div>
</li>
<li>
<div><strong>Metal ions</strong> (e.g., <strong>zinc fingers</strong> use zinc coordination for structure).</div>
</li>
</ul>
</li>
<li>
<div>These features allow for <strong>compact and functional</strong> protein folds in otherwise unstable sizes.</div></li></ul><div><img src=""paste-38bd5b18ac3441232c6398d2b57767447bb4f131.jpg"" width=""643""><br></div>"
"<div>What are the basic principles of protein quaternary structure and how are subunit compositions represented?</div>
<div></div>""<ul><li><div><strong>Quaternary structure</strong> involves proteins forming <strong>complexes</strong> with one or more polypeptide chains.</div>
</li>
<li>
<div>Subunits can be:</div>
<ul>
<li>
<div><strong>Identical</strong> → <em>Homodimers</em>, <em>homotetramers</em> (e.g., <em>(aa)</em>, <em>(a4)</em>)</div>
</li>
<li>
<div><strong>Different</strong> → <em>Heterodimers</em>, <em>heteropentamers</em> (e.g., <em>(ab)</em>, <em>(a2bcd)</em>)</div>
</li>
</ul>
</li>
<li>
<div>Examples:</div>
<ul>
<li>
<div><em>(a2b2)</em> = <strong>Hemoglobin</strong>, a heterotetramer of α and β chains</div>
</li>
<li>
<div><em>(a2bcd)</em> = <strong>Acetylcholine receptor</strong>, four different subunits</div>
</li>
</ul>
</li>
<li>
<div>This notation reflects both <strong>composition</strong> and <strong>stoichiometry</strong>.</div>
</li></ul>"
"<div>What determines specificity and evolutionary patterns in quaternary protein complexes?</div>
<div></div>""<ul><li><div>Subunits may be:</div>
<ul>
<li>
<div><strong>Structurally similar</strong>, indicating a <strong>shared evolutionary origin</strong></div>
</li>
<li>
<div><strong>Structurally distinct</strong>, as seen in <strong>cytochrome bc1</strong> complex</div>
</li>
</ul>
</li><li>
<div>Some assemblies include <strong>mixed subunits</strong> (e.g., <strong>RNA polymerase</strong>, <strong>F1-ATP synthase</strong>)</div>
</li><li>
<div>Interactions are <strong>highly specific</strong>:</div>
<ul>
<li>
<div>Subunits form <strong>tight, exclusive interactions</strong>—<strong>no random swapping</strong></div>
</li>
<li>
<div>Example:</div>
<ul>
<li>
<div><strong>F1-ATP synthase</strong> <em>(a3b3c)</em> and <strong>Rho factor</strong> <em>(a6)</em> share similar folds but <strong>do not exchange subunits</strong></div></li></ul></li></ul></li></ul>
"
"<div>What defines complementarity between two protein binding partners?</div>
<div></div>""<div><strong>Complementarity</strong> maximizes <strong>weak binding interactions</strong>, including:</div>
<ul><li><strong>Shape complementarity</strong> (lock-and-key fit)</li>
<li>
<div><strong>Electrostatic attractions</strong>: (+) to (−) charges</div>
</li>
<li>
<div><strong>Hydrogen bonding</strong>: e.g., Ser/Thr ↔ Gln/Asn</div>
</li>
<li><strong>Van der Waals</strong> contacts between closely packed residues</li></ul>"
"What is the structural difference between reversable and bound interfaces between subunits when forming quaternary
structure?&nbsp;""<ul><li><div><strong>Reversible interfaces</strong> have <strong>smaller, less tightly packed surfaces</strong> with moderate shape complementarity and rely on <strong>weak non-covalent interactions</strong> (e.g., hydrogen bonds, electrostatics), allowing <strong>transient associations</strong>.</div>
</li><li>
<div><strong>Permanently bound interfaces</strong> have <strong>larger, highly complementary surfaces</strong> with extensive <strong>hydrophobic packing and specific interactions</strong>, resulting in <strong>stable, long-term subunit assembly</strong>.</div></li></ul>
"
What is the most studied hydrophobic complemntary between two binding subunits/partners?&nbsp;"<ul><li><div><strong>Coiled-coil dimers</strong> involve <strong>two α-helices</strong> interacting via hydrophobic side chains</div></li><li>
<div>These <strong>hydrophobic stripes</strong> form a <strong>twisted coil</strong>, stabilizing the dimer.</div>
</li><li>
<div><strong>Structure prediction</strong> is possible from <strong>sequence patterns</strong> due to this repeat.</div></li></ul><div><img src=""paste-307e96252a76e8125dcc86ab55f208be7f72deed.jpg"" width=""647""><br></div>
"
What sequence pattern allows for coiled-coil dimers?&nbsp;"<ul><li><div><strong>Hydrophobic residues (e.g., leucine)</strong>&nbsp;are placed at regular intervals — every&nbsp;<strong>7 residues</strong>.</div></li><ul><li><div>This is called a&nbsp;<strong>heptad repeat</strong>&nbsp;(abcdefg), with&nbsp;<strong>positions a and d</strong>&nbsp;typically hydrophobic</div></li></ul></ul><div><img alt=""Protein folding 04: Formation of alpha helices"" src=""heptad-repeat.png""><br></div>"
Whata are three different ways surface complementarity occurs?"<div><ul><li><div><strong>Preformed (Lock-and-Key):</strong> Complementary surfaces exist <strong>before binding</strong>, allowing direct interaction.</div>
</li><li>
<div><strong>Induced Fit:</strong> Binding causes <strong>conformational changes</strong> that <strong>expose or reshape</strong> interaction surfaces.</div>
</li><li>
<div><strong>Mutual Conformational Change:</strong> <strong>Both proteins undergo structural adjustments</strong> over time until complementarity is achieved.</div></li></ul>
</div>"
"<div>What are four major DNA-binding motifs and their structural characteristics?</div>
<div></div>""<ol><li><div><strong>Zinc Finger Motif</strong></div>
<ul>
<li>
<div>Uses a <strong>zinc ion</strong> to stabilize the fold.</div>
</li>
<li>
<div>Features <strong>α-helix and β-sheet elements</strong> that interact with the <strong>major groove</strong> of DNA.</div>
</li>
<li>
<div>Found in many&nbsp; transcription factors.</div>
</li>
</ul>
</li>
<li>
<div><strong>Helix-Turn-Helix (HTH) Motif</strong></div>
<ul>
<li>
<div>Consists of <strong>two α-helices</strong> joined by a <strong>short turn</strong>.</div>
</li>
<li>
<div>One helix (recognition helix) fits into the <strong>major groove</strong> of DNA.</div>
</li>
<li>
<div>Found in <strong>restriction enzymes</strong>, <strong>lambda repressor CI</strong>, and <strong>lac repressor</strong>.</div>
</li>
</ul>
</li>
<li>
<div><strong>Saddle Motif (from α/β twist)</strong></div>
<ul>
<li>
<div>Forms a <strong>saddle-like shape</strong> with <strong>parallel β-sheets and α-helices on one side</strong>.</div>
</li>
<li>
<div>Seen in the <strong>TATA-binding protein</strong>, which binds the <strong>minor groove</strong> of DNA and bends it significantly.</div>
</li>
</ul>
</li>
<li>
<div><strong>Leucine Zipper Motif</strong></div>
<ul>
<li>
<div>Contains a <strong>heptad repeat</strong> (leucine every 7 residues) forming a <strong>coiled-coil dimer</strong>.</div>
</li>
<li>
<div>Facilitates <strong>dimerization</strong> and positions adjacent <strong>DNA-binding domains</strong>.</div>
</li>
<li>
<div>Often involved in <strong>transcriptional regulation</strong>.</div>
</li>
</ul>
</li></ol>"
"<div>How does a mutation in hemoglobin lead to sickle-cell anemia?</div>
<div></div>""<ul><li><div>A <strong>hydrophobic mutation</strong> (Asp → Val at position 8 in β-hemoglobin) increases <strong>hydrophobic surface area</strong>.</div>
</li>
<li>
<div>This promotes <strong>abnormal hemoglobin polymerization</strong> in the <strong>deoxy state</strong>.</div>
</li>
<li>
<div>Results in <strong>distorted, sickle-shaped red blood cells</strong>.</div>
</li>
<li>
<div>These cells have <strong>poor capillary flow</strong>, leading to <strong>blockages and tissue damage</strong>.</div>
</li></ul>"
"<div>What is a dominant-negative mutation in a multisubunit protein?</div>
<div></div>""<ul><li><div>A mutation in <strong>one subunit</strong> can create a defective protein that still <strong>binds</strong> but lacks <strong>catalytic activity</strong>.</div>
</li><li>
<div>This inactive subunit <strong>competes</strong> with functional ones, interfering with the entire complex.</div>
</li><li>
<div>The <strong>mutant protein accumulates</strong>, especially if expression is <strong>upregulated due to loss of function</strong>.</div>
</li><li>
<div>This causes a <strong>dominant-negative phenotype</strong>, even though only one allele is mutated.</div></li></ul>
"
"<div>How do mutations differ in impact between single-subunit and multisubunit enzymes?</div>
<div></div>""<ul><li><div>In <strong>single-subunit enzymes</strong>, a mutation in one allele usually leads to <strong>loss of function</strong>, but the <strong>second (wild-type) allele compensates</strong>, making the mutation <strong>recessive</strong>.</div>
</li>
<li>
<div>In <strong>multisubunit proteins</strong>, one defective subunit can impair the entire complex, leading to <strong>dominant-negative effects</strong>.</div>
</li>
<li>
<div>This occurs because the <strong>defective protein integrates</strong> into the complex but <strong>disrupts function</strong>.</div>
</li></ul>"
"<div>How do subunit interactions influence symmetry in protein assemblies?</div>
<div></div>""<ul><li><div><strong>Identical subunits</strong> form <strong>symmetric assemblies</strong>, while <strong>different subunits</strong> often create <strong>asymmetric complexes</strong> (e.g., human growth hormone bound by two receptor monomers).</div>
</li><li>
<div><strong>Asymmetric protomers</strong> with complementary surfaces (A and A′) can form:</div>
<ul>
<li>
<div><strong>Dimers</strong> if A and A′ share the same edge.</div>
</li>
<li>
<div><strong>Tetramers</strong> if A and A′ are on <strong>different faces</strong> (e.g., 90° apart).</div>
</li>
</ul>
</li><li>
<div>Additional binding sites (B and B′) allow for <strong>higher-order assemblies</strong>.</div></li></ul><div><img src=""paste-57c7bbf23e139c12a86a0b5c1f1e200c8abc42d4.jpg""><br></div>
"
PseudosymmetrySymmetric structures formed by <strong>closely related but non-identical subunits</strong>, as seen in <strong>hemoglobin</strong>.
"<div>How do protein motions vary in scale and time, and why is this flexibility important?</div>
<div></div>""<ul><li><div>Proteins exhibit <strong>flexibility</strong> on different <strong>time and length scales</strong>:</div>
<ul>
<li>
<div><strong>Atomic vibrations</strong> (≤1 Å) occur in <strong>femto- to picoseconds</strong>.</div>
</li>
<li>
<div><strong>Hinge bends and ring flips</strong> (up to 5 Å) occur in <strong>nano- to milliseconds</strong>.</div>
</li>
<li>
<div><strong>Triggered conformational changes</strong> (up to 30 Å+) occur over longer timescales.</div>
</li>
</ul>
</li><li>
<div><strong>Example:</strong> TIM enzyme shows a <strong>large domain movement</strong>—a flexible lid covers the active site upon substrate binding to block solvent.</div>
</li><li>
<div><strong>Myoglobin</strong> shows that <strong>core residues are rigid</strong>, while <strong>surface residues vary in flexibility</strong>, aiding function and interaction.</div></li></ul>
"
"<div>How do protein dynamics and induced fit contribute to enzymatic function?</div>
<div></div>""<ul><li><div>Proteins are <strong>semi-liquid</strong>: more flexible than crystals but less than water.</div>
</li><li>
<div>Motions like <strong>aromatic residue flipping</strong> are rare and require <strong>coordinated movement</strong> of nearby atoms—<strong>improbable but possible</strong> (~1000 flips/sec).</div>
</li><li>
<div><strong>Lysozyme</strong> has <strong>two stable conformations</strong> separated by an energy barrier—only one is <strong>biologically active</strong>.</div>
</li><li>
<div><strong>Induced fit</strong> allows proteins to switch to an active form <strong>only upon substrate binding</strong>, preventing <strong>unwanted catalysis</strong> (e.g., <strong>hexokinase</strong> does not hydrolyze ATP without glucose).</div></li></ul>
"
"<div>What makes the microenvironment of an
active site different from the bulk solvent?</div>""<div>•<span style=""font-weight: bold;"">Active
sites</span> are <span style=""font-weight: bold;"">ligand-binding
regions</span> that
catalyze chemical reactions.</div>
<div>•They
form a <span style=""font-weight: bold;"">three-dimensional
cavity</span> with
<span style=""font-weight: bold;"">loosely
packed side chains</span>,
resembling a <span style=""font-weight: bold;"">nonpolar organic solvent</span> more
than water.</div>
<div>•<span style=""font-weight: bold;"">Electrostatic
interactions</span>
are <span style=""font-weight: bold;"">stronger</span> due
to the <span style=""font-weight: bold;"">low
dielectric constant</span>
(minimal shielding).</div>
<div>•<span style=""font-weight: bold;"">Favorable
interactions</span>
dominate, allowing strong binding—even if a few <span style=""font-weight: bold;"">unfavorable contacts</span>
(like charge crowding) are present.</div>"
"How
do enzymes promote general acid-base catalysis differently than in aqueous
solution?""In
<span style=""font-weight: bold;"">aqueous
solution</span>, an
acid (e.g., Glu) would readily protonate a nearby base (e.g., Lys),
neutralizing both and preventing catalysis.In a <span style=""font-weight: bold;"">protein’s
nonpolar microenvironment</span>,
proximity of acid and base is maintained <span style=""font-weight: bold;"">without spontaneous proton </span><span style=""font-weight: bold;"">transfer</span>.This
special environment allows <span style=""font-weight: bold;"">both groups to remain chemically
active</span> for
catalysis"
"<div>How does aspartate aminotransferase
illustrate control of acid-base chemistry in enzymes?</div>""<div><ul><li>In <span style=""font-weight: bold;"">aspartate
aminotransferase</span>,
<span style=""font-weight: bold;"">Glu</span> and <span style=""font-weight: bold;"">Lys</span>
residues bind the <span style=""font-weight: bold;"">pyridoxal phosphate (PLP) cofactor</span>.</li><li>Their
<span style=""font-weight: bold;"">proton
affinities are altered</span>
by the protein environment:</li><li><span style=""font-weight: bold;"">Glu remains protonated</span>
(acidic form).</li><li><span style=""font-weight: bold;"">Lys remains unprotonated</span>
(basic form).</li><li>This
allows <span style=""font-weight: bold;"">acid
and base</span> to
exist <span style=""font-weight: bold;"">side-by-side</span>
without neutralizing each other, supporting efficient catalysis.</li></ul></div>
"
"<div>How do proteins alter proton affinity to
enable base catalysis?</div>""<div></div>
<div><ul><li>Proteins
can <span style=""font-weight: bold;"">lower
the </span><span style=""font-weight: bold;"">pKa</span> of
functional groups like <span style=""font-weight: bold;"">lysine</span> by: Placing two <span style=""font-weight: bold;"">lysines</span><span style=""font-weight: bold;"">
close together</span>
(electrostatic repulsion lowers proton affinity).</li><li><span style=""font-weight: bold;"">Burying lysine</span> in a
<span style=""font-weight: bold;"">hydrophobic
pocket</span>,
where protonation is unfavorable due to the <span style=""font-weight: bold;"">low dielectric constant</span>.</li><li>This
allows lysine to act as a <span style=""font-weight: bold;"">general base</span> at
lower pH by staying <span style=""font-weight: bold;"">unprotonated</span>.</li><li><span style=""font-weight: bold;"">Example</span>: In <span style=""font-weight: bold;"">mandelate
