"<b><span style=""font-weight: 400;"">In 1952, Alfred Hershey and Martha Chase conducted a series of experiments to prove that ...</span></b>""<b><span style=""font-weight: 400;"">DNA was the genetic material, not proteins</span></b>"
"<b><span style=""font-weight: 400;"">In 1952, ... conducted a series of experiments to prove that DNA was the genetic material</span></b>"Alfred Hershey and Martha Chase
"<b><div><span style=""font-weight: 400;"">... used a method of X-ray diffraction to investigate the structure of DNA –– Photo 51</span></div></b>"Rosalind Franklin and Maurice Wilkins
"<b><div><span style=""font-weight: 400;"">Rosalind Franklin and Maurice Wilkins used a method of X-ray diffraction to ...</span></div></b>"investigate the structure of DNA –– Photo 51
In 1962, ... were awarded the Nobel prize for their contributions to DNA structure identification<b><br></b>Watson, Crick and Wilkins (but not Franklin)&nbsp;
Photo 51 demonstrated that ...the DNA helix is both tightly packed and regular in structure
"<b><span style=""font-weight: 400;"">When Watson &amp; Crick were developing their DNA model, they discovered that ...</span></b>""<b><span style=""font-weight: 400;"">an A–T bond was the same length as a G–C bond</span></b>"
"<b><span style=""font-weight: 400;"">Adenine and thymine paired via ... hydrogen bonds</span></b>"two
Guanine and cytosine paired via ... hydrogen bondsthree
"<b><span style=""font-weight: 400;"">Chargaff demonstrated that DNA is composed of ...</span></b>""<b><span style=""font-weight: 400;"">an equal number of purines (A + G) and pyrimidines (C + T)&nbsp;</span></b>"
purinesadenine, guanine
pyrmidinescytosine, thymine (uracil)
Two mechanisms for DNA replication suggested by DNA structure<ol><li>replication occurs via complementary base pairing</li><li>replication is bidirectional due to the antiparallel nature of the strands</li></ol>
Compare the structure of RNA and DNA<ul><li>ribose pentose sugar (RNA) vs deoxyribose pentose sugar (DNA)</li><li>uracil (RNA) vs thymine (DNA)</li><li>single-stranded (RNA) vs double-stranded helix structure (DNA)</li><li>relatively short polymer (RNA) vs relatively long polymer (DNA)</li></ul>
Describe the genetic code in terms of codons composed of triplets of basesThe genetic code is composed of the four nucleotide bases of DNA (adenine, cytosine, guanine, thymine) in various ways to spell out three-letter codons.&nbsp;<br><ul><li>A triplet of bases forms a codon</li><li>Each codon codes for a particular amino acid</li><li>In translation, amino acids link to form proteins</li><li>DNA and RNA regulate protein synthesis</li></ul>
Discuss the relationship between one gene and one polypeptideOne gene codes for one polypeptide, or a chain of amino acids, which in turn form proteins with other polypeptide chains. Genetic information is stored in DNA by way of nucleotide bases (ATCG), which are organised in&nbsp;<b>codons</b>&nbsp;(triplets of bases). The sequence of codons controls the sequence of amino acids in a polypeptide chain, resulting in the synthesis of a particular protein.&nbsp;
Identify the purpose of non-coding regions of DNANon-coding regions generally control gene expression; the vast majority of the human genome consists of non-coding DNA.
