Ac ad em y Vi si on Intensive Lecture 2. 习题训练 Exercise 3. 课堂总结 Review Vi si on Ac ad em y Vi si on Ac ad em y Vi si on Vi si on Biochemistry 1. 知识精讲 Ac ad em y Ac ad em y 目 录 Contents 1 Biochemistry Ac ad em y Elements, Atoms and Compounds Basics of Biochemistry - • Ø Elementary Organic Chemistry • Compounds: a substance consisting of two or more different elements combinedin a fixed ratio Enzymes Ac ad em y Large Biological Molecules Vi si on Ø Elements, Compounds and Water Element: a substance that cannot be broken down to other substances by chemical reactions I an means Atom: the smallest unit of matter that retains the properties of an element • Vi si on Part 1 Elements and Compounds Sodium Chlorine Sodium chloride 1 Elements and Compounds Chemical Bonds: Covalent Bonds and Ionic Bonds • Essential elements: an organism needs to live a healthy Ac ad em y Ø Nonpolar covalent bonds: electrons are shared equally as the two atoms have the same life and reproduce. For example, 25 elements for humans Trace elements: essential elements but in only minute Vi si on • electronegativity Ø Polar covalent bonds: the electrons of the bond are not shared equally • quantities. For example, iron (Fe) for all forms of life, and Ionic bonds: the attraction between the cation (+) and anion (-) Vi si on iodine (I) for vertebrates to produce thyroxin • There are elements toxic to organisms, for example, arsenic 2 Weak Chemical Interactions Cl– Chloride ion (an anion) Properties of Water for Life The polarity of water molecules results in hydrogen bonding. There are also weak chemical interactions between and within molecules. Hydrogen bonds: the attraction between a hydrogen and an electronegative atom nearby • Van der Waals interaction: attraction by charge differences between molecules or atoms in Ac ad em y • close proximity Na+ Sodium ion (a cation) Vi si on Elements and Compounds Vi si on 1 Water (H2O) Polar Ac ad em y Vi si on Ac ad em y Oxygen (O2) Nonpolar Cl Na • The water molecule is a polar molecule: The opposite ends have opposite charges • Polarity allows water molecules to form hydrogen bonds with each other Ac ad em y and 17 for plants Covalent bonds: the sharing of a pair of valence electrons by two atoms Vi si on • 1 Ac ad em y The Elements of Life Ac ad em y Elements and Compounds Vi si on 1 Hydrogen bonds Forming of Hydrogen bonds 2 Ac ad em y 2 Properties of water contribute to Earth’s fitness for life. Properties of Water for Life Cohesive behavior of water • • Ability to moderate temperature • Expansion upon freezing • Versatility as a solvent Cohesion: a phenomenon that hydrogen bonds hold water molecules together • Adhesion: the attraction between different substances, e.g. water and plant cell walls • Ac ad em y Cohesive behavior Vi si on • Ac ad em y Four of water’s properties that facilitate an environment for life are: Surface tension: a phenomenon at the surface of a liquid caused by intermolecular forces • Vi si on Properties of Water for Life Vi si on 2 Cohesion helps the transport of water against gravity Vi si on Properties of Water for Life 2 Insulation of Bodies of Water by Floating Ice Specific heat: the amount of heat that be absorbed or lost for 1 g of that substance to change • dense Ac ad em y its temperature by 1ºC • Evaporative cooling: a process that remains surface cools while a liquid evaporates • Water has a high specific heat because of the hydrogen bonding, which minimizes temperature fluctuations to within limits that permit life • Ice floats in liquid water because hydrogen bonds in ice are more “ordered,” making ice less • When a deep body of water cools, the floating ice insulates the liquid water below, preventing Vi si on • Properties of Water for Life Ac ad em y Moderation of Temperature Vi si on 2 Ac ad em y Vi si on Ac ad em y in plants, and surface tension is related to cohesion. it from freezing and allowing life to exist under the frozen surface Evaporative cooling of water helps stabilize temperatures in organisms and bodies of water 3 The Solvent of Life Ac ad em y Vi si on Properties of Water for Life Water is a versatile solvent due to its polarity, which allows it to form hydrogen bonds easily • pH: Acids and Bases The pH scale measures the H+ concentration of a solution. • The pH of a solution is