racemase</span>, <span style=""font-weight: bold;"">K166</span>
functions as a <span style=""font-weight: bold;"">general base</span> and <span style=""font-weight: bold;"">proton
shuttle</span>,
aided by a <span style=""font-weight: bold;"">Mg²⁺
ion</span> that
stabilizes substrate and shapes the <span style=""font-weight: bold;"">active site geometry</span>.</li></ul><div><img src=""paste-fc660541f11530d79623e4eaa76b2dd05ddff40d.jpg""><br></div></div>
"
"<div>What is important when designing
inhibitors?&nbsp;</div>""<div>You have to design them with great affinity to the
target active site, but cant be
too acurate
because it can interfere with required enzymes and mess with biological
processes. Example is targeting HIV protease, keeping in mind not to affect the
naturally occurring proteases.&nbsp;</div>"
"What
does the thermostability of proteins indicate about important properties
required for function?&nbsp;""We
see that at lower temps than at the activation temp profile, proteins are too
RIGID for function whereas correct temperature allows for flexibility and thus
the catalytic function of the protein<br><img src=""paste-943988402d89f159051bcca1f0b5d5f7ae72ae2f.jpg""><br>&nbsp;"
"<div>How does tight ligand binding tightness
influence protein function?</div>""<div>•<span style=""font-weight: bold;"">Binding
constants</span>
range from <span style=""font-weight: bold;"">10⁻³
to 10⁻¹² M</span>—<span style=""font-weight: bold;"">tighter
binding</span>
means <span style=""font-weight: bold;"">greater
energy change</span>.</div>
<div>•This
energy can drive <span style=""font-weight: bold;"">conformational changes</span>, not
just heat release.</div>
<div>•In <span style=""font-weight: bold;"">ATP-related
enzymes</span>,
tight ATP binding:</div>
<div>•<span style=""font-weight: bold;"">Triggers conformational opening</span>
(e.g., before ATP hydrolysis).</div>
<div>•<span style=""font-weight: bold;"">Prepares enzyme for catalysis</span> by
shifting to a hydrolysis-competent state.</div>
<div>•<span style=""font-weight: bold;"">Hydrolysis</span> then drives the <span style=""font-weight: bold;"">power
stroke</span>
(large structural release).</div>
<div>•<span style=""font-weight: bold;"">Denaturants</span> like
<span style=""font-weight: bold;"">urea
or SDS</span>
increase flexibility and <span style=""font-weight: bold;"">weaken strong binding</span> even
before full denaturation.</div>"
"<div>Why are some protein binding sites hard
to identify, and how are they visualized?</div>""<div><span style=""font-weight: bold;"">Binding sites</span> can
be <span style=""font-weight: bold;"">spread
out</span>
across the protein surface and are often <span style=""font-weight: bold;"">difficult to identify</span>
without knowing the <span style=""font-weight: bold;"">3D structure</span>.</div>
<div>Frequently located on <span style=""font-weight: bold;"">loops
or surface protrusions</span>,
such as the <span style=""font-weight: bold;"">helix-turn-helix (HTH)</span>
motif used in <span style=""font-weight: bold;"">DNA binding</span>.</div>
<div><span style=""font-weight: bold;"">Examples</span>:</div>
<div><ul><li>&nbsp;<span style=""font-weight: bold;"">Human
growth hormone (yellow)</span>
binds <span style=""font-weight: bold;"">two
receptor molecules</span>
(green &amp; red), seen clearly in a <span style=""font-weight: bold;"">space-filling model</span>.</li><li>&nbsp;<span style=""font-weight: bold;"">Diphtheria
toxin gene repressor</span>
binds <span style=""font-weight: bold;"">tox
operator DNA</span>
via <span style=""font-weight: bold;"">loops
in the major groove</span>
(HTH).</li><li>&nbsp;<span style=""font-weight: bold;"">Gal4
transcription factor</span>
binds DNA with a <span style=""font-weight: bold;"">zinc finger domain</span>,
stabilized by a <span style=""font-weight: bold;"">loop</span>, also targeting the <span style=""font-weight: bold;"">major
groove</span>.</li></ul><div><img src=""paste-f08abf652499caa8e3fd335d526c05f94e37921b.jpg""><br></div></div><div><img src=""paste-848f664475f74a6d44349605a856668ff4cc2ba3.jpg""><br></div><div><br></div>
<div></div>"
<div>Why called cytochrome p450?&nbsp;</div>"<div>two different types of hemes. All of them
transfer electrons, but only a few accept oxygen as an electron acceptor. Those
that do bind to oxygen are called p450 because when they bind the absorbance
changes from 420 to 450.&nbsp;</div>"
"<div>How do deep binding pockets aid enzymatic
catalysis, and what example illustrates this?</div>""<div><span style=""font-weight: bold;"">Deep binding pockets</span>
surround substrates to <span style=""font-weight: bold;"">block water access</span> and
ensure <span style=""font-weight: bold;"">precise
shape complementarity</span>.</div>
<div>Example: <span style=""font-weight: bold;"">Bacterial cytochrome P45</span></div><div><ul><li><span style=""font-weight: bold;"">Oxidizes
camphor</span> by
inserting oxygen via a <span style=""font-weight: bold;"">heme group</span></li><li><span style=""font-weight: bold;"">Camphor
binds deep</span>
within the pocket, close to the heme.</li><li><span style=""font-weight: bold;"">No
clear exit path</span>
exists — <span style=""font-weight: bold;"">conformational
changes</span> are
needed to allow substrate entry and product release.</li></ul><div><img src=""paste-6368cf58e210c2930e78025d8e53611f6c3082a7.jpg""><br></div></div>
"
"<div>Where
are catalytic sites often located in multi-subunit or multi-domain proteins?</div>""<div>•<span style=""font-weight: bold;"">Catalytic
sites</span>
often form at the <span style=""font-weight: bold;"">interface between subunits or structural
domains</span>.</div>
<div>•In
proteins with <span style=""font-weight: bold;"">different subunits</span>, the
catalytic site is usually located <span style=""font-weight: bold;"">between two unlike surfaces</span>.</div>
<div>•<span style=""font-weight: bold;"">Multi-domain
proteins</span> can
have catalytic sites <span style=""font-weight: bold;"">spanning across domains</span>,
requiring both parts for full activity.</div>"
"<div>What role do exposed hydrophobic areas
play in binding and self-association?</div>""<div><span style=""font-weight: bold;"">Binding sites</span>
often contain <span style=""font-weight: bold;"">exposed hydrophobic regions</span> that
facilitate <span style=""font-weight: bold;"">ligand
interaction</span> and <span style=""font-weight: bold;"">membrane
anchoring</span>.</div>
<div>Example: <span style=""font-weight: bold;"">Cytochrome b6</span></div>
<div>•Shows
<span style=""font-weight: bold;"">heme
group (red)</span>
surrounded by <span style=""font-weight: bold;"">hydrophobic pocket (yellow)</span>.</div>
<div>•Enables
<span style=""font-weight: bold;"">self-association</span> and <span style=""font-weight: bold;"">electron
transfer</span>
between <span style=""font-weight: bold;"">donor
and acceptor pairs</span>.</div>
<div>•Anchored
in the membrane, allowing <span style=""font-weight: bold;"">swaying motion</span>
between partners.</div>
<div><span style=""font-weight: bold;"">Large hydrophobic domains</span> may
promote <span style=""font-weight: bold;"">self-association</span>,
while <span style=""font-weight: bold;"">small
ones</span>
usually do <span style=""font-weight: bold;"">not
cause aggregation</span>.</div>
<div><span style=""font-weight: bold;"">Self-association</span>
refers to the process where <span style=""font-weight: bold;"">identical or similar protein
molecules interact with each other</span> to form <span style=""font-weight: bold;"">dimers, oligomers, or larger
aggregates</span>, <span style=""font-weight: bold;"">without
the need for other types of molecules</span>.</div><div><br></div><div><img src=""paste-4750295ae37cc512471ee442daa85b022027b4cd.jpg""><br></div>"
"<div>How do exposed hydrophobic regions
contribute to signaling and reversible interactions?</div>""<div><span style=""font-weight: bold;"">Exposed hydrophobic domains</span>
promote <span style=""font-weight: bold;"">dimerization</span> and <span style=""font-weight: bold;"">protein-protein
interactions</span>.</div>
<div><span style=""font-weight: bold;"">Weak, reversible interactions</span>
enable <span style=""font-weight: bold;"">partner
swapping</span>,
essential in <span style=""font-weight: bold;"">signal transduction</span>.</div>
<div>Example: <span style=""font-weight: bold;"">JAK-STAT pathway</span></div>
<div><ul><li>JAK
kinases <span style=""font-weight: bold;"">phosphorylate
tyrosine residues</span>
on receptor tails.</li><li><span style=""font-weight: bold;"">STAT
proteins</span> bind
via <span style=""font-weight: bold;"">SH2
domains</span>, get
phosphorylated, and then <span style=""font-weight: bold;"">dimerize</span> via their own SH2 domains.</li><li><span style=""font-weight: bold;"">STAT
dimers</span> move
to the <span style=""font-weight: bold;"">nucleus</span> to <span style=""font-weight: bold;"">activate
gene expression</span>
and drive cellular responses.</li></ul></div>
"
"<div>What is domain swapping, and how does it
aid in protein assembly?</div>""<div><span style=""font-weight: bold;"">Domain swapping</span>
occurs when a domain that normally folds back to interact with its own protein <span style=""font-weight: bold;"">is
replaced by a similar domain from a neighboring subunit</span>.</div>
<div>Example: <span style=""font-weight: bold;"">Papilloma virus capsid protein</span></div>
<div><ul><li>The <span style=""font-weight: bold;"">C-terminal
arm (red)</span>
initially folds back to interact with its own protein.</li><li>During
<span style=""font-weight: bold;"">coat
assembly</span>,
this domain <span style=""font-weight: bold;"">swaps out</span> and binds to an adjacent subunit,
stabilizing the viral capsid.</li></ul></div>
"
"<div>How
does domain swapping regulate protein kinase activity?</div>""<div><ul><li>In <span style=""font-weight: bold;"">PAK1 protein kinase</span>, the
<span style=""font-weight: bold;"">regulatory
subunit binds and inhibits the active site</span>.</li><li>When <span style=""font-weight: bold;"">Cdc42-GTP</span>
binds to the regulatory domain, it causes a <span style=""font-weight: bold;"">conformational change</span>.</li><li>This <span style=""font-weight: bold;"">frees the catalytic domain</span> by <span style=""font-weight: bold;"">swapping
out the inhibitory interaction</span>, allowing kinase activity</li></ul></div>
"
"<div>How does affinity labeling help identify
specific ligand binding sites?</div>""<div><ul><li>In <span style=""font-weight: bold;"">affinity
labeling</span>, a <span style=""font-weight: bold;"">ligand
analog</span> is
designed with a <span style=""font-weight: bold;"">reactive chemical group</span>.</li><li>After
binding to its <span style=""font-weight: bold;"">target site</span>, the reactive group <span style=""font-weight: bold;"">forms
a covalent bond</span>,
permanently tagging the site.</li><li>This
method allows for <span style=""font-weight: bold;"">precise identification</span> of
active or binding sites using techniques like <span style=""font-weight: bold;"">mass spectrometry</span> or <span style=""font-weight: bold;"">radioactive
labeling</span></li></ul></div>
"
"<div>What
is photolabeling, and how does it work?</div>""<div><span style=""font-weight: bold;"">Photolabeling</span> uses
a ligand with a <span style=""font-weight: bold;"">photo-reactive group</span>,
like an <span style=""font-weight: bold;"">azide</span>.After binding, <span style=""font-weight: bold;"">UV
light</span>
activates the azide,
forming a <span style=""font-weight: bold;"">nitrene</span> — a <span style=""font-weight: bold;"">highly
reactive species</span>.The nitrene <span style=""font-weight: bold;"">covalently
inserts</span> into
nearby amino acid side chains at the <span style=""font-weight: bold;"">binding site</span>.The exact site of labeling can be found
using <span style=""font-weight: bold;"">mass
spectrometry</span>
or <span style=""font-weight: bold;"">radioactive
detection</span>.</div>"
"<div>What are the general features of ligand
binding and the role of bifunctional reagents?</div>""<div><ul><li>Typically,
<span style=""font-weight: bold;"">1–2
ligands</span> bind
per <span style=""font-weight: bold;"">protein
domain</span>;
different domains may bind different ligands.</li><li><span style=""font-weight: bold;"">Bifunctional
reagents</span> can
bind to <span style=""font-weight: bold;"">two
different parts of a protein</span> or <span style=""font-weight: bold;"">two protein partners</span>,
identifying <span style=""font-weight: bold;"">loose or dynamic interactions</span>
(e.g., in <span style=""font-weight: bold;"">swapping
enzyme complexes</span>).</li><li>These
are useful for mapping <span style=""font-weight: bold;"">transient or weak interactions</span>
between protein subunits or domains.</li></ul></div>
"
"How
can proteins bind ligands that are not complementary to their normal
conformation?""Proteins
can adopt rare variant conformations that are stabilized upon binding to
non-complementary (""odd"") ligands. If the variant binds tightly (KaV≫KaN ​), it becomes more populated despite a low
equilibrium constant for flexibility (Kflex≪1)"
"<div>If Kflex=10−3 and KaV=10^4, what
percent of the protein is in the variant conformation when the ligand is
present?</div>""<div>91% of the protein will be in the variant form due to the strong binding,
calculated from:</div><div><img src=""paste-cffa6df573acfb102ea467b52c7f6bb511f1a9ea.jpg""><br></div><div><img src=""paste-735a61d2bd5f6737ee0375074e8eb1f278a84910.jpg""><br></div><div><br></div>"
"<div><b>Q:</b><br>
What is the formula for the association constant Ka in protein-ligand binding?</div>""<img src=""paste-3b3ab925d0e27fd7f56e95402025f5c809316b82.jpg"" width=""1685"">"
"<div>How do you express the ratio of bound to free protein in terms of ligand
concentration?</div>""<img src=""paste-e4f3a542176c3fd18893cb6de10f498364cb999c.jpg"" width=""936"">"
"What
is the formula for the fraction y of total protein bound to ligand?""<div>This is useful for binding curves and
saturation plots.<img alt=""A black background with white text
Description automatically generated"" src=""clip_image001-b947d3d1f294251515af4f4efe6dc64366b43a16.png"" width=""1320""></div>"
"If
two ligands A and B bind to the same protein site, how do you determine which
one binds more?""<div>Compare their dissociation constants Kd​:</div>
<ul>
<li>Lower Kd = stronger binding</li>
<li>If both are at the same
concentration, the ligand with the <b>smaller Kd​</b> will dominate
binding</li></ul>"
<div>What is the formula comparing binding of ligands A and B to the same protein?</div>"<img src=""paste-db6ec22b260fdb8d951e621b894a94c75133332a.jpg""><br><div>This reflects the competition outcome
based on both affinity and concentration.</div>"
<div>What is the formula for the free energy of binding (ΔGb)</div>"<div><img src=""clip_image001-10478c0e77980912ce5ed375ef01633f93a137f9.png""></div>
<div>This quantifies how favorable the
binding is thermodynamically.