intronsnon-coding sequences within genes
Transcription is carried out in a ... direction"5' to 3'"
Briefly describe the process of transcription<ul><li>Transcription is initiated with the binding of the RNA polymerase to the promoter site</li><li>RNA polymerase uncoils the DNA and separates the two strands</li><li>One of the strands is used as the template strand for transcription, upon which the RNA polymerase uses free nucleoside triphosphates to build the mRNA</li><li>As the nucleoside triphosphates bond to their complementary base pairs, they lose 2 phosphate groups and release energy</li><li>RNA polymerase moves along the DNA and continues producing the mRNA until it reaches the terminator</li><li>The RNA polymerase is released from the DNA and the mRNA separates from the template DNA strand</li><li>DNA winds back into its original double helix structure</li></ul>
The DNA nucleotide structure is composed of...A deoxyribose pentose sugar, a base (adenine, thymine, guanine, cytosine), and a phosphate group
4 bases of DNAadenine, thymine, cytosine, guanine
Outline how DNA nucleotides are linked together by covalent bonds into a single strandNucleotides within a single strand are connected by covalent bonds formed between the sugar of one nucleotide and the phosphate group of another nucleotide
Explain how a DNA double helix is formed using complementary base pairing and hydrogen bondsDNA is made up of two nucleotide strands, which are connected by covalent bonds within each strand (sugar and phosphate); the two strands themselves are connected by hydrogen bonds, which are found between the bases of the two strands. As a result of complementary base pairing, adenine forms hydrogen bonds with thymine, whereas guanine forms hydrogen bonds with cytosine
Molecular structure of DNA"<div style=""text-align: center;""><img alt=""DNA | Definition, Discovery, Function, Bases, Facts, &amp; Structure | Britannica"" src=""DNA-structure-cytosine-thymine-adenine-guanine-phosphate.jpg"" width=""1127""></div>"
Describe the structure of DNA"<ul><li>carbon atoms in deoxyribose are numbered: nitrogenouse bases attached to 1', phosphate group attached to 5'</li><li>nucleotides are joined by a covalent phosphodiester bond between the phosphate and the deoxyribose sugar</li><li>nitrogenous bases interact via hydrogen bonding (complementary base pairing)</li><li>in order for the bases to associate, one strand must run anti-parallel to the other––antiparallel strand runs 3'-5'</li><li>double-stranded DNA forms a double helix with 10 nucleotides per turn</li></ul>"
CBP: adeninethymine
CBP: cytosineguanine
CBT: thymineadenine
CBT: guaninecytosine
nucleosome structure"1 molecule of DNA wrapped around a core of 8 histone proteins (an octamer)<br><ul><li>the negatively charged DNA associates with the positively charged amino acids on the surface of the histone proteins</li><li>the octamer is attached to a H1 protein</li></ul><div style=""text-align: center; ""><img alt=""Difference Between Histones and Nucleosomes | Compare the Difference Between Similar Terms"" src=""Difference-Between-Histones-and-Nucleosomes-fig-2.png"" width=""259""><br></div>"
Nucleosomes help to ...supercoil chromosomes and regulate transcription
Eukaryotic RNA needs the ... to form mature mRNAremoval of introns
Gene expression is regulated by ...proteins that bind to specific base sequences in DNA
Describe the effect of changes in DNA methylation patterns"DNA methylation - process by which methyl groups (CH3) are added to the DNA molecule, preventing the attachment of transcription factors to the gene's promoter region --&gt; thus, methylation can control the expression of genes (epigenetics) and silence a gene through reinforcing DNA coiling"
Describe how the environment of a cell and of an organism has an impact on gene expressionchanges in the external/internal environment can result in changes to gene expression patterns; chemical signals within the cell can trigger changes in levels of regulatory proteins or transcription factors in response to stimuli, alowing gene expression to change in response to alterations in intracellular and extracellular conditions