defined by the negative logarithm of H+ concentration: pH = –log [H+] Large polar molecules such as proteins can dissolve in water if they have ionic and polar regions • In any aqueous solution at 25°C, the product of H+ and OH– is constant: [H+][OH–] = 10–14 • A substance that has an/no affinity for water is hydrophilic/hydrophobic • pH values less than 7 in acidic solutions, greater than 7 in basic solutions • Most biochemical reactions occur in an aqueous solution which facilitates the collisions of • Buffers: substances that minimize changes in concentrations of H+ and OH– in a solution Vi si on Ac ad em y Vi si on Ac ad em y Vi si on molecules Vi si on Ac ad em y • 3 Ac ad em y 2 Quizzes Quizzes Clothes washing detergent must be able to remove grease and oil stains from clothing while 10-6 molar? (Hint: You don’t need a calculator!) ( also dissolving and washing away in the rinse water. Which of the following is the correct C. 5.7 D. 6 E. 6.4 structure of the detergent molecules and the correct reason for it? ( ) A. Detergent molecules are polar and are therefore able to dissolve both grease and water. Vi si on Ac ad em y B. 2-6 Vi si on A. 2 ) Ac ad em y (2010 USABO) What is the pH of a solution where the concentration of hydrogen ions is 2 × B. Detergent molecules are nonpolar and are therefore able to dissolve in both grease and water. C. One end of a detergent molecule is nonpolar in order to dissolve oily stains, while the other end is polar to dissolve in the rinse water. D. One end of a detergent molecule is polar in order to dissolve oily stains, while the other end is nonpolar to dissolve in the rinse water. 4 Ac ad em y Vi si on Biochemistry 1 Isomers Isomers: same molecular formula, different structures and properties. Basics of Biochemistry Structural isomers have different covalent arrangements of their atoms Ø Elements, Compounds and Water • cis-trans isomers have the same covalent arrangements but differ in spatial arrangements Ø Elementary Organic Chemistry • Enantiomers are isomers that are mirror images of each other Vi si on Part 1 Ac ad em y Ac ad em y • Large Biological Molecules Vi si on Functional Groups 2 Functional Groups Functional groups are the components of organic molecules that are most commonly involved Ac ad em y in chemical reactions • The number and arrangement of functional groups give each molecule its unique properties • Seven functional groups, such as hydroxyl, carbonyl and carboxyl group, are most important in the chemistry of life Vi si on • Ac ad em y Functional groups are important in the processes of life. Vi si on 2 Ac ad em y Vi si on Ac ad em y Vi si on Enzymes 5 Ac ad em y Vi si on Macromolecules Built from Monomers Polymers are built from monomers. A polymer is a long molecule consisting of many similar building blocks called monomers • A condensation or dehydration reaction occurs when two monomers bond together through The Condensation Reaction and Hydrolysis Three classes of life’s organic molecules are both macromolecules and polymers: Ac ad em y Hydrolysis disassembles polymers to monomers • Vi si on • Ø Proteins Ø Nucleic acids Ac ad em y Condensation Vi si on the loss of a water molecule Ø Carbohydrates Macromolecules Built from Monomers Ac ad em y • 3 Vi si on Ac ad em y Vi si on 1 Biochemistry Ac ad em y Basics of Biochemistry • Monosaccharides: the simplest carbohydrates such as glucose and galactose Large Biological Molecules • Disaccharide: two monosaccharides joins by a dehydration reaction, such as sucrose formed Ø Lipids Ø Proteins Ø Nucleic acids by glucose and fructose, lactose formed by glucose and galactose • Vi si on Ø Carbohydrates Ac ad em y Part 1 Monosaccharides and Disaccharide Carbohydrates serve as fuel and building material. Vi si on 3 Polysaccharides: polymers composed of many sugar building blocks Enzymes 6 Ac ad em y Monosaccharides and Disaccharide Monosaccharides are usually multiples of CH2O. Monosaccharides and Disaccharide Disaccharide consists of two monosaccharides. Monosaccharides are classified by: Ac ad em y • 1 Vi si on 1 Ø The location of the carbonyl group (as aldose or ketose) • A disaccharide is formed when a dehydration reaction joins two monosaccharides • This covalent bond is called a glycosidic linkage Ø The number of carbons in the carbon