·&nbsp; When multiple ligands compete,
the one with a <b>lower Kd​</b> and/or <b>higher concentration</b> will bind
more.The equilibrium ratio and free energy equations help quantify and compare
these effects.</div>
<div>&nbsp;</div>
<div>&nbsp;</div>"
"<div>What is a Scatchard plot and what can
it tell us about ligand binding?</div>""<div>A Scatchard plot graphs the ratio of <b>bound
to free ligand</b> ([PL]/[L​) versus the <b>concentration of bound ligand</b> [PL].
It is used to determine the binding constant Ka​, and the X-intercept gives Bmax
the total binding capacity. A <b>linear plot</b> indicates non-cooperative
binding, while <b>curved plots</b> indicate <b>positive</b> or <b>negative
cooperativity</b>.</div><div><img src=""paste-c2933fc952970aada955291fcf7c0125e14d6366.jpg""><br></div>"
"<div>How can Scatchard plots help determine Dissociation
Constant Kd and maximum binding capacity Kd?</div>""
<table>
<tbody><tr>
<td></td>
</tr>
<tr>
<td></td>
<td>By subtracting nonspecific binding from total binding, you obtain a specific
binding isotherm. This hyperbolic curve can be replotted as a <strong>Scatchard plot</strong>
(bound/free vs. bound). The slope gives −1/KD ​, and the X-intercept gives Bmax
allowing determination of the dissociation constant and total binding &nbsp;capacity&nbsp; &nbsp; &nbsp;<div>
<table>
<tbody><tr>
<td></td>
</tr>
<tr>
<td></td>
<td><img alt=""A plot of both total and non specific binding followed by the specific binding."" src=""clip_image001-1a9d0b67a7dab2dfcc6bd09e07b9119145d25eaa.png"" width=""962""></td>
</tr>
</tbody></table><img src=""paste-584f3c591eb2042e6849ac5ed6a89ea47368a91a.jpg""><br><br>
<br></div></td></tr></tbody></table>"
"<img src=""paste-2351807e0f711df50b166ae7d448b2ff5b8d2153.jpg""><br><div>How is Graph D related to Graph B, and
what does it show?&nbsp;</div>""<div>Overall Show Monomeric Binding </div>
<div>&nbsp;Graph A shows a <strong>hyperbolic binding isotherm</strong>:
fraction bound [P⋅A]
vs. ligand concentration [A]. Graph Cis
the Scatchard transformation of Graph A giving a straight line for
non-cooperative 1:1 binding.&nbsp;</div>"
"<img src=""paste-2351807e0f711df50b166ae7d448b2ff5b8d2153.jpg""><br><div>How is Graph D related to Graph B, and
what does it show?</div>""<div>Overall Show Cooperative Binding </div>
<div>Graph
B shows a <strong>sigmoidal curve</strong>
of fractional binding vs. log([A]),
indicating <strong>cooperative
binding</strong> and dissociation constant is changing. Log-Log scatchard
like plot defines cooperativity .&nbsp;</div>"
"<div>How does Isothermal Titration
Calorimetry (ITC) measure small molecule binding to a protein?</div>""<div>ITC
measures the <strong>heat
released or absorbed</strong> during ligand binding by titrating the
ligand-small molceures into a protein sample and recording the <strong>power needed to keep the
sample and reference cells at equal temperature</strong>. he resulting
data curve (heat per injection vs. molar ratio) is integrated to determine:<br><img src=""paste-e9866d1e59270f598f4487d33747ee14c11447f9.jpg"" width=""1078""><br></div>"
"<div>What is Surface Plasmon Resonance (SPR) used to detect
in biochemistry?</div>""<div><b>A:</b> SPR detects <b>real-time binding interactions</b>
between biomolecules by monitoring changes in light reflection from a gold
surface, indicating changes in surface mass due to binding.</div>"
"What
physical phenomenon causes the SPR- Surface Plasmon Resonance&nbsp; signal?""<div><b>A:</b> SPR occurs when <b>light reflects off a gold surface</b>
and interacts with <b>free electrons (plasmons)</b>, producing a dip in
reflected light at a specific angle, which shifts when binding occurs.</div><div><img src=""paste-69d778eddd94fa9ea6e3ab891e3964718ee8e557.jpg"" width=""1011""><br></div><div><br></div>"
"<div>Why is the angle of light reflection
important in SPR measurements?</div>""The <b>angle of light</b> hitting the gold film
is critical.<b>Only
at a specific angle</b>
(θ₀),
plasmons
are excited.A shift in this angle indicates <b>a change in surface mass</b>,
i.e., binding has occurred.<br><img src=""paste-e2cf321ef060bfb790f0b3935c84e5379c48e719.jpg"">"
"<div>&nbsp;What is the purpose of a flow
cell in Surface Plasmon Resonance (SPR)/Plasmon Resonance &nbsp;experiments?&nbsp;</div>""<div>A flow cell delivers samples over the
sensor surface, allowing <b>continuous monitoring</b> of association,
dissociation, and regeneration phases of binding in real time.</div><div><img src=""paste-47c299d303384cbdc910bb93d3af5c90edc6fa22.jpg""><br></div><div><img src=""paste-1155351dab15730d388c11eefc55443cee674673.jpg""><br></div><div><br></div>"
<div><b>Q:</b> What information can be extracted from SPR data?</div>"<div>·&nbsp; <b>Binding kinetics</b>
(association/dissociation rates)</div>
<div>·&nbsp; <b>Affinity (Kₐ/K_d)</b></div>
<div>·&nbsp; <b>Concentration dependence</b></div>
<div>·&nbsp; <b>Inhibitory effects</b> (e.g.,
drug blocking)</div>
<div><img alt=""types of data obtained using plasmon resonance. titration curves can be done as well as binding constants"" src=""clip_image001.jpg"" width=""835""></div>
<div>&nbsp;\</div>"
How is the cell cycle controlled?&nbsp;"<div>The
cell cycle is controlled by Cyclin-dependent kinase (cdk) via
proten-protein
interactions with a cyclin for activation. After cyclin binding, Cdks
undergo <span style=""font-weight: bold;"">phosphorylation or
dephosphorylation</span>,
depending on the type of Cdk and the regulatory signals present.</div><div><br></div><div><img src=""paste-b558bf1fb7acd0dc7a5f379b450057b3bb0f65da.jpg""><br></div>"
"<div>What
regulates cyclin binding to Cdk?</div>""<div>Cyclin
binding is tightly regulated by the <span style=""font-weight: bold;"">concentration
of cyclin</span>, which fluctuates in a controlled manner
during the cell cycle.</div>
<div>Which enzymes control Cdk
phosphorylation?</div>
<div><span style=""font-weight: bold;"">CAK (</span>Cdk-activating kinase) or other Cdk-activating
enzymes phosphorylate Cdk <span style=""font-weight: bold;"">only
when cyclin is bound</span>,
while other <span style=""font-weight: bold;"">kinases and phosphatases</span> regulate additional inhibitory or
activating si</div>"
"<div>Q How do small protein domains contribute
to cell signaling and control?</div>""<div>Small protein domains are <span style=""font-weight: bold;"">modular</span> and have <span style=""font-weight: bold;"">distinct binding properties</span> that allow them to control and regulate
information flow in cells by interacting with DNA, proteins, or small molecules
based on chemical context.</div>"
<div>Why are interaction domains considered versatile in proteins?</div>"<div>Interaction domains are <span style=""font-weight: bold;"">independently folded</span> and can function while attached to
larger proteins. Their <span style=""font-weight: bold;"">order
and combination</span> in a
protein can vary, enabling <span style=""font-weight: bold;"">specific
and versatile binding behaviors</span>
without disrupting core enzymatic functions.</div>
<div>For
example, Cy
phospholipase has two SH2 and one SH3 domains inserted in the catalytic domain
without disturbing enzymatic activity or having their sites blocked.&nbsp;&nbsp;</div>"
"<div>How does cellular location help regulate
protein function and prevent mis-modification?</div>""<div>Proteins like kinases are localized near
their substrates to ensure correct modifications and avoid acting on the wrong
targets. Spatial and temporal organization—such as where and when proteins like
Tem1 are expressed—helps regulate specificity, even when one protein can act on
many targets.</div>
Eg.
GTPase Tem1 found in<span style=""font-style: italic;"">
S. cerevisiae</span> is involved in termination of the
mitotic phase.&nbsp; It can modify 24
different proteins but can react with only 4 at a time.&nbsp; Targeting Tem1 to different locations with
different substrates helps solve the timing problem<br>"
"<div>What are the three main ways to target a
protein in the cell?</div>""<div>1.<span style=""font-weight: bold;"">Targeting
sequences</span> (e.g., signal peptides or transit
peptides,&nbsp; KDEL/ER, KRKR/nucleus)</div>
<div>2.<span style=""font-weight: bold;"">Post-translational
modifications</span> (e.g., phosphorylation enabling SH2
binding and subsequent receptor dimerization)</div>
<div>3.<span style=""font-weight: bold;"">Scaffold
binding</span> to bring proteins into specific
signaling complexes or locations -</div><div><br></div><div>&nbsp;<img src=""paste-8679176336ca20aa5ada5aa9171b07ff3192a071.jpg"" width=""647""></div>"
"<div>How
do membrane anchoring and scaffolds help with protein targeting?</div>""<div>Membrane anchoring (e.g., G-proteins)
ensures proteins are in the correct place to act without mis-targeting. <span style=""font-weight: bold;"">Scaffold proteins</span> organize and localize signaling
components to promote efficiency and specificity in cellular responses.
Overall, help bind proteins where they are needed.&nbsp;</div>"
"<div>How
do pH changes regulate protein function?</div>""<div>pH
affects the <span style=""font-weight: bold;"">surface charge and solubility</span> of proteins by protonating acidic
residues (Asp/Glu), which can alter structure and enable functions like
membrane insertion or activation of enzymes like Cathepsin D under acidic
conditions. Cathepsin D, an acidic endopeptidase, becomes active under acidic
conditions by rearrangement of the N-terminus out and away from the active
site.&nbsp;</div><div><img src=""paste-2d2b6f1f4d5cdf0e1a5210dab3b1d56c188edd4a.jpg""><br></div><div><br></div><div><br></div>"
"<div></div>
<div>How
does the redox environment regulate protein structure?</div>""<div>In
the <span style=""font-weight: bold;"">reducing environment of the cell</span>, SH groups remain free, preventing
disulfide bond formation. But upon secretion, proteins like <span style=""font-weight: bold;"">acetylcholine esterase</span> form <span style=""font-weight: bold;"">disulfide
bonds (S–S)</span> that stabilize <span style=""font-weight: bold;"">active multimeric structures</span> such as tetramers. Acetylcholine
esterase is produced as a monomer but when secreted into the synapse the inter
subunit S—S bonds on the C-terminal end form an active&nbsp; tetramer.</div>"
"<div>What
is diphtheria toxin and what does it do?</div>""<div>Diphtheria
toxin is a <span style=""font-weight: bold;"">bacterial exotoxin</span> produced by <span style=""font-style: italic;"">Corynebacterium diphtheriae</span>. It is an <span style=""font-weight: bold;"">AB toxin</span>
where the <span style=""font-weight: bold;"">A domain</span> is toxic and the <span style=""font-weight: bold;"">B domain</span>
binds to host cells. It causes <span style=""font-weight: bold;"">cell
death</span> by blocking protein synthesis and is
responsible for the symptoms of <span style=""font-weight: bold;"">diphtheria</span>.</div>"
"<div><span style=""font-weight: bold;"">&nbsp;Mechanism of Action of </span><span style=""font-weight: bold;"">Diphteria</span><span style=""font-weight: bold;""> Toxin:&nbsp;</span></div>""<div>1.<span style=""font-weight: bold;"">Binding:</span><br>
The <span style=""font-weight: bold;"">B domain</span> binds to the <span style=""font-weight: bold;"">HB-EGF-like receptor</span> on human cells.</div>
<div>2.<span style=""font-weight: bold;"">Endocytosis:</span><br>
The toxin is internalized via <span style=""font-weight: bold;"">receptor-mediated
endocytosis</span>.</div>
<div>3.<span style=""font-weight: bold;"">Low
pH Activation:</span><br>
Acidification of the endosome <span style=""font-weight: bold;"">triggers
a conformational change</span>,
allowing the <span style=""font-weight: bold;"">T domain</span> (a part of B) to insert into the
membrane and form a pore.</div>
<div>4.<span style=""font-weight: bold;"">Translocation:</span><br>
The <span style=""font-weight: bold;"">A domain</span> crosses into the cytosol through this
pore.</div>
<div>5.<span style=""font-weight: bold;"">Toxic
Action:</span><br>
The A domain catalyzes <span style=""font-weight: bold;"">ADP-ribosylation
of EF-2 (elongation factor 2)</span>, an
essential protein in translation. This halts protein synthesis and <span style=""font-weight: bold;"">kills the cell</span>.</div><div><img src=""paste-a6bc17f7e4bca11050fa7a90f27727307587edbe.jpg""><br></div>"
<div>What are effector ligands and how do they influence enzyme activity?</div>"<div>Effector ligands are small molecules that
can bind to an enzyme’s <span style=""font-weight: bold;"">active
site</span> and <span style=""font-weight: bold;"">compete
with the substrate</span>, a
process called <span style=""font-weight: bold;"">competitive
inhibition</span>. This blocks the normal reaction from
occurring and is one way to regulate metabolic pathways, often seen in <span style=""font-weight: bold;"">feedback inhibition</span> where the product of a pathway shuts
down its own synthesis.</div>"
"<div>What does cooperative ligand binding
mean, and where does it occur?</div>""<div>Cooperative binding occurs in <span style=""font-weight: bold;"">multi-subunit proteins</span>, where binding of a ligand to one
subunit causes <span style=""font-weight: bold;"">conformational
changes</span> that affect ligand binding on another
subunit.</div>"
"
<p style=""margin-top: 4.32pt; margin-bottom: 0pt; direction: ltr; unicode-bidi: embed; vertical-align: baseline;""><span style=""color: rgb(255, 255, 255);"">How do positive and negative
cooperativity differ?</span></p>""<div>•<span style=""font-weight: bold;"">Positive
cooperativity</span>: the second ligand binds <span style=""font-weight: bold;"">faster and tighter</span>, shifting the binding curve to show a <span style=""font-weight: bold;"">steep increase</span> in binding over a narrow concentration
range.</div>
<div>•<span style=""font-weight: bold;"">Negative
cooperativity</span>: the second ligand binds <span style=""font-weight: bold;"">more slowly and loosely</span>, requiring <span style=""font-weight: bold;"">higher concentrations</span>.</div>"
"<div>What
is an allosteric site and how does it relate to protein regulation?</div>""<div>An <span style=""font-weight: bold;"">allosteric site</span> is a binding site <span style=""font-weight: bold;"">away from the active site</span> that, when bound by a ligand, causes a <span style=""font-weight: bold;"">conformational change</span> in the protein. This change can affect
activity by propagating structural shifts through tightly packed amino acids.</div>"
"<div>What
are the two main models of allosteric regulation?</div>""<div><span style=""font-weight: bold;"">Sequential model</span>: ligands bind <span style=""font-weight: bold;"">one at a time</span>, converting individual subunits (e.g.,
from T → R with intermediates like RT).</div>
<div><span style=""font-weight: bold;"">Concerted model</span>: all subunits shift <span style=""font-weight: bold;"">together</span> from T (tense) to R (relaxed) upon
ligand binding, with no intermediates.</div><div><br></div><div><img src=""paste-ead61325056c8b4139f83c7f6893a0d9564e275b.jpg""><br></div>"
"<div>How is Aspartate transcarbamoylase (ATCase) regulated during pyrimidine
biosynthesis?</div>""<div>ATCase is
the first step in pyrimidine biosynthesis and has <span style=""font-weight: bold;"">separate regulatory and catalytic
subunits</span>. It is inhibited by <span style=""font-weight: bold;"">CTP</span>
(product) and activated by <span style=""font-weight: bold;"">ATP</span> (purine signal), helping balance
purine/pyrimidine levels.</div>
<div>•<span style=""font-weight: bold;"">T
state</span> = compact, less active</div>
<div>•<span style=""font-weight: bold;"">R
state</span> = open, more active (induced by ATP)</div>
<div>•<span style=""font-weight: bold;"">AI</span> = allosteric site, <span style=""font-weight: bold;"">Zn</span>
= zinc binding, <span style=""font-weight: bold;"">asp</span> = aspartate binding, <span style=""font-weight: bold;"">cp</span>
= carbamoyl phosphate site<br>
<span style=""font-weight: bold;"">Red and yellow regions</span> represent subunit interfaces altered by
ATP binding.</div><div><img src=""paste-c70dfa0ea3f5e758fa20a7d26024fcd1fa6533b4.jpg"" width=""656""><br></div>"
"<div>What
role do ATP and GTP play in motor proteins and molecular switches?</div>""<div>ATP
or GTP binds with <span style=""font-weight: bold;"">high
affinity (</span><span style=""font-weight: bold;"">nM</span><span style=""font-weight: bold;""> </span><span style=""font-weight: bold;"">Kd</span><span style=""font-weight: bold;"">)</span>
and induces a <span style=""font-weight: bold;"">strained
active conformation</span> in
the protein. Hydrolysis to ADP or GDP causes a <span style=""font-weight: bold;"">snap back</span>
to a relaxed state, releasing energy used for <span style=""font-weight: bold;"">motion (motors)</span> or <span style=""font-weight: bold;"">signaling
(switches. </span>Motor proteins use <span style=""font-weight: bold;"">ATP binding and hydrolysis</span> to convert chemical energy into <span style=""font-weight: bold;"">kinetic energy</span>, enabling them to ""walk"" or
move cargo along cytoskeletal tracks like actin filaments or microtubules.</div>"
"<div>How do G-protein coupled switches use
GTP?</div>""<div>GTP
binding ""cocks"" the switch, and GTP hydrolysis <span style=""font-weight: bold;"">triggers conformational changes</span> that relay environmental signals (e.g.,
sight, smell, homeostasis). G-proteins are the <span style=""font-weight: bold;"">largest protein signaling family</span> in eukaryotes.</div>"
"<div>What structural features allow motor and
switch proteins to bind ATP or GTP?</div>""<div>Motor and switch proteins share a
conserved structure built around:</div>
<div>•<span style=""font-weight: bold;"">Two
switch domains (Switch I and Switch II)</span> –
These flexible regions undergo major shape changes when the nucleotide is bound
and again after it's hydrolyzed.</div>
<div>•A <span style=""font-weight: bold;"">P-loop (phosphate-binding loop)</span> – This motif clamps tightly onto the <span style=""font-weight: bold;"">γ-</span><span style=""font-weight: bold;"">phosphate</span>
of ATP or GTP in the ""loaded"" state.</div>
<div>These domains form a <span style=""font-weight: bold;"">nucleotide-binding pocket</span>, allowing the protein to
""sense"" whether it is bound to a triphosphate (ATP/GTP) or
diphosphate (ADP/GDP), which governs activation or inactivation.</div>"
"<div>How
does ATP or GTP binding lead to protein activation or signaling?</div>""<div>Binding of <span style=""font-weight: bold;"">ATP or GTP</span>
(PuTP- <span style=""font-weight: bold;"">purine
triphosphate</span>) triggers a <span style=""font-weight: bold;"">tight, high-energy conformation</span> in the protein. This often moves a <span style=""font-weight: bold;"">key catalytic residue</span>—typically <span style=""font-weight: bold;"">Serine (Ser) or Threonine (</span><span style=""font-weight: bold;"">Thr</span><span style=""font-weight: bold;"">)</span>—into
an active position.</div>
<div>•Hydrolysis
of the γ-phosphate (red arrow in the figure) is <span style=""font-weight: bold;"">acid-catalyzed</span> and flips the protein into a <span style=""font-weight: bold;"">relaxed conformation</span>.</div>
<div>•This
switch converts <span style=""font-weight: bold;"">chemical
energy</span> into <span style=""font-weight: bold;"">kinetic
motion</span> (motor proteins) or <span style=""font-weight: bold;"">molecular signaling</span> (e.g., GTPases).</div><div><br></div><div><img src=""paste-b386834cfdb1deb2ba90a5e20a24586f3b84a6f8.jpg"" width=""631""><br></div>"
"<div>What
is Ras and how does it regulate intracellular signaling?</div>""<div>Ras is a <span style=""font-weight: bold;"">small GTPase (G-protein)</span> that acts as a molecular switch in
signal transduction.</div>
<div>In the <span style=""font-weight: bold;"">inactive ""off"" state</span>, Ras is bound to <span style=""font-weight: bold;"">GDP</span>.</div>
<div>Upon receiving a signal, Ras exchanges
GDP for <span style=""font-weight: bold;"">GTP</span>,
becoming <span style=""font-weight: bold;"">active</span>.</div>
<div>Active Ras (Ras•GTP)
initiates <span style=""font-weight: bold;"">downstream signaling pathways</span> that promote <span style=""font-weight: bold;"">cell growth and differentiation</span>.</div>
<div>Ras has intrinsic GTPase activity which,
with the help of <span style=""font-weight: bold;"">GAPs</span>, hydrolyzes GTP to GDP, returning it to
the <span style=""font-weight: bold;"">inactive state</span>.</div>
<div>This cycle allows <span style=""font-weight: bold;"">tight control</span> over signaling duration and intensity.</div><div><img src=""paste-ec56e2b6d0259490dbd20e0220e9b6dcb05135a8.jpg""><br></div><div><br></div>"
"<div>Describe
the sequence of events in the Ras activation and inactivation cycle.</div>""<div><span style=""font-weight: bold;"">1. Signal Detection:</span> Ras-GDP binds to a <span style=""font-weight: bold;"">Guanine nucleotide exchange factor
(GEF)</span> in response to upstream growth signals.</div>
<div><span style=""font-weight: bold;"">2. Activation:</span> GEF catalyzes the exchange of <span style=""font-weight: bold;"">GDP for GTP</span>, switching Ras to the <span style=""font-weight: bold;"">active (tense) state</span>.</div>
<div><span style=""font-weight: bold;"">3. Signal Transduction:</span> Active Ras interacts with <span style=""font-weight: bold;"">downstream effectors</span> to relay the signal inside the cell.</div>
<div><span style=""font-weight: bold;"">4. Inactivation:</span> <span style=""font-weight: bold;"">GTPase-activating
proteins (GAPs)</span> bind
to Ras-GTP and accelerate <span style=""font-weight: bold;"">GTP
hydrolysis</span> by 100,000-fold.</div>
<div><span style=""font-weight: bold;"">Resetting:</span> Ras•GDP returns to the <span style=""font-weight: bold;"">inactive state</span> and can be reactivated by another GEF
interaction.</div>"
<div>Where are Ras proteins located?</div>"<div>All Ras proteins undergo <span style=""font-weight: bold;"">covalent modification</span> by <span style=""font-weight: bold;"">lipophilic
groups</span> (e.g., farnesylation), which <span style=""font-weight: bold;"">anchor them to the plasma membrane</span> — a key feature for their function in
signaling.</div>"
"<div>What
is the structure heterotrimeric GTPases and how do they function in signal
transduction?</div>""<div><ul><li>Heterotrimeric GTPases are composed of <span style=""font-weight: bold;"">three subunits: </span><span style=""font-weight: bold;"">α, β, </span><span style=""font-weight: bold;"">and </span><span style=""font-weight: bold;"">γ</span>.</li><li>The <span style=""font-weight: bold;"">α-</span><span style=""font-weight: bold;"">subunit</span> binds GTP/GDP and has a similar fold to
the Ras protein, but with an <span style=""font-weight: bold;"">extra
helix</span> that projects into the active site.</li><li><span style=""font-weight: bold;"">β </span><span style=""font-weight: bold;"">and </span><span style=""font-weight: bold;"">γ
</span><span style=""font-weight: bold;"">subunits</span> form a stable complex via <span style=""font-weight: bold;"">coiled-coil interactions</span> and help anchor and regulate the α-subunit.</li><li>These GTPases are associated with <span style=""font-weight: bold;"">G-protein coupled receptors (GPCRs)</span>, which span the membrane via <span style=""font-weight: bold;"">7 helices</span>.</li><li>Upon ligand binding, the <span style=""font-weight: bold;"">GPCR acts like a GAP</span>, activating the α-subunit to exchange GDP for GTP.</li><li>This initiates intracellular signaling
cascades, relaying signals from the extracellular environment to the cell's
interior.</li><li><img alt=""GPCR | Learn Science at Scitable"" src=""U4CP2-2_ActivatedGPCR_ksm.jpg""><br></li></ul></div>
"
"<div>What
is EF-Tu and its mechanism?</div>""<div><ul><li><span style=""font-weight: bold;"">EF-Tu (Elongation Factor Tu)</span> is a <span style=""font-weight: bold;"">GTP-binding
protein</span> involved in <span style=""font-weight: bold;"">prokaryotic translation</span>.</li><li>It forms a complex with <span style=""font-weight: bold;"">GTP and aminoacyl-tRNA</span> and delivers the aminoacyl-tRNA to the <span style=""font-weight: bold;"">A site of the ribosome</span>. EF-Tu ensures that the <span style=""font-weight: bold;"">codon-anticodon pairing</span> is correct before hydrolyzing GTP.</li><li>Upon
correct pairing, <span style=""font-weight: bold;"">GTP
is hydrolyzed</span>, triggering the <span style=""font-weight: bold;"">release of tRNA</span> into the ribosome. EF-Tu, now bound to
GDP, becomes inactive and must be <span style=""font-weight: bold;"">reactivated
by EF-Ts</span> (its GEF) for another round.</li></ul><div><img src=""paste-a31feaa7643da88972b1500d7740ebbe881e1d85.jpg""><br></div></div>
"
"<div>What are Myosin and its mechanism of
action?&nbsp;</div>""<div><ul><li><span style=""font-weight: bold;"">Myosin</span> is a motor protein which walks along <span style=""font-weight: bold;"">actin filaments</span> using a rowing motion driven by ATP
hydrolysis. </li><li><span style=""font-weight: bold;"">Step 1:</span> ADP + Pi are in the active site (trap
set) while tightly bound to actin.</li><li><span style=""font-weight: bold;"">Step 2:</span> <span style=""font-weight: bold;"">Release
of Pi</span> (after hydrolysis) triggers a <span style=""font-weight: bold;"">power stroke</span>, bending the myosin head and moving the
filament.</li><li><span style=""font-weight: bold;"">Step 3:</span> <span style=""font-weight: bold;"">ATP
binding</span> causes myosin to <span style=""font-weight: bold;"">detach</span> from actin and <span style=""font-weight: bold;"">re-cock</span> for the next stroke.</li><li>The two heads of myosin operate in <span style=""font-weight: bold;"">opposite phases</span>, enabling continuous movement.</li></ul></div>
"
"<div>What
are kinesin and their mechanism of action?&nbsp;</div>""<div><ul><li><span style=""font-weight: bold;"">Kinesin</span> transports cargo along <span style=""font-weight: bold;"">microtubules</span> in a stepwise fashion powered by ATP.</li><li><span style=""font-weight: bold;"">Step </span><span style=""font-weight: bold;"">1:</span> ATP
binds to the <span style=""font-weight: bold;"">loosely attached foot</span>, causing it to bind tightly to the
microtubule.</li><li><span style=""font-weight: bold;"">Step 2:</span> This triggers <span style=""font-weight: bold;"">release of the rear foot</span>, which swings forward.</li><li><span style=""font-weight: bold;"">Step 3:</span> ADP is released from the front foot, and
ATP is hydrolyzed in the rear foot.</li><li><span style=""font-weight: bold;"">Step 4:</span> The cycle repeats, resulting in
processive “walking” along the microtubule.</li></ul></div>
"
"<div>How
do motor proteins use ATP binding and hydrolysis to drive mechanical movement?</div>""<div><ul><li><span style=""font-weight: bold;"">Motor proteins</span> (e.g., kinesin, myosin, G-proteins)
convert <span style=""font-weight: bold;"">tight ATP binding</span> into a <span style=""font-weight: bold;"">mechanical lever motion</span>.</li><li>The <span style=""font-weight: bold;"">“trap
state”</span> occurs when ATP is tightly bound,
locking the protein into a high-energy conformation.</li><li><span style=""font-weight: bold;"">Hydrolysis of ATP</span> releases the bound phosphate and
transitions the protein into a <span style=""font-weight: bold;"">relaxed
state</span>, moving structural domains called <span style=""font-weight: bold;"">switch I and switch II</span>.</li><li>This conformational shift <span style=""font-weight: bold;"">amplifies mechanical motion</span>, enabling:</li><li><span style=""font-weight: bold;"">(a)</span> Kinesin to step along microtubules</li><li><span style=""font-weight: bold;"">(b)</span> Myosin to pull on actin filaments</li><li><span style=""font-weight: bold;"">(c)</span> G-proteins to toggle between
active/inactive signaling states</li></ul></div><div><img src=""paste-77dc60cea4a17273ab16bd833e2641811cc29250.jpg""><br></div>
"
"<div>How is protein degradation regulated in
eukaryotic cells?</div>""<div>•Eukaryotic
cells regulate protein levels by controlling their <span style=""font-weight: bold;"">lifetime</span> using the <span style=""font-weight: bold;"">proteasome</span>.</div>
<div>•<span style=""font-weight: bold;"">Regulatory
proteins</span> (e.g., transcription factors) have <span style=""font-weight: bold;"">shorter lifespans</span> than structural proteins.</div>
<div>•<span style=""font-weight: bold;"">Damaged
or unneeded proteins</span> are
tagged with <span style=""font-weight: bold;"">ubiquitin</span>, a small protein that signals for
degradation.</div>
<div>•Ubiquitin
is covalently attached to <span style=""font-weight: bold;"">lysine
residues</span> by a <span style=""font-weight: bold;"">ubiquitinating
complex</span>.</div>
The <span style=""font-weight: bold;"">proteasome</span> recognizes polyubiquitinated proteins
and digests them into <span style=""font-weight: bold;"">peptides</span> and <span style=""font-weight: bold;"">recyclable
ubiquitin</span><br>"
"<div>Describe the role of ubiquitination in
regulating NFκB signaling.</div>""<div>•<span style=""font-weight: bold;"">NF</span><span style=""font-weight: bold;"">κ</span><span style=""font-weight: bold;"">B</span> is a
transcription factor <span style=""font-weight: bold;"">inhibited
by I</span><span style=""font-weight: bold;"">κ</span><span style=""font-weight: bold;"">B</span>,
which retains it in the cytoplasm.</div>
<div>•<span style=""font-weight: bold;"">Signal
cascades</span> lead to phosphorylation of IκB on <span style=""font-weight: bold;"">two
serine residues</span>,
triggering its <span style=""font-weight: bold;"">ubiquitination</span>.</div>
<div>•Ubiquitinated
IκB is <span style=""font-weight: bold;"">degraded
by the proteasome</span>,
releasing NFκB.</div>
<div>•<span style=""font-weight: bold;"">NF</span><span style=""font-weight: bold;"">κ</span><span style=""font-weight: bold;"">B then </span><span style=""font-weight: bold;"">translocates</span><span style=""font-weight: bold;""> to the nucleus</span> and activates target genes.</div>
<div>•In
another example, <span style=""font-weight: bold;"">HIF-1</span><span style=""font-weight: bold;"">α</span>
is targeted for degradation by an <span style=""font-weight: bold;"">oxygen-sensing prolyl hydroxylase</span>.</div>
<div>•Under
<span style=""font-weight: bold;"">normoxic</span><span style=""font-weight: bold;""> conditions (O₂ &gt; 5%)</span>, HIF-1α
is hydroxylated and ubiquitinated.</div>
<div>•Under
<span style=""font-weight: bold;"">hypoxia (O₂ &lt; 5%)</span>, hydroxylase activity is suppressed, <span style=""font-weight: bold;"">stabilizing HIF-1</span><span style=""font-weight: bold;"">α</span>.</div>"
Given that Orotidine 5′-monophosphate decarboxylase is one of the most highly rate-enhancing enzymes, accelerating UMP production by 10¹⁷-fold, does this mean it alters the equilibrium constant of the reaction?"<div>No, Orotidine 5′-monophosphate decarboxylase (ODCase) does <strong>not alter the equilibrium constant</strong> of the reaction.</div>
<div>Enzymes like ODCase <strong>only speed up the rate</strong> at which equilibrium is reached by lowering the <strong>activation energy</strong> of the reaction. The <strong>equilibrium constant (Keq)</strong> is determined solely by the <strong>free energy difference (ΔG°')</strong> between the reactants and products, and this is unaffected by the presence of an enzyme.</div><div>- This is just a result of smple combinations of a few basic priciples that cause the dramatic increase in rate.&nbsp;</div>"
"<div>What general strategies do enzymes use to accelerate chemical reactions?</div>
<div></div>""<ul><li><div><strong>Orienting substrates correctly</strong> for the reaction</div>
</li><li>
<div><strong>Stabilizing transition states and reactive intermediates</strong></div>
</li><li>
<div><strong>Polarizing bonds</strong> to make them more reactive</div>
</li></ul>
<strong><ul><li><strong>Forming transient covalent intermediates</strong></li></ul></strong>
<ul><li>
<div><strong>Using acid/base residues</strong> to increase local concentration and reactivity</div></li></ul><div>These strategies work together to <strong>lower the activation energy (ΔG‡)</strong> and speed up the approach to equilibrium.<br></div>"
"<div>Why is the transition state important in enzymatic reactions?</div>
<div></div>""<ul><li><div>The <strong>transition state</strong> is the highest-energy point between reactants and products.</div>
</li><li>
<div>Enzymes work by <strong>stabilizing this state</strong>, lowering the energy needed to reach it (ΔG‡).</div>
</li><li>
<div>The time spent in the transition state is extremely brief (∼10⁻¹⁵ seconds), the time of a single bond vibration.</div>
</li><li>
<div>The difference in ΔG‡ between catalyzed and uncatalyzed reactions (<strong>ΔG‡_cat vs. ΔG‡_uncat</strong>) explains rate acceleration.</div></li></ul><div>Enzymes <strong>don’t change the overall free energy (ΔG)</strong>—they just make it faster to reach the end.<br></div>
"
"<div>What role do electrostatic potential lines play in enzyme-substrate interactions? This ezyme is superoxide dismutase and repsonsible for binding the ngativr charged superoxide O2- ion.&nbsp;</div><div><img src=""paste-6fc980449f9efd47ccf60c5536536735a5b417f6.jpg""><br></div>
<div></div>""<ul><li><div>Electrostatic potential lines <strong>guide substrates</strong> into the enzyme's active site.</div>
<ul>
<li>
<div><strong>Blue lines = positive charges</strong></div>
</li>
<li>
<div><strong>Red lines = negative charges</strong></div></li></ul></li><li>
<div>The enzyme uses <strong>positively charged regions</strong> to <strong>attract and direct</strong> superoxide into the active site.</div>
</li><li>
<div>This reduces <strong>unproductive binding</strong> and <strong>increases catalytic efficiency</strong>.</div></li></ul>
"
"<div>How do electrostatics support induced fit and substrate retention?</div><div><img src=""paste-35b6255a8137a2c77f8e232660c66e164b89db7f.jpg""><br></div>
<div></div>""<ul><li><div>Electrostatics <strong>hold the binding pocket closed</strong> until the substrate begins to bind.</div>
</li><li>
<div>Upon substrate approach, the enzyme undergoes an <strong>induced fit</strong>, opening up to accommodate the substrate.</div>
</li><li>
<div><strong>Complementary charges</strong> between the enzyme and substrate <strong>stabilize the interaction</strong>, keeping the substrate locked in.</div>
</li><li>
<div>This ensures <strong>precise positioning for catalysis</strong> and avoids premature release.</div></li></ul>&nbsp;Electrostatic guidance not only attracts the substrate but also stabilizes the <strong>transition state</strong> for optimal reaction.<br>
"
"<div>Why is protein folding essential for efficient catalysis in enzymes?</div>
<div></div>""<ul><li><div>Protein folding <strong>precisely positions catalytic amino acid residues</strong> in the active site.</div>
</li><li>
<div>This spatial arrangement <strong>eliminates unproductive collisions</strong> once the substrate is bound.</div>
</li><li>
<div>The <strong>enzyme’s structure</strong> can use distant parts of the polypeptide chain to <strong>anchor or orient the substrate</strong>.</div>
</li><li>
<div>Some enzymes have:</div>
<ul>
<li>
<div>A <strong>specificity subsite</strong> (for substrate recognition)</div>
</li>
<li>
<div>A <strong>reaction subsite</strong> (for actual catalysis)</div>
</li>
</ul>
</li><li>
<div>Changes to these residues can result in <strong>altered kinetic behavior</strong> or specificity.</div></li></ul>
"
"<div>What is the proximity (propinquity) factor and how does it affect reaction rates?</div>
<div></div>""<ul><li><div>The <strong>proximity factor</strong> (also called the <strong>propinquity factor</strong>) refers to the enzyme’s ability to <strong>bring substrates and catalytic groups close together</strong>.</div>
</li>
<li>
<div>By holding reactants in <strong>close spatial proximity</strong>, enzymes <strong>increase the likelihood of productive interactions</strong>.</div>
</li>
<li>
<div>This reduces the <strong>entropy barrier</strong> and enhances reaction rates—even without direct catalytic chemistry.</div>
</li>
<li>
<div>Some active sites function mainly through <strong>positioning and orientation</strong>, relying on proximity rather than covalent chemistry.</div>
</li>
</ul>
<div></div>"
What is the main reason 5' monophosphate decarboxylate is able to increase reaction by 10^17 fold ?&nbsp;It does ground state destabilzation which leads to transition state stabelization. Ground state destabilization refers to the <strong>lowering of the stability of the substrate's ground state</strong> (its normal, lowest-energy form) when it binds to the enzyme. This <strong>raises the relative energy</strong> of the ground state compared to the transition state, effectively <strong>lowering the activation energy (ΔG‡)</strong>.
"What does the following show&nbsp;<br><img src=""paste-5a607bf06f769f626644cfc590515f589eebba73.jpg"">""<div><span style=""font-weight: bold;"">Here is another example of a
lowering of the transition state energy and speeding up the reaction.&nbsp; By holding the substrate in an unstable
configuration halfway between the substrates and the products, the directed attack
on the substrate can be accomplished easily since everything is aligned. As a
result, the reaction is energetically more able to proceed.&nbsp;</span></div>"
"<div>What role does active site protection and conformational change play in enzyme catalysis?</div>
<div></div>""<ul><li><div>Many enzymes have <strong>multiple active sites</strong> that must be <strong>shielded from water</strong>, which can <strong>inactivate the enzyme</strong> (e.g., by hydrolyzing reactive intermediates).</div>
</li><li>
<div>Enzymes like <strong>citrate synthase</strong> use a <strong>flexible ""lid""</strong> that closes over the active site upon <strong>substrate binding</strong>, protecting it from water.</div>
</li><li>
<div>This <strong>lid formation</strong> is often the <strong>rate-limiting step</strong>, driven by conformational changes.</div></li></ul>
"
How are redox reactions structured"<div>A <strong>redox reaction</strong> involves <strong>electron transfer</strong> between two reactants:</div>
<ul>
<li>
<div>One <strong>donates electrons</strong> (oxidized)</div>
</li>
<li>
<div>One <strong>accepts electrons</strong> (reduced)</div></li></ul>"
"What are the hald cell reactions of the following overall redox reaction&nbsp;<br><img src=""Screen Shot 2025-04-30 at 3.36.30 PM.png"">""<img src=""Screen Shot 2025-04-30 at 3.37.00 PM.png"">"
"<div>What does the Nernst Equation calculate in biological and chemical systems?</div>
<div></div>""<ul><li><div><img src=""Screen Shot 2025-04-30 at 3.45.54 PM.png""></div>
</li><li><div>The <strong>Nernst Equation</strong> determines the <strong>actual reduction potential (ΔE)</strong>&nbsp;(a measure of a molecule's or ion’s tendency to <strong>gain electrons</strong> during a redox reaction)of a redox reaction under <strong>non-standard conditions</strong>.</div></li><li>
<div>It adjusts <strong>ΔE°</strong> (standard reduction potential) based on the <strong>concentration</strong> of oxidized and reduced species.</div>
</li><li>
<div>Important in <strong>cellular metabolism</strong>, <strong>electrochemistry</strong>, and <strong>electron transport chains</strong>.</div></li></ul>
"
"<div>How does redox potential relate to spontaneity and free energy? What does a negative standard potential mean and what does a positive stadard potential mean.&nbsp;</div>
<div></div>"<ul><li><strong>When ΔE is positive</strong>, <strong>ΔG is negative</strong> → the reaction is <strong>spontaneous</strong></li><li><div><strong>More negative E°</strong>: Species is a <strong>better electron donor</strong> (more likely to be oxidized):&nbsp; less potential to be reduced&nbsp;</div></li><li><strong>More positive E°</strong>: Species is a <strong>better electron acceptor</strong> (more likely to be reduced). : More potential to be redu ce</li></ul>
What does additon reactions and elimination reactions mainly indicate?&nbsp;"Addition
reactions add to double bonds, while elimination reactions eliminate groups to
form double bonds. In many cases water is tarsfered. In the below example fimerase double bond brakes with condensation.&nbsp;<br><img src=""paste-2d4fe497964cb005a2296a8f3607f40d5bd9a027.jpg""><br>"
"How are Esters, amides and acetals are
cleaved ?&nbsp;&nbsp;""<div>Esters, amides and acetals are
cleaved by a reaction with water and their formation requires the addition of
water. <u>C-N,
C-O, S-O, P-O and P-N are cleaved with a reaction that requires water as a
substrate</u>. In the diagram (a) peptide bond is
broken (b) phosphate ester is broken.</div><div><img src=""paste-8a8215b7c245d6e78219250931f2d05e7aa5ed8e.jpg""><br></div><div><div>A common strategy is to chemically
activate the substrate then react the activated compound.&nbsp; dNTPs are activated nucleotides that break
the ester phosphate bond driving the reaction forward by the free energy released
in the reaction.</div></div>"
What is the proccess of decarboxylation?"<div>Decarboxylation is <u>the loss of CO</u><u>2</u><u> </u>and is
a stable gas which when released drives the reaction forward with the help of cafacors like TPP&nbsp;</div><div><img src=""paste-eeac10546b1b9a84be7b8be21705c96cd226b9ef.jpg"" width=""1059""><br></div>"
"<div>What are the effects of enzymes altering the pKs of the substarte ?</div>
<div></div>""<ul><li><div>Enzymes can <strong>shift the pKₐ values</strong> of substrate groups within the <strong>active site</strong> to promote <strong>acid-base catalysis</strong>.</div>
</li><li>
<div>Example: A normally unreactive C–H bond (pKₐ ~20) can become acidic if the enzyme stabilizes the negative charge (e.g., via <strong>H-bonding to –OH</strong>).</div>
</li><li>
<div>Enzymes create a <strong>microenvironment</strong> that alters protonation behavior, making protons easier to <strong>donate or accept</strong> at neutral pH.</div></li></ul>
"
"<div>Describe how Glu35 and Asp52 in lysozyme work together using pKₐ manipulation.</div>
<div></div>""<ul><li><div><strong>Glu35</strong>: Normally has a pKₐ of 3.5 but is shifted to ~6 in lysozyme, so it is <strong>protonated at neutral pH</strong>, acting as a <strong>proton donor</strong>.</div>
</li><li>
<div><strong>Asp52</strong>: Retains a <strong>normal pKₐ</strong>, so it is <strong>ionized (negatively charged)</strong> at neutral pH and <strong>stabilizes the transition state</strong>.</div>
</li><li>
<div>This setup allows Glu35 to <strong>break the C–O bond</strong> in the substrate, while Asp52 stabilizes the <strong>positively charged carbocation</strong> formed.</div></li></ul><div><img src=""paste-281399f6f4eddc468726ec1b0494e2797aac2f75.jpg""><br></div>
"
"<div>What is burst kinetics in enzyme catalysis?</div>
<div></div>""<ul><li><div><strong><img src=""Screen Shot 2025-04-30 at 4.15.51 PM.png"" width=""665""></strong></div>
</li><li><div><strong>Burst kinetics</strong> occurs when an enzyme forms a <strong>stable intermediate</strong> quickly, followed by a <strong>slower rate-limiting step</strong> to release product.</div></li><li>
<div>The <strong>initial fast phase</strong> corresponds to rapid turnover until the enzyme becomes saturated with the intermediate.</div>
</li><li>
<div>Afterward, the reaction proceeds at a <strong>slower, steady-state rate</strong>.</div></li></ul><div><br></div>
"
"<div>Why does chymotrypsin display burst kinetics?</div>
<div></div>""<ul><li><div>Cymotrypsin has a <strong>catalytic triad</strong> (Asp102, His57, Ser195) that rapidly forms a <strong>tetrahedral intermediate</strong>.</div>
</li><li>
<div>The <strong>acyl-enzyme intermediate</strong> forms quickly upon peptide bond cleavage.</div>
</li><li>
<div>However, the <strong>release of the second peptide fragment (C-terminus)</strong> is slower and becomes the <strong>rate-limiting step</strong>.</div>
</li><li>
<div>The result is an <strong>initial burst of product</strong>, followed by slower product formation.</div></li><li><div><img alt=""Chymotrypsin - an overview | ScienceDirect Topics"" src=""3-s2.0-B9780123809247100018-gr3.jpg""><br></div></li><li><div>The <strong>oxyanion hole</strong> stabilizes the high-energy intermediate, contributing to fast formation but slower breakdown.<br></div></li></ul>
"
"<img src=""Screen Shot 2025-04-30 at 4.15.51 PM.png""><br>What does the following graph show?&nbsp;<br>""<ul><li><div>The graph shows a <strong>rapid initial increase</strong> in product formation - burst phase- limited by the <strong>amount of enzyme</strong>.</div>
</li><li>
<div>Followed by a <strong>linear, slower phase</strong>, reflecting the <strong>rate-limiting release</strong> of product.</div>
</li><li>
<div>If a <strong>colored product</strong> (e.g., yellow from dinitrophenyl ester) is monitored, the color appears quickly then increases steadily.</div></li></ul>
"
"<div>What are bifunctional or multifunctional enzymes?</div>
<div></div>""<ul><li><div>These enzymes can <strong>catalyze more than one distinct chemical reaction</strong>.</div>
</li><li>
<div>They often play roles in <strong>metabolic efficiency</strong>, allowing sequential steps to occur without releasing intermediates.</div>
</li><li>
<div>They can perform reactions in <strong>a single site</strong> or in <strong>multiple connected domains</strong>.</div></li></ul>
"
What are the three classes of multifunctional enzyme mechanisms?"<ol><li><div><strong>Single active site</strong> catalyzing <strong>two reactions</strong></div>
</li>
<li>
<div><strong>Two separate reactions</strong> at <strong>two distant active sites</strong> on the same protein (distinct domains).</div>
</li>
<li>
<div><strong>Two separate reactions</strong> at active sites <strong>connected by a tunnel</strong>, guiding the intermediate directly.</div>
</li>
</ol>
<div></div>"
What type of multifunctional calss is tryptophan synthase an example of ?"<img src=""paste-157eabd011b20f9bc626adfaad04c339b0ae138b.jpg""><br>The third kind: Tunnel Protein&nbsp;"
Provide the following for First Order Kinetics&nbsp;<br>Differential Rate Law :<br>Integrated Rate Law:&nbsp;<br>Straight iline plot to determine rate constant :&nbsp;<br>Slop of straight line plot&nbsp;<br>Half-Life:&nbsp;<br>Units of K&nbsp;"<img src=""Screen Shot 2025-04-30 at 9.08.11 PM.png"">"
Provide the following for 2nd Order Kinetics&nbsp;<br>Differential Rate Law :<br>Integrated Rate Law:&nbsp;<br>Straight iline plot to determine rate constant :&nbsp;<br>Slop of straight line plot&nbsp;<br>Half-Life:&nbsp;<br>Units of K&nbsp;"<img src=""Screen Shot 2025-04-30 at 9.09.46 PM.png"">›"
What does ΔG‡ represent in a reaction energy diagram?"ΔG‡ is the Gibbs free energy of activation – the energy barrier between reactants and products.<br><img src=""paste-2505b6cf034bccb4abbc5738a7c8044d96f4cebb.jpg"">"
How does ΔG‡ affect the reaction rate?"A higher ΔG‡ means a slower reaction. A lower ΔG‡ means a faster reaction.<br><img alt=""How to Interpret Thermodynamics of Reactions"" src=""Asset-2.png""><br><img src=""paste-f241d5b752afe24c8759c4dce3427320990ad7fb.jpg"" width=""721""><br>"
"<div style=""text-align: center;"">What does the expression</div><div style=""text-align: center;""><img src=""Screen Shot 2025-04-30 at 9.19.31 PM.png""></div><div style=""text-align: center;"">mean physically&nbsp;</div>"It shows that increasing temperature or decreasing ΔG‡ increases the reaction rate. The reaction speeds up when thermal energy is added.
What is the rate limiting step in the green vs red? Which graph shows burst kinetics?&nbsp;"<img src=""paste-f4be8ced8c5100a88986bf2d90f45977154c128b.jpg"" width=""608""><br>Green : A-&gt; I Limiting step&nbsp;<br>Red: I-&gt;P Limiting Step ( BURST KINETICS)"
How do enzymes catalysis affect activation energy?&nbsp;"A catalyst lowers the activation energy (ΔG‡), making the reaction proceed faster. The change in activation energy is depicted as (ΔΔG‡)<br><img src=""paste-94d20bf9912849c8fc7f461108232bd145fdbb88.jpg"">"
What is the mathematical expression for the rate enhancement by a catalyst which includes&nbsp;ΔΔG‡₍cat?"<img src=""paste-9dfc248eac625e5766d3663376ce3fa044f30950.jpg""><br>RT= 2.48"
What does a ΔΔG‡₍cat₎ of 5.71 kJ/mol correspond to in rate enhancement?"<img src=""IMG_83095871F82F-1.jpeg"">What does a ΔΔG‡₍cat₎ of 5.71 kJ/mol correspond to in rate enhancement?<br>"
What order kinetic do enzymes follow when substrate conentrations are high?&nbsp;"Enzymes
follow zero order kinetics when substrate concentrations are high.&nbsp; Zero order means there is no increase in the
rate of the reaction when more substrate is added ( plateu)"
What is the basic enzyme reaction model in Michaelis-Menten kinetics and what is the assumption?&nbsp;"<img src=""paste-c14f1f951d399fabfb02798da84ec9a9f706329c.jpg""><br><div><span style=""font-weight: bold;"">Assumption of equilibrium</span></div>
<div><span style=""font-weight: bold;"">&nbsp; k</span><span style=""font-weight: bold;"">-1</span><span style=""font-weight: bold;"">&gt;&gt;k</span><span style=""font-weight: bold;"">2</span><span style=""font-weight: bold;""> the formation of product is so
much slower than the formation of the ES complex. </span><span style=""font-weight: bold;"">When the substrate concentration becomes large enough to force the
equilibrium to form completely all ES the second step in the reaction becomes
rate limiting because no more ES can be made and the enzyme-substrate complex
is at its maximum value</span></div><div><span style=""font-weight: bold;""><br></span></div><div><span style=""font-weight: bold;"">We can assume:&nbsp;</span><span style=""font-weight: bold;"">K</span><span style=""font-weight: bold;"">s</span><span style=""font-weight: bold;""> is
the dissociation constant for the ES complex.</span><img src=""paste-8ea09b791c6b9f7616651874c31d0e97cdd24eb7.jpg""></div>"
What is the steady-state assumption?"The concentration of the ES complex remains constant: d[ES]/dt ≈ 0 during the initial phase.<br><img src=""paste-95077690a03a7b0e40bae82afc05e8c9b9ef17d2.jpg""><br><ul><li><div>This allows us to simplify the rate equations and derive a manageable expression for reaction velocity.</div>
</li>
<li>
<div>Without it, solving for [ES][ES][ES] would require solving complex differential equations involving time.</div>
</li>
<li>
<div>It provides the foundation for the <strong>Michaelis-Menten equation</strong>, which relates initial reaction velocity v0v_0v0​ to substrate concentration [S][S][S].</div>
</li></ul>"
What equation represents enzyme conservation necesarry for the derivation of&nbsp;Michaelis eqtn[E]ₜ = [E] + [ES], where [E]ₜ is the total enzyme concentration. (mainly E and ES since little product formed- mainly worried at the bigenning of the rxn)
"<div><span style=""font-weight: bold;"">The Michaelis - Menten equation</span></div>""<img src=""paste-be021a129c294ceac0837331f8afa36ee0edb606.jpg""><br>Initial velocity depends on substrate concentration [S], the total enzyme [E]ₜ, and rate constants through Kₘ."
What does Vmax = in the michaelis-Menten equation ?&nbsp;"<img src=""Screen Shot 2025-04-30 at 9.51.32 PM.png"">"
What is the Michaelis constant (Km) and what does it represent?"Kmis the substrate concentration at which the reaction rate is half of Km. It reflects the enzyme’s affinity for the substrate Km&nbsp;means higher affinity.<br><img src=""paste-eb439ce50bb1f90b4397ccd912d7ff8fb3ce9c71.jpg"">"
How can Km be expressed in terms of rate constants?"<img src=""Screen Shot 2025-04-30 at 9.56.02 PM.png"">\<br>This is the sum of the rate constants for ES breakdown divided by the rate of ES formation.<br>"
What is the lineweaver-burk pot&nbsp;"<img src=""Screen Shot 2025-04-30 at 9.59.56 PM.png"" width=""1060"">"
what does the slope, y-inercept, and x intercept give from the Linewaver-Burk plot?"<img src=""Screen Shot 2025-04-30 at 10.01.54 PM.png""><br><img src=""paste-83c073037b6fd5f6c28dd2dc98c4381df8842e18.jpg"">"
What are the limitations to&nbsp;Lineweaver–Burk Plot Is Important ?"<ul><li><div>❌ Overemphasizes data at low substrate concentrations (can distort accuracy).</div>
</li><li>
<div>📈 Experimental error in low-[S] values affects the line more than in high-[S] data.</div></li></ul>
"
What is kcₐₜ and what does it represent?"<ul><li><div><strong>kcₐₜ = Vₘₐₓ / [E]ₜ</strong></div>
</li><li>
<div>Called the <strong>turnover number</strong></div>
</li><li>
<div>Represents how many substrate molecules one enzyme molecule can convert to product <strong>per second</strong> when saturated</div>
</li><li>
<div>A key measure of <strong>enzyme catalytic power</strong></div></li></ul>
"
What is catalytic perfection?"<ul><li><div>Achieved when every substrate molecule that binds results in product formation</div>
</li><li>
<div>Mathematically: <strong>kcₐₜ/Kₘ = k₁</strong></div>
</li><li>
<div>Diffusion-controlled limit: <strong>10⁸ – 10⁹ M⁻¹s⁻¹</strong></div>
</li><li>
<div>Enzyme operates at the maximum possible rate, as fast as <strong>molecular collisions</strong> allow</div></li></ul>
"
What does the follow bi-substrate graph tell you about the order of binding and reaction?&nbsp;<br>"<img src=""paste-7dd709e7db6262c0545b6a80998e24d26feecfb2.jpg"" width=""782""><br><div>This diagram represents an ordered reaction where A must bind first
before B, then the reaction occurs
and P comes off before Q</div>"
"What does the follow bi-substrate graph tell you about the order of binding and reaction?&nbsp;<br><img src=""paste-28c2feeab608d93419fa52cc6b3e1c293602e413.jpg"" width=""712"">""<div>Random binding and release can follow any path. Either A or B binds
first while P or Q can come off first.</div>"
"<img src=""paste-587eda5de12e6bca361f4b3282ef04668f1f0192.jpg""><br>What does the follow bi-substrate graph tell you about the order of binding and reaction?&nbsp;""<div>Ping-Pong indicates that one substrate comes on and modifies the enzyme
and the product leaves before the other substrate binds. Here F is the
covalently modified enzyme</div>"
<div><div><div><div><div><div><div><div><div>What are the three types of inhibition kinetics&nbsp;</div></div></div></div></div><div><div></div></div></div></div></div></div><ol><li>Competitive Inhibition: Inhibitor competes with the substrate for the <strong>active site</strong> of the enzyme.</li><li>Uncompetetive Inhibition: Inhibitor binds only to the enzyme-substarte (ES) complex, not the free enzyme&nbsp;</li><li>Noncompetetive (mixed) inhibition: Inhibitor binds to both the free enzyme and the ES comples ( at a site other than the active site)</li></ol>
In competetive inhibition what does the stregth of the inhibition depend on?&nbsp;"<img src=""paste-c5ca8b4af3fe660fa249048260c7b2504959d67a.jpg"" width=""582""><br><span style=""font-weight: bold;"">The strength of inhibition depends on the dissocotiation constant KI - Small Ki means stringer binding because there is less free enzyme and inhibitor- most are in the complex.&nbsp;</span><span style=""font-weight: bold;""><br></span><span style=""font-weight: bold;""></span><img src=""paste-a85e7e7c316651fc093c0fa169a38c3798cdb7f8.jpg"" width=""407"">"
"<img src=""Screen Shot 2025-04-30 at 10.55.21 PM.png""><br>What does the following equations tell you about the effects of&nbsp; competetive inhibition on Vmax and Km?&nbsp;<br>""<ul><li><div><strong>The term&nbsp;</strong>αaccounts for the presence of inhibitor. Shows how inhibitor concentration and its affinity (Ki) impact apparent Km. Higer [I] or lower KI means larger α and thus greater inhibition</div></li></ul><div>OVERALL :&nbsp;</div><ul><li><div><strong>Effect on Vmax</strong>: <strong>Unchanged</strong> (can be overcome with excess substrate).<br></div></li><li>
<div><strong>Effect on Km</strong>: <strong>Increases</strong> (more substrate is needed to reach ½ Vmax).</div></li></ul><div><br></div>
"
"<img src=""paste-b414e3f14cbf66a377448b579608ea9ab838e2ca.jpg""><br>What is the following graph showing?""<img src=""Screen Shot 2025-04-30 at 11.02.57 PM.png""><br>This graph shows the <strong>Michaelis-Menten curves</strong> for an enzyme-catalyzed reaction under <strong>increasing concentrations of a competitive inhibitor</strong>.&nbsp;<br><br>"
"What does the following Lineweaver-Burk Plot Show<br><img src=""paste-c3520092132b0768fff7f893090a76146c013f7a.jpg"" width=""864"">""<div>This plot confirms <strong>competitive inhibition</strong> because:</div>
<ul>
<li>
<div><strong>Only KM​ increases</strong> (apparent substrate affinity decreases)</div>
</li>
<li>
<div><strong>Vmax remains unchanged</strong></div>
</li>
<li>
<div>The inhibitor competes with the substrate for the <strong>same active site</strong></div>
</li>
</ul>
<div></div>"
How can competetive inhibition be overcome?Competitive inhibition can be overcome by <strong>increasing substrate concentration</strong>, which restores the reaction rate.
What is the effects of uncompetitive inhibtion on Vmax and Km and how does it show up on lineweiver-burk plot"<ul><li><div><strong><img src=""paste-b0f2099d8aba9c53679a3df7a348d0115080603b.jpg"">Effect on Vmax</strong>: <strong>Decreases</strong> (less active enzyme complex available).</div>
</li><li>
<div><strong>Effect on Km</strong>: <strong>Decreases</strong> (apparent affinity increases).</div></li><li><div><div><strong>Lineweaver-Burk Plot</strong>:</div>
<ul>
<li>
<div><strong>Parallel lines</strong>.</div>
</li>
<li>
<div>Both y- and x-intercepts shift.</div></li></ul></div></li></ul>
"
"<div style=""text-align: center;"">WHat does the following show</div><div style=""text-align: center;""><img src=""paste-7c17fb70ddc284c26814b60711cf08748b860154.jpg"" width=""852""></div>"Noncompetitive (Mixed) Inhibition
Whata re the effects on Vmax and Km of Noncompetitive (Mixed) Inhibition and how does this show up on linear graph ?"<ul><li><div><strong>Effect on Vmax</strong>: <strong>Decreases</strong> (some enzyme is always inactive).</div>
</li>
<li>
<div><strong>Effect on Km</strong>:</div>
<ul>
<li>
<div><strong>Unchanged</strong> in <strong>pure noncompetitive inhibition</strong>.</div>
</li>
<li>
<div><strong>Varies</strong> in <strong>mixed inhibition</strong> (can increase or decrease depending on binding preferences).</div>
</li>
</ul>
</li>
<li>
<div><strong>Lineweaver-Burk Plot</strong>:</div>
</li><ul>
<li>
<div>Lines intersect <strong>left of the y-axis</strong> (not on either axis).</div></li>
</ul>
</ul><div><img alt=""Enzyme inhibition and kinetics graphs ..."" src=""paste-4e0237f7ee9fdb7cb0e66103bcf92b8bd6135fd3.png"" width=""858""><br></div>"
What is&nbsp;<strong>random bi-reactant mechanism ?&nbsp;</strong>"<div>If the order of substrate binding or product release <strong>doesn’t matter</strong>, it is called a <strong>random bi-reactant mechanism</strong>.</div>
<ul>
<li>
<div>Both A and B can bind in any order.</div>
</li>
<li>
<div>Both P and Q can be released in any order.</div></li></ul><div><img src=""Screen Shot 2025-04-30 at 11.48.08 PM.png""><br></div>"
Ping-Pong Mechanism"E+A⇌ EA ⇌ FP ⇌ P+F then F+B ⇌ FB ⇌ EQ ⇌ Q+E<br><ul><li><div><strong>E and F</strong> are two <strong>different forms</strong> of the same enzyme.</div>
</li><li>
<div>One product (P) is released <strong>before</strong> the second substrate (B) binds.</div>
</li><li>
<div>Common in enzymes like <strong>transaminases, transacylases</strong>, and <strong>transphosphorylases</strong>.</div></li></ul>
"
What does&nbsp;Uni, Bi, Ter, Quad indicate in multi-substrate kinetics?&nbsp;"<div><strong>ni, Bi, Ter, Quad</strong> = indicate <strong>number of substrates/products</strong> involved:</div>
<ul>
<li>
<div><strong>Uni</strong> = 1 substrate</div>
</li>
<li>
<div><strong>Bi</strong> = 2 substrates</div>
</li>
<li>
<div><strong>Ter</strong> = 3 substrates</div>
</li>
<li>
<div><strong>Quad</strong> = 4 substrates</div></li></ul>"
How can you simplify the analysis of a two-substrate enzyme reaction?By holding one substrate constant and varying the other to calculate <strong>Km</strong> and <strong>Vmax</strong> for each substrate individually. Keep increasing B while measuring Vmax for A, then <strong>plot Vmax vs. B concentration</strong> to extrapolate the true Vmax for A.&nbsp;
What kind of reaction does the method of varying one substrate while keeping the other constant work best for?A simple <strong>ordered Bi-Bi reaction</strong>, where both substrates must bind in a specific sequence.
Ping Pong Bi-Bi Mechanism&nbsp;"<img src=""Screen Shot 2025-05-01 at 12.02.29 AM.png"" width=""832""><br>"
Uni-Uni-Uni Ping Pong"<strong>""Uni-Uni-Uni""</strong> = sequential reactions where one substrate is acted on at a time, but the enzyme keeps cycling through intermediate form<br><img src=""Screen Shot 2025-05-01 at 12.04.45 AM.png"" width=""859"">"
<strong>Q:</strong> In a Ping Pong Bi Bi reaction, which substrate binds to which enzyme form?<div><strong>A:</strong> Substrate A binds to enzyme <strong>E</strong>, and substrate B binds to the modified enzyme <strong>F</strong>.</div>
"What does the following graphs show?&nbsp;<img src=""Screen Shot 2025-05-01 at 12.40.17 AM.png"">"Pink Pong Bi Bi Mechanisms - This pattern of <strong>parallel lines</strong> is <strong>distinctive</strong> for Ping Pong Bi Bi kinetics and <strong>diagnostically different</strong> from Ordered Bi Bi, which shows intersecting lines
"<strong>Q:</strong> Why do the <strong>intercepts</strong> change on Lineweaver-Burk plots in Ping Pong Bi Bi kinetics?<br><img src=""Screen Shot 2025-05-01 at 12.40.17 AM.png"">"<div><strong>A:</strong> Because substrates A and B bind to different enzyme forms (E and F), affecting the apparent <strong>Vmax</strong>.</div>
"<img src=""Screen Shot 2025-05-01 at 12.40.17 AM.png""><strong>:</strong> Why do the <strong>slopes</strong> remain the same in the Lineweaver-Burk plots of Ping Pong Bi Bi kinetics?"The slopes remain constant because the binding of A and B is <strong>irreversible</strong> after product P is released.
WHat is a sequential Bi Bi mechanism ?"<div>In a <strong>sequential Bi Bi</strong> mechanism:</div>
<ul>
<li>
<div>Both <strong>substrates A and B must bind</strong> to the enzyme <strong>before</strong> any product is released.</div>
</li>
<li>
<div>The formation of a <strong>ternary complex (EAB)</strong> is required before catalysis can proceed.</div></li></ul>"
Two types of Bi-Bi mechanism?&nbsp;"<div style=""display: inline !important;""><strong><img src=""Screen Shot 2025-05-01 at 12.47.37 AM.png"">1. Ordered Sequential</strong>:</div><ul><li><div>Substrates bind in a <strong>specific order</strong> (e.g., A must bind before B).</div></li></ul><ol>
<li>
<div><strong>Random Sequential</strong>:</div>
<ul>
<li>
<div>Either A or B can bind first; <strong>no strict order</strong>.</div></li>
</ul>
</li></ol>"
"<img src=""Screen Shot 2025-05-01 at 12.50.43 AM.png""><br>What is being done in this graph ?&nbsp;"Sequentoal Bi Bi mechanism -&nbsp;<strong>Intersecting lines</strong>, typically to the left of the y-axis, indicating changes in both slope and intercept are indicative of a sequential Bi Bi mechanism
Why do slopes and intercepts change in the Lineweaver-Burk plots for Sequential Bi Bi reactions?"&nbsp;Because the binding of A and B is <strong data-end=""1088"" data-start=""1074"">reversible</strong>, and they bind to different enzyme forms (E, EA, EB, etc.)."
How can you distinguish between Sequential Bi Bi and Ping Pong Bi Bi using Lineweaver-Burk plots?<strong>A:</strong> Sequential shows <strong>intersecting lines</strong>; Ping Pong shows <strong>parallel lines</strong> when varying one substrate at different fixed concentrations of the other
What are dead-end complexes?&nbsp;"<div>Sometimes, products or substrates bind in
a way that <span style=""font-weight: bold;"">prevents
the reaction from proceeding</span>, forming a <span style=""font-weight: bold;"">dead-end
complex</span>.
These are important in <span style=""font-weight: bold;"">product inhibition studies</span>.</div><div><div><span style=""font-weight: bold;"">Examples shown:</span></div>
<div>•<span style=""font-weight: bold;"">Q
+ B</span>
bound together = Dead-end (no catalysis occurs)</div>
<div>•<span style=""font-weight: bold;"">A
+ P</span>
bound = Dead-end (mimics a false substrate-product combo)</div>
<div>•In
both cases, <span style=""font-weight: bold;"">no chemistry happens</span> —
the enzyme is “stuck” and inactive.</div></div><div><br></div><div><img src=""paste-e919e65a1f30821b7ecf05b26f5207c934c0f77b.jpg"" width=""748""><br></div>"
"<img src=""paste-0564d4a726ea38743e869652c6d0fc550d8f8741.jpg"" width=""659""><br><span style=""font-weight: bold;"">Which shows more effective
inhibition at lower concentrations? between 2 and 3&nbsp;</span>""<ol><li><div><strong>Linear</strong>:​<br>
→ Inhibition increases <strong>proportionally</strong> with [I]</div>
</li>
<li>
<div><strong>Parabolic</strong>:​<br>
→ Inhibition increases <strong>more sharply at higher concentrations</strong> (quadratic component)</div>
</li>
<li>
<div><strong>Hyperbolic</strong>:​<br>
→ Inhibition increases rapidly at <strong>low concentrations</strong>, then <strong>plateaus</strong> (most efficient at low [I])</div>
</li>
</ol>
<h3>&nbsp;Bottom takeaway:</h3>
<ul>
<li>
<div><strong>Curve 3 (Hyperbolic)</strong> shows the <strong>most effective inhibition at low concentrations</strong>.</div>
</li>
<li>
<div>Curve 2 (Parabolic) overtakes Curve 3 only at higher [I].</div>
</li></ul>"
"<img src=""paste-d0c86c2070cc83f326364555d8e546cdd1f96495.jpg"" width=""607""><br><span style=""font-weight: bold;"">W</span><span style=""font-weight: bold;"">hy</span><span style=""font-weight: bold;""> does the inhibition change at different
inhibitor concentrations???</span>""<div>These represent <strong>complex inhibition kinetics</strong> where inhibitors:</div>
<ul>
<li>
<div>Bind multiple sites</div>
</li>
<li>
<div>Affect Vmax and Km to different extents</div>
</li>
<li>
<div>Possibly form intermediate/inactive complexes</div></li></ul>"
"<img src=""paste-23194941b3871d4ade3928b8ab79e53741e4c8a4.jpg""><br>What does the following graph show you about the ASST-catalyzed sulfhufryl transfer from MUS (4-methylumbelliferyl sulfate)&nbsp; the donor to phenol to yield sulfonated phenol""<div><ul><li>This
plot shows initial velocity (v) of the ASST reaction at different fixed
concentrations of MUS (10–160 µM), while varying [phenol].</li><li>The
colors correspond to different MUS concentrations (blue = 10 µM, cyan = 160
µM).</li><li><span style=""font-weight: bold;"">Interpretation:</span>The
shape of the curves and <span style=""font-weight: bold;"">parallel lines in the Lineweaver-Burk
plot</span>
(inset) confirm a <span style=""font-weight: bold;"">ping-pong mechanism</span>.</li></ul><ul><li>This
is seen as the MUS concentration changes but lines remain parallel at low
phenol.</li><li>At <span style=""font-weight: bold;"">high
phenol concentrations</span>,
you see <span style=""font-weight: bold;"">substrate
inhibition</span>—reaction
slows down, as phenol begins to inhibit the enzyme.</li><li>These
parameters support a <span style=""font-weight: bold;"">ping-pong bi-bi kinetic model</span> with
<span style=""font-weight: bold;"">substrate
inhibition</span> by
phenol.</li></ul></div>
"
"From the conclusions of this graph what can you infer the mechanism of arysulfate sulfotransferase&nbsp; is for the substrates phenol?<br><img src=""paste-23194941b3871d4ade3928b8ab79e53741e4c8a4.jpg"">""<div><span style=""font-weight: bold;"">Ping-Pong Evidence:</span></div>
<div>•One
substrate (PNS) binds and product (p-nitrophenylate)
leaves before the second substrate (phenol) binds — consistent with <span style=""font-weight: bold;"">ping-pong
bi-bi kinetics</span>.</div><div><div>1.<span style=""font-weight: bold;"">Activation
Step:</span></div>
<div><ul><li><span style=""font-weight: bold;"">His436</span> (a
histidine residue in the enzyme) uses its lone pair to attack the <span style=""font-weight: bold;"">sulfur
atom</span> of
the aryl sulfate donor (e.g., PNS), forming a <span style=""font-weight: bold;"">covalent </span><span style=""font-weight: bold;"">sulfo</span><span style=""font-weight: bold;"">-histidine
intermediate</span>..This releases <span style=""font-weight: bold;"">p-</span><span style=""font-weight: bold;"">nitrophenylate</span> (PNS
minus the sulfuryl group).</li></ul></div>
<div>2.<span style=""font-weight: bold;"">Transfer
Step:</span></div>
<div><ul><li>.After PNS leaves, <span style=""font-weight: bold;"">phenol</span>
binds to the enzyme.</li><li>The <span style=""font-weight: bold;"">phenolate oxygen</span>
(deprotonated phenol) then nucleophilically
attacks the sulfur on the sulfo-histidine intermediate.</li><li>3.This yields <span style=""font-weight: bold;"">phenyl
sulfate</span>
(sulfonated phenol) and regenerates His436.</li></ul><div><img src=""paste-3b22dbe30458d82ce511d23d248f2ba59aba87ca.jpg"" width=""796""><br></div></div>
</div>"
What is the difference between ionic and coordinate covalent interactions in metal ion bonding?"Ionic interactions involve electrostatic attraction (common in group I-Na+ and K+/II&nbsp; Mg++ and Ca++metals), while coordinate covalent bonds occur when both electrons in a bond come from the same atom (e.g., Lewis base to Lewis acid), resulting in covalent-like properties.<br><img alt=""Ionic bond ,Covalent bond and Coordinate bond | Chemistry Types of Chemical Bonds | One Shot - YouTube"" src=""maxresdefault.jpg"">"
<strong>Q:</strong> How do P and D orbitals contribute to metal-ligand bonding in transition metals?"Transition metals use hybridization of P and D orbitals to form various geometries, enabling coordination with 2-electron donating ligands and achieving stable electron configurations.<br><div>In the P orbitals, the shared electrons
are maximizing the total of eight valiant electrons as seen below&nbsp;</div><div><img src=""paste-23c460e7182b9c4961aacec8f171e751c7915239.jpg"" width=""1119""><br></div>"
What does the Irving-Williams series describe, and what is the order of metal ion binding strength to organic molecules?he Irving-Williams series describes the natural order of <strong>stability of metal ion complexes</strong> with organic ligands. The order from <strong>strongest to weakest binders</strong> is:<br>(Cu²⁺ ≈ Zn²⁺ )&gt; (Ni²⁺ ≈ Co²⁺) &gt; (Fe²⁺ ≈ Mn²⁺) &gt; (Ca²⁺ ≈ Mg²⁺)
<div><div><div><div><div><div><div><div><div>What are usually the donor ligands in metaloproteins?&nbsp;</div></div></div></div></div></div></div></div></div>"<img src=""Screen Shot 2025-05-01 at 12.48.26 PM.png"">"
Which metals are most commonly found in proteins based on frequency?"Magnesium (16%), Zinc (9%), Iron (8%), and Manganese (6%).<br><img src=""paste-300aa3564a50698520cbde3644f77b3e6924fcd7.jpg"" width=""1003"">"
<strong>Q:</strong> What is the role of hemoglobin and what metal does it associate with?"<img src=""Screen Shot 2025-05-01 at 12.53.24 PM.png""><br>Hemoglobin carries O₂ in blood, increasing its solubility ~70-fold, and uses <strong>Fe²⁺ (ferrous iron)</strong> in a heme group; oxygen binding is cooperative across its 4 subunits.<br>"
What is the reaction in hemaglobin with Fe3+ ?"<div><img src=""paste-313d9db5d2f92869bcd9f02801740f3f407a5c27.jpg"" width=""930""></div><div>•Fe+2 form&nbsp;
Low spin state in oxygenated form (diamagnetic) where iron is in the
plane of the heme.</div>
<div>•High
spin state in deoxy
state (paramagnetic) where iron is out of the plane of the heme.</div>"
What distinguishes myoglobin from hemoglobin?Myoglobin is a <strong>single-subunit</strong> oxygen storage protein in muscle; it binds O₂ with no cooperative effects.
What is hemerythrin, and where is it found?"<img src=""Screen Shot 2025-05-01 at 12.58.34 PM.png"" width=""1081"">emerythrin is an oxygen-binding protein found in <strong>marine invertebrates and methanotrophic bacteria (methane producing)</strong>, using 2&nbsp;<strong>Fe³⁺</strong> and binding oxygen as a <strong>hydroperoxide</strong>.<br>&nbsp;"
What makes hemocyanin different from hemoglobin?Hemocyanin uses <strong>copper</strong> (not iron) to bind O₂, found in <strong>mollusks and arthropods</strong>, functions well in <strong>cold, low-O₂ environments</strong>, and shows <strong>cooperative binding</strong>.
What is the structure of hemocyanin?"It is a <strong>dimer or hexamer</strong> (species dependent), with <strong>two Cu atoms per binding site</strong>, and is <strong>homologous to phenol oxidases</strong>.<br><img src=""paste-ba45c22d5e3694ccbc689a11ba8f3741f93d4e10.jpg"" width=""755""><br>"
What is the function, location and structure of chlorocruorin and erythrocruorin ?"<ul><li><div><strong><img src=""Screen Shot 2025-05-01 at 1.03.41 PM.png""></strong></div>
</li><li><div><strong>Function:</strong> Oxygen-binding proteins</div></li>
<li>
<div><strong>Location:</strong> Found in <strong>annelids</strong> (e.g., earthworms)</div>
</li>
<li>
<div><strong>Structure:</strong> Very large, <strong>multi-subunit complexes</strong> (16–17 kDa subunits) &nbsp;they are <strong>free-floating in plasma containing heme groups with Fe2+ binding to oxygen&nbsp;</strong></div>
</li></ul>"
What is the function of cytochromes and what conditions are they typically found in?<div></div>romes and what are the different hemes invovled in cytochroneme?&nbsp;<br>Cytochromes are heme-containing proteins that transfer electrons via <strong>Fe²⁺ ⇌ Fe³⁺</strong> redox cycling. They are commonly found under <strong>aerobic conditions</strong> and vary by heme type (a, b, c, o), which affects their redox potential and structure
Which Heme is&nbsp; covelantly bound to proteins and which hemes only associate?&nbsp;"<img src=""Screen Shot 2025-05-01 at 1.07.53 PM.png"">"
What is the structure and function of rubredoxin?"Rubredoxin is a simple iron-sulfur protein with <strong>one Fe²⁺/Fe³⁺</strong> coordinated by <strong>4 cysteine residues</strong>. It acts as an <strong>electron carrier</strong> and is always in a <strong>high spin state</strong>. Found in sulfur-metabolizing <strong>bacteria and archaea</strong>.<br><img src=""paste-a55abb027853edca7b9ea720db68ad56146efeaf.jpg"" width=""901"">"
What is the structure and function of ferredoxins?<div>Ferredoxins are <strong>iron-sulfur proteins</strong> that function as <strong>electron carriers</strong> in biological redox reactions.&nbsp;</div><div>There are different ferredoxin cluster structures :&nbsp;</div><div>(2Fe-2S) cluster and 4Fe-4S cluster&nbsp;</div>
What are the types and roles of ferredoxins (2Fe–2S)?"<div>Ferredoxins contain <strong>2Fe–2S clusters</strong>, often found in:</div>
<ul>
<li>
<div><strong>Plant-type</strong> (photosynthesis)</div>
</li>
<li>
<div><strong>Thioredoxin-type</strong> (nitrogenase related)</div>
</li>
<li>
<div><strong>Adrenodoxin-type</strong> (electron transfer to cytochrome P450)</div>
</li>
<li>
<div>Function involves <strong>Fe³⁺–Fe³⁺ ⇌ Fe²⁺–Fe³⁺</strong> redox cycling, usually <strong>diamagnetic</strong> despite having unpaired electrons due to orbital pairing.</div></li></ul>"
What is the structure of 4Fe–4S ferredoxins, and what are their redox states?"<div><img src=""Screen Shot 2025-05-01 at 1.13.36 PM.png"">4Fe–4S clusters have cube-like structures, shifting between:</div>
<ul>
<li>
<div><strong>Low potential forms</strong>: [2Fe³⁺, 2Fe²⁺] or [1Fe³⁺, 3Fe²⁺]</div>
</li>
<li>
<div><strong>High potential forms</strong>: [3Fe³⁺, 1Fe²⁺] or [2Fe³⁺, 2Fe²⁺]<br>
These clusters <strong>transfer electrons</strong> and are abundant in <strong>anaerobic bacteria</strong>, photosystem I, and mitochondrial NADH dehydrogenase.</div></li></ul><div><br></div>"
What is the structure and function of ferritin?Ferritin is a <strong>universal iron storage protein</strong> that stores <strong>Fe³⁺</strong> and protects cells from iron toxicity. It keeps iron in a safe, soluble form and its levels are <strong>diagnostic for iron deficiency</strong>. Levels decrease during infection to <strong>limit iron availability to pathogens</strong>.
"<div><strong>Q</strong>What is transferrin and how does it transport iron?</div>
<div></div>"<div>Transferrin is a <strong>glycoprotein in plasma</strong> that binds <strong>Fe³⁺</strong> tightly (Ka ≈ 10²³ M⁻¹), carries <strong>2 Fe³⁺ per molecule</strong>, and delivers iron to cells via <strong>receptor-mediated endocytosis</strong>. It binds iron using <strong>Tyr, His, and Asp</strong> residues. There is <strong>no excretion mechanism</strong>, so transfusions can cause <strong>iron overload</strong>.</div>
What is the role of ceruloplasmin?Ceruloplasmin is a <strong>copper storage protein</strong> found in the <strong>blood</strong>, important for <strong>copper transport and regulation</strong>.
What is the function and active site composition of carbonic anhydrase?"Carbonic anhydrase catalyzes the reversible hydration of <strong>CO₂ + H₂O ⇌ H₂CO₃</strong>.<br>
Its active site contains <strong>Zn²⁺</strong> coordinated to <strong>three histidines and a water molecule</strong>. A fourth histidine acts as a <strong>base</strong>, removing a proton and forming a <strong>Zn-bound OH⁻</strong>, forming an electrophile that then attacks CO₂.<br><img src=""paste-e357648007d481ac761a883b7d5163208740bb7f.jpg"" width=""993"">"
What metal and structure are involved in Vitamin B₁₂-dependent enzymes?"Vitamin B₁₂ enzymes contain <strong>cobalt (Co)</strong> coordinated in a <strong>corrin ring</strong>.<br>
They form <strong>Co–CH₃</strong> bonds and are involved in <strong>methyltransfer reactions</strong> and <strong>branched-chain amino acid degradation</strong>, particularly in bacteria.<br><img src=""Screen Shot 2025-05-01 at 1.20.05 PM.png"" width=""853"">"
What is the reaction and function of superoxide dismutase (SOD)?"<div>SOD catalyzes the conversion of <strong>2 O₂⁻ + 2 H⁺ → O₂ + H₂O₂</strong> to protect cells from reactive oxygen species.<br>
Different forms exist:</div>
<ul>
<li>
<div><strong>Cu-Zn SOD</strong> in human cytosol</div>
</li>
<li>
<div><strong>Mn SOD</strong> in mitochondria</div>
</li>
<li>
<div><strong>Fe and Ni SOD</strong> in bacteria<br>
It exhibits extremely high catalytic efficiency (<strong>Kcat/Km = 7 × 10⁹ M⁻¹s⁻¹</strong>).</div>
</li></ul><div><img src=""paste-f26bbaee6840bbd1931f477bc06a3759671f7a36.jpg"" width=""678""><br></div>"
What are hydrogenases and what reactions do they catalyze?"<div>Hydrogenases catalyze redox reactions involving <strong>H₂</strong>:</div>
<ol>
<li>
<div><strong>H₂ oxidation</strong>: H₂ + Aₒₓ → 2H⁺ + Aᵣₑd</div>
</li>
<li>
<div><strong>H₂ production via reduction</strong>: 2H⁺ + Dᵣₑd → H₂ + Dₒₓ<br>
These reactions are coupled to <strong>electron acceptors or donors</strong> like <strong>ferredoxins or cytochromes</strong>.</div></li></ol>"
What are the three major types of hydrogenases?"<ul><li><div><strong>NiFe</strong> hydrogenases</div>
</li><li>
<div><strong>FeFe</strong> hydrogenases</div>
</li><li>
<div><strong>Fe-only</strong> hydrogenases<br>
These enzymes are often associated with <strong>Fe-S clusters</strong> for electron transfer and contain <strong>CO and CN ligands</strong> bound to Fe.</div></li><li><div><img src=""paste-3200a9ea5a9b97e088ab05c9cd499ea5a0ee007e.jpg""><br></div></li></ul>
"
What are key features of NiFe hydrogenases?"<ul><li><div>One small subunit with <strong>3 FeS clusters</strong> and a large subunit</div>
</li>
<li>
<div>Sometimes <strong>Ni is replaced by selenocysteine</strong></div>
</li>
<li>
<div>Usually active in <strong>H₂ oxidation</strong></div>
</li>
<li>
<div><strong>Inactivated by O₂</strong>, except in strains like <em>Ralstonia eutropha</em></div></li></ul><div><img src=""paste-e696308998e8b48cc3b11dc7bb28288aab67e5e9.jpg"" width=""912""><i><br></i></div>"
What are the three different families of FeFe hydrogenases?"<ul><li><div><strong>Cytoplasmic monomeric</strong> in strict anaerobes</div>
</li><li>
<div><strong>Periplasmic</strong> hydrogen oxidation (<em>Desulfovibrio</em>)</div>
</li><li>
<div><strong>Soluble monomeric</strong> in <em>Scenedesmus</em> chloroplasts for hydrogen production<br>
FeFe hydrogenases are often more <strong>efficient</strong> and used in <strong>photosynthetic organisms</strong>.</div></li></ul>
"
What is Fe-only hydrogenase and where is it found?"Fe-only hydrogenase (e.g., <strong>5,10-methenyltetrahydromethanopterin hydrogenase</strong>) is found in <strong>methanogenic archaea</strong> and catalyzes the <strong>reduction/oxidation</strong> of <strong>methylenetetrahydromethanopterin</strong>, contributing to <strong>H₂ metabolism</strong> in anaerobic environments.<br><img src=""paste-07a8454d6dd7006c341d078f94887d1bcd90fc9b.jpg""><br>"
What is the primary function of nitrogenase enzymes?Nitrogenase enzymes catalyze the reduction of atmospheric nitrogen (N₂) to ammonia (NH₃), a process called nitrogen fixation.
What is the overall reaction catalyzed by nitrogenase?N₂ + 16 MgATP + 8 e⁻ + 8 H⁺ → 2 NH₃ + H₂ + 16 MgADP + 16 Pᵢ
Why is nitrogen fixation energy-intensive?The N≡N triple bond has a high activation energy (ΔH° = –45.2 kJ/mol; Eₐ ≈ 420 kJ/mol), requiring 8 e⁻ and 8 H⁺ and hydrolysis of 16 ATP molecules for reduction.
What are the two major protein components of the nitrogenase complex?"<ol><li><strong>Fe protein (dinitrogenase reductase):</strong> Transfers electrons using ATP.</li><li><strong>MoFe protein (dinitrogenase):</strong> Contains metal clusters where N₂ reduction occurs<img src=""paste-08463ba1067f45e50ca7992c15bd22f04fc5a4e9.jpg""></li></ol>"
What metal clusters are involved in nitrogenase function?"<ul><li><div><strong><img alt=""Schematic representation of Mo-dependent nitrogenase and its associated... | Download Scientific Diagram"" src=""https://www.researchgate.net/publication/324932622/figure/fig1/AS:622404313300992@1525404160396/Schematic-representation-of-Mo-dependent-nitrogenase-and-its-associated-metal-containing.png""></strong></div></li><li><div><strong>F</strong><strong>e-S (F) cluster</strong>: Transfers electrons to the P cluster.</div></li>
<li>
<div><strong>P cluster</strong>: Intermediate electron carrier.</div>
</li>
<li>
<div><strong>FeMo (M) cluster</strong>: Active site for N₂ binding and reduction.</div>
</li></ul><div><br></div>"
What is the role of the FeMo (M) cluster in nitrogenase?"The FeMo cluster is the site where nitrogen binds and is reduced to ammonia. It is composed of 7 Fe, 1 Mo, 9 S, 1 C (carbide), and R-homocitrate.<br><ul><li>This nitorgenase reduction : Nitrogenase
requires 8 electrons and 8 protons for reduction in steps called E states.The reaction tales place on the <span style=""font-weight: bold;"">FeMo</span><span style=""font-weight: bold;"">
cluster (M)&nbsp; the iron clusters are
holding places for electrons</span>&nbsp;<br></li></ul><div><br></div>"
Which amino acids are near the FeMo cluster and what is their function?"<img src=""Screen Shot 2025-05-01 at 2.04.32 PM.png""><img src=""Screen Shot 2025-05-01 at 2.03.38 PM.png""><br><br>"
"<div>What role does EPR (Electron Paramagnetic Resonance) play in nitrogenase studies?</div>
<div></div>""<div>EPR detects unpaired electrons during the nitrogenase cycle.</div>
<ul>
<li>
<div>In state E₀, FeMo has a spin of 3/2.</div>
</li>
<li>
<div>States with odd numbers of added electrons (n = 1, 3, 5, 7) show EPR signals.</div>
</li>
<li>
<div>Even-numbered states (n = 0, 2, 4, 6, 8) are diamagnetic and EPR silent.</div>
</li>
<li>
<div>ENDOR (Electron-Nuclear Double Resonance) reveals proton hyperfine splitting and local environment, showing hydrides bound to Fe.</div>
</li></ul>"
"<div>What is special about the E₄ state in measuring nitrogenase activity?</div>
<div></div>""<div>E₄ is halfway through the electron/proton transfer cycle (4 e⁻/H⁺ added).</div>
<ul>
<li>
<div>Contains 2 hydrides bound to Fe: [M–H–H–M].</div>
</li>
<li>
<div>Freeze quenching traps it for study.</div>
</li>
<li>
<div>H₂ loss from E₄ reverts the system to E₂ or back to E₀.</div>
</li>
<li>
<div>Identified via ENDOR spectroscopy, proving Fe—not Mo—binds the hydrides.</div>
</li></ul>"
"<div>What is the significance of N₂ binding at E₄?</div>
<div></div>""<ul><li><div><img alt=""Schematic of the reductive-elimination (re)/oxidative-addition (oa)... | Download Scientific Diagram"" src=""https://www.researchgate.net/publication/328507173/figure/fig2/AS:745534239289344@1554760622264/Schematic-of-the-reductive-elimination-re-oxidative-addition-oa-mechanism-2N2H.png"" width=""1014"">The swap of N₂ for the hydride pair (H₂) at E₄ initiates N₂ reduction.</div>
</li>
<li>
<div>This step uses up 2 of the 4 accumulated reducing equivalents.</div>
</li>
<li>
<div>This mechanism is called <b>reductive elimination</b>, making room for N₂ binding and activation.</div></li></ul>"
"<div>What are the <strong>Distal</strong> and <strong>Alternating</strong> pathways in nitrogenase?</div>
<div></div>""<ul><li><div><strong><img src=""paste-4ef5fd3fec71fc27518c8df22f02c08f06876c00.jpg"">Distal (D)</strong>: N₂ binds to Mo, first NH₃ is released from distal nitrogen, leaving a Mo-nitrido intermediate.</div>
</li>
<li>
<div><strong>Alternating (A)</strong>: Hydrogens are added alternatively to both N atoms of N₂, forming diazene (HN=NH), then hydrazine (H₂N–NH₂), then NH₃.<br>
<strong>ENDOR &amp; isotopic studies support the Alternating (A) pathway.</strong></div>
</li></ul><div><b><br></b></div>"
"<div>How does nitrogenase complete the reduction of N₂ to NH₃?</div>
<div></div>""<ul><li>After E₄, sequential proton/electron additions proceed through E₅ to E₈.</li><li>
<div>NH₃ is released at E₇ and again at E₈.</div>
</li><li>
<div>The Fe-S cluster plays a central role in electron delivery and substrate binding.</div>
</li><li>
<div>The enzyme returns to E₀, ready to restart the cycle.</div></li></ul><div><img src=""paste-8379e94469cb17c7cc607b2ba72598210ef88e8b.jpg""><br></div>
"