examples of gene expression being impacted by the environment of a cell or organism<ul><li>hydrangea flowers changing colours depending on the pH of the soil: acidic = blue; alkaline = pink</li><li>humans produce different amount of melanin (skin pigment) depending on light exposure</li><li>certain species of fish, reptile, amphibians can change their gender in response to social cues (e.g. mate availability)</li></ul>
Describe how each tRNA molecule is recognised by a tRNA-activating enzyme that binds a specific amino acid to the tRNA, using ATP for energy."<b><div><span style=""font-weight: 400;"">Each tRNA molecule binds with a specific amino acid in the cytoplasm in a reaction catalysed by a tRNA-activating enzyme</span></div><ul><li><div><span style=""font-weight: 400;"">Each amino acid is recognised by a specific enzyme (the enzyme may recognise multiple tRNA molecules due to degeneracy)</span></div></li></ul><div><span style=""font-weight: 400;"">The binding of an amino acid to the tRNA acceptor stem occurs as a result of a two-step process:</span></div><ul><li><div><span style=""font-weight: 400;"">The enzyme binds ATP to the amino acid to form an amino acid–AMP complex linked by a high energy bond (PP released)</span></div></li><li><div><span style=""font-weight: 400;"">The amino acid is then coupled to tRNA and the AMP is released – the tRNA molecule is now “charged” and ready for use</span></div></li></ul><div><span style=""font-weight: 400;"">The function of the ATP (phosphorylation) is to create a high energy bond that is transferred to the tRNA molecule</span></div><ul><li><div><span style=""font-weight: 400;"">This stored energy will provide the majority of the energy required for peptide bond formation during translation</span></div></li></ul><div style=""text-align: center; ""><img src=""SSZCSErGMiSIIBnjQRkhZPLFV8OsJuXQRAzfe3kpyqepa4SHPL57AmjYcnFWDNWX9_M9wEBdebSMhb779CNAzjtfoT2KtBw80Xl_1_xa00ksx0Z5WLZ.png""></div></b><br>"
"<span style=""text-decoration-line: underline;"">Outline</span> the structure of ribosomes, including protein and RNA composition, large and small subunits, three tRNA binding sites, and mRNA binding sites.&nbsp;""<b><ul><li><div><span style=""font-weight: 400;"">Ribosomes are made of protein (for stability) and ribosomal RNA (for catalytic activity)</span></div></li><li><div><span style=""font-weight: 400;"">They consist of a large and small subunit:</span></div></li><ul><li><div><span style=""font-weight: 400;"">The small subunit contains an mRNA binding site</span></div></li><li><div><span style=""font-weight: 400;"">The large subunit contains three tRNA binding sites – an aminoacyl (A) site, a peptidyl (P) site and an exit (E) site</span></div></li></ul><li><div><span style=""font-weight: 400;"">Ribosomes can be found either freely floating in the cytosol or bound to the rough ER (in eukaryotes)</span></div></li><li><div><span style=""font-weight: 400;"">Ribosomes differ in size in prokaryotes and eukaryotes (prokaryotes = 70S ; eukaryotes = 80S)</span></div></li></ul></b>"
"<span style=""text-decoration-line: underline;"">State</span> that translation consists of..."initiation, elongation, translocation, termination
Initiation (translation)"<b><div><span style=""font-weight: 400;"">The first stage of translation involves the assembly of the three components that carry out the process (mRNA, tRNA, ribosome)</span></div><ul><li><div><span style=""font-weight: 400;"">The small ribosomal subunit binds to the 5’-end of the mRNA and moves along it until it reaches the start codon (AUG)</span></div></li><li><div><span style=""font-weight: 400;"">Next, the appropriate tRNA molecule bind to the codon via its anticodon (according to complementary base pairing)</span></div></li><li><div><span style=""font-weight: 400;"">Finally, the large ribosomal subunit aligns itself to the tRNA molecule at the P site and forms a complex with the small subunit</span></div></li></ul><div style=""text-align: center; ""><img alt=""translation initiation"" src=""QUPgBZiRW3F5KXsKrTSXbQbYhP35YEP7iPpM5X8ZhJ9yERP-j9J6mnXbKyDmabhnvJblkxiGgB_nUgAUz9XMgLjhrrlNnBke2l3vkttRQSz4g5qDmux.jpg""></div></b>"
Elongation (translation)"<b><ul><li><div><span style=""font-weight: 400;"">A second tRNA molecule pairs with the next codon in the ribosomal A site</span></div></li><li><div><span style=""font-weight: 400;"">The amino acid in the P site is covalently attached via a peptide bond (condensation reaction) to the amino acid in the A site</span></div></li><li><div><span style=""font-weight: 400;"">The tRNA in the P site is now deacylated (no amino acid), while the tRNA in the A site carries the peptide chain</span></div></li></ul></b><div style=""text-align: center;""><img alt=""translation elongation"" src=""RoilptOBkJpj8ITHeMbFIfn5wsP02rRakASpqA6I_UzVfxAfF_o5bMzm78vW6EyYujxbaZ_5YoS8jUBLfuolKqVN8643YBLx7kTaiYcvB7eSPyEERG3.jpg"" style=""font-weight: bold;""></div>"
Translocation (translation)"<ul style=""font-weight: bold;""><li><div><span style=""font-weight: 400;"">The ribosome moves along the mRNA strand by one codon position (in a 5’ → 3’ direction)</span></div></li><li><div><span style=""font-weight: 400;"">The deacylated tRNA moves into the E site and is released, while the tRNA carrying the peptide chain moves to the P site</span></div></li><li><div><span style=""font-weight: 400;"">Another tRNA molecules attaches to the next codon in the now unoccupied A site and the process is repeated</span></div></li></ul><div style=""text-align: center; ""><b><img alt=""translation elongation"" src=""RoilptOBkJpj8ITHeMbFIfn5wsP02rRakASpqA6I_UzVfxAfF_o5bMzm78vW6EyYujxbaZ_5YoS8jUBLfuolKqVN8643YBLx7kTaiYcvB7eSPyEERG3.jpg""></b><br></div>"
Termination (translation)"<b><div><span style=""font-weight: 400;"">The final stage of translation involves the disassembly of the components and the release of a polypeptide chain</span></div><ul><li><div><span style=""font-weight: 400;"">Elongation and translocation continue in a repeating cycle until the ribosome reaches a stop codon&nbsp;</span></div></li><li><div><span style=""font-weight: 400;"">These codons do not recruit a tRNA molecule, but instead recruit a release factor that signals for translation to stop</span></div></li><li><div><span style=""font-weight: 400;"">The polypeptide is released and the ribosome disassembles back into its two independent subunits</span></div></li></ul><div>&nbsp;</div><div style=""text-align: center; ""><img alt=""translation termination"" src=""XwsKDTUnoDIhbqFgusGPtvFCbMo-45sYB6uomS9FyAYCGtORPAqHJIE1crIp9kIZHU7cjeTKbW1PgYOs1z7DtJG1UXzlam0TL8XdRTnrbqS1jxN2jtc.jpg""></div></b>"
Translation occurs in a ... direction"5' to 3'"
"<div><span style=""text-decoration-line: underline;"">Explain</span> the process of translation, including ribosomes, polysomes, start codons, and stop codons</div>""<b><ol><li><div><span style=""font-weight: 400;"">The tRNA containing the matching anticodon to the start codon binds to P site of the small subunit of the </span>ribosome</div></li><li><div><span style=""font-weight: 400;"">The small subunit binds to the 5' end of the mRNA and moves along in a 5'→3' direction until it reaches the </span>start codon</div></li><li><div><span style=""font-weight: 400;"">The large subunit then binds to the smaller one</span></div></li><li><div><span style=""font-weight: 400;"">The next tRNA with the matching anticodon to the next codon on the mRNA binds to the A site</span></div></li><li><div><span style=""font-weight: 400;"">The amino acids on the two tRNA molecules form a peptide bond</span></div></li><li><div><span style=""font-weight: 400;"">The larger subunit moves forward over the smaller one&nbsp;</span></div></li><li><div><span style=""font-weight: 400;"">The smaller subunit rejoins the larger one, this moves the ribosome 3 nucleotides along the mRNA and moves the first tRNA to the E site to be released</span></div></li><li><div><span style=""font-weight: 400;"">The second tRNA is now at the P site so that another tRNA with the matching anticodon to the codon on the mRNA can bind to the A site</span></div></li><li><div><span style=""font-weight: 400;"">As this process continues, the polypeptide is elongated</span></div></li><li><div><span style=""font-weight: 400;"">Once the ribosome reaches the </span>stop codon<span style=""font-weight: 400;""> on the mRNA translation ends and the polypeptide is released</span></div></li></ol><span style=""font-weight: 400;"">Many ribosomes can translate a single mRNA at the same time, these groups of ribosomes are called </span>polysomes<br></b><br><div style=""text-align: center;""><img alt=""Role And Structure Of Ribosomes - Translation - MCAT Content"" src=""tRNA-and-Ribosome-Translational-complex-2.jpg"" width=""553""></div>"
Free ribosomes synthesis proteins for use...primarily within the cell, and that bound ribosomes synthesis proteins primarily for secretion or for lysosomes
Explain the significance of complementary base pairing in the conservation of the base sequence of DNA."<b><ul><li><div><span style=""font-weight: 400;"">Complementary base pairing allows for the conservation of the base sequence of DNA, since adenine always pairs up with thymine and guanine always pairs up with cytosine.</span></div></li><li><div><span style=""font-weight: 400;"">As DNA replication is semi-conservative (one old strand and one new strand), this complementary base pairing allows the replicated daughter DNA to be identical to its parent as they have the same base sequence.&nbsp;</span></div></li><li><div><span style=""font-weight: 400;"">The new strands formed are complementary to their template strands but thus identical to the other template.&nbsp;</span></div></li></ul></b>"
DNA replication is...semi-conservative
Explain the process of DNA replication"<b><ol><li><div><span style=""font-weight: 400;"">Coiling strand is relieved by gyrase</span></div></li><li><div><span style=""font-weight: 400;"">DNA double helix is unwound by helicase</span></div></li><li><div><span style=""font-weight: 400;"">By breaking the hydrogen bonds between the bases, the two strands are separated</span></div></li><li><div><span style=""font-weight: 400;"">Single-stranded binding proteins keep the DNA apart</span></div></li><li><div><span style=""font-weight: 400;"">RNA primase adds RNA primer</span></div></li><li><div><span style=""font-weight: 400;"">DNA polymerase III adds free nucleoside triphosphates to the 3’ end of the RNA primer through complementary base pairing</span></div></li><li><div><span style=""font-weight: 400;"">Replication of the lagging strand is discontinuous</span></div></li><ul><li><div><span style=""font-weight: 400;"">DNA polymerase I removes RNA primer and replaces it with free nucleotides</span></div></li><li><div><span style=""font-weight: 400;"">Ligase forms phosphodiester bonds between Okazaki fragments</span></div></li><li><div><span style=""font-weight: 400;"">Replication of the leading strand is continuous</span></div></li></ul><li><div><span style=""font-weight: 400;"">DNA replication is semiconservative</span></div></li></ol></b>"
&nbsp;DNA replication is initiated at...many points in eukaryotic chromosomes
Outline the research of Meselson and Stahl and how this led to the understanding of DNA replication"<b><div><span style=""font-weight: 400;"">Prior to the Meselson-Stahl experiment, three hypotheses had been proposed for the method of replication of DNA:</span></div><ul><li><div><span style=""font-weight: 400; font-style: italic;"">Conservative Model – An entirely new molecule is synthesised from a DNA template (which remains unaltered)</span></div></li><li><div><span style=""font-weight: 400;"">Semi-Conservative Model – Each new molecule consists of one newly synthesised strand and one template strand</span></div></li><li><div><span style=""font-weight: 400;"">Dispersive Model – New molecules are made of segments of new and old DNA</span></div></li></ul><br><div><span style=""font-weight: 400;"">Meselson and Stahl were able to experimentally test the validity of these three models using radioactive isotopes of nitrogen</span></div><ul><li><div><span style=""font-weight: 400;"">Nitrogen is a key component of DNA and can exist as a heavier 15N or a lighter 14N&nbsp;</span></div></li></ul><div><span style=""font-weight: 400;"">DNA molecules were prepared using the heavier 15N and then induced to replicate in the presence of the lighter 14N</span></div><ul><li><div><span style=""font-weight: 400;"">DNA samples were then separated via centrifugation to determine the composition of DNA in the replicated molecules</span></div></li></ul><div><span style=""font-weight: 400;"">The results after two divisions supported the semi-conservative model of DNA replication</span></div><ul><li><div><span style=""font-weight: 400;"">After one division, DNA molecules were found to contain a mix of 15N and 14N, disproving the conservative model</span></div></li><li><div><span style=""font-weight: 400;"">After two divisions, some molecules of DNA were found to consist solely of 14N, disproving the dispersive model</span></div></li></ul></b>"