skeleton raw material for building molecules Many sugars form rings in aqueous solutions Glucose Ac ad em y Ac ad em y Vi si on 3 Polysaccharides, the polymers of sugars, have storage and structural roles. The difference is based on two ring forms for glucose: alpha (α) and beta (β) structure and function of a polysaccharide • Starch is helical and cellulose is straight because of the different linkage • Many herbivores have symbiotic relationships with some microbes that have enzymes to digest Ac ad em y • Storage polysaccharides: starch (a storage polysaccharide in plants), glycogen (a storage polysaccharide in animals) • Both starch and cellulose are polymers of glucose. Sugar monomers and the positions of glycosidic linkages determines the Structural polysaccharides: cellulose (a major component of the cell wall of Vi si on • Structure of Starch and Cellulose Ac ad em y Polysaccharides • Sucrose Dehydration reaction in the synthesis of sucrose Vi si on 2 Fructose 1–2 glycosidic linkage cellulose Vi si on • Vi si on Ac ad em y Monosaccharides serve as a major fuel for cells and as Vi si on • plant), chitin (found in the exoskeleton of arthropods and cell walls of many fungi) Chitin monomer 7 Ac ad em y The Benedict‘s Test Ø Amylopectin (branched, 支链), with α-1,6 linkage at the branch points • Reducing sugar: all monosaccharides and most disaccharides (except sucrose) • Benedict‘s reagent: an aqueous solution of CuSO4, Na2CO3 and sodium citrate, and blue CuSO4 are reduced to red Cu2O in Benedict’s test • Sucrose (non-reducing) is hydrolyzed with dilute HCl first, neutralized with NaHCO3 and then can be tested positive with Benedict’s reagent • A blue-black colour indicates the presence of starch when treated with Vi si on 直链), with α-1,4 linkage Ac ad em y Two kinds of starch: Ø Amylose (unbranched, • Tests for Carbohydrates Vi si on • 4 Ac ad em y Both starch and cellulose are polymers of glucose. Vi si on Structure of Starch and Cellulose Glycogen is like amylopectin drops of iodine/KI solution but more extensively Ac ad em y branched Vi si on Ac ad em y Vi si on Quizzes Quizzes ( ) only by 1,4 glycosidic bonds? ( ) B. glycogen C. glycerol D. glucagon B. Amylose C. Cellulose Vi si on A. glycine A. Amylopectin Ac ad em y (2020 BBO, 1) In which of the following polymers would you find alpha glucose joined Ac ad em y Which of the following is stored in the human liver to be used later as a source of energy? Vi si on 3 D. Glycogen 8 Ac ad em y Vi si on Biochemistry 1 Lipids Lipids do not form polymers and have little or no affinity for water. Basics of Biochemistry Ac ad em y • covalent bonds Large Biological Molecules • The most biologically important lipids are fats, phospholipids, and steroids Vi si on Ac ad em y Ø Carbohydrates Part 1 Lipids are hydrophobic because they consist mostly of hydrocarbons, which form nonpolar Ø Lipids Vi si on Ø Proteins Ø Nucleic acids Ac ad em y Enzymes Vi si on Fats 2 Fats Saturated fatty acids and unsaturated fatty acids Glycerol is a three-carbon alcohol with a hydroxyl group attached to each carbon • A fatty acid consists of a carboxyl group attached to a long carbon skeleton • Three fatty acids are joined to glycerol, creating a triacylglycerol or triglycerides • Saturated fats: fats made from saturated fatty acids, solid at room temperature • The major function of fats is energy storage • Unsaturated fats (also called oils): fats made from unsaturated fatty acids, liquid at room Glycerol Saturated fatty acids have no double bonds, and unsaturated fatty acids have one or more double bonds temperature • Vi si on Ac ad em y • Ester bond • Ac ad em y Fats are constructed from glycerol and fatty acids. Vi si on 2 Cholesterol, a steroid Phospholipid symbol Ac ad em y Vi si on Fat molecule (triacylglycerol) Plant fats and fish fats are usually unsaturated Fat molecule (triacylglycerol) 9 Ac ad em y Vi si on In phospholipid, 2 fatty acids and 1 phosphate group are attached to glycerol • Vi si on Phospholipids are the major component of nearly all cell membranes, forming a bilayer Some hormones are made from steroids, such as sex hormones Cholesterol Ac ad em y Vi si on arrangement Cholesterol is a component in animal cell membranes, and high level of cholesterol in blood may contribute to cardiovascular disease • When phospholipids are added to water, they self-assemble into a bilayer, with the hydrophobic tails pointing toward the interior • Steroids are characterized by a carbon skeleton consisting of four fused rings. The two fatty acid tails are hydrophobic, but the phosphate group and its attachments form a hydrophilic head • Steroids Ac ad em y • 4 Ac ad em y Phospholipids Phospholipid Vi si on Ac ad em y Vi si on Quizzes Biochemistry Ac ad em y Phospholipids and triglycerides both ________. ( ) B) have three fatty acids Large Biological Molecules C) have a glycerol backbone D) have a phosphate Part 1 Ø Carbohydrates Ø Lipids Vi si on Basics of Biochemistry Ac ad em y A) contain serine or some other organic compound Vi si on 3 Ø Proteins Ø Nucleic acids Enzymes 10 Ac ad em y 2 Proteins have many structures, resulting in a wide range of functions. Polypeptides are polymers built from the same set of 20 amino acids. • Protein functions include structural support, storage, transport, cellular communications, Ac ad em y • Polypeptides movement, and defense against foreign substances • properties due to differing side chains, called R groups • Enzymes are a type of protein that acts as a catalyst to speed up chemical reactions, and they Two amino acids are joined together through a dehydration reaction, forming a peptide bond. Repeating the process over and over creates a polypeptide chain Vi si on can perform their functions repeatedly Amino acids are organic molecules with carboxyl and amino groups, differ in their • Ac ad em y Functions of Proteins Vi si on 1 Each polypeptide has a unique linear sequence of amino acids, and a protein consists of one or Ac ad em y Vi si on more polypeptides Vi si on Polypeptides 2 Amino Acids Ø Nonpolar amino acids: have nonpolar R groups and are Ø Nonpolar amino acids: have nonpolar R groups and are that are charged (ionized) at cellular pH and are hydrophilic Ø Polar amino acids: have polar R groups and are hydrophilic Ø Electrically charged amino acids: have functional groups that are charged (ionized) at cellular pH and are Vi si on Ø Electrically charged amino acids: have functional groups hydrophobic Ac ad em y hydrophobic Ø Polar amino acids: have polar R groups and are hydrophilic Polypeptides Ac ad em y Amino Acids Vi si on 2 Peptide bond Carboxyl group Ac ad em y Vi si on Amino group hydrophilic 11 A protein consists of one or more polypeptides twisted, folded, and coiled into a unique shape • Four levels of protein structure: the primary, the secondary, the tertiary and the quaternary • The primary structure of a protein is its unique sequence of amino acids, which determines Secondary Structure • Secondary structure consists of coils and folds in the polypeptide chain resulted from hydrogen bonds between repeating constituents of the polypeptide backbone • Typical secondary structures are a coil called an α helix and a folded structure called a β pleated sheet Ac ad em y Vi si on Vi si on the three-dimensional structure of the protein The Three-Dimensional Structure of Proteins Ac ad em y • 3 Ac ad em y A protein’s structure determines its function. Ac ad em y Protein Structure and Function Vi si on 3 • Quaternary structure results when two or more polypeptide chains form one macromolecule various side chains (R groups), which include hydrogen • Collagen is a fibrous protein consisting of three polypeptides coiled like a rope • Hemoglobin is a globular protein consisting of two α and two β subunits, both consist Waals interactions Strong covalent bonds called disulfide bridges may reinforce the protein’s structure primarily of α-helical secondary structure Vi si on Tertiary structure is determined by interactions among bonds, ionic bonds, hydrophobic interactions, and van der • The Three-Dimensional Structure of Proteins Quaternary Structure Ac ad em y • 3 Ac ad em y Tertiary Structure Vi si on The Three-Dimensional Structure of Proteins Vi si on 3 β pleated sheet Ac ad em y Vi si on α helix 12 Ac ad em y Physical and chemical conditions can affect protein structure • Alterations in pH, salt concentration, temperature, or other environmental factors can cause a protein to unravel Fat Emulsion Test and Biuret Test • This loss of a protein’s native structure is called denaturation, and a denatured protein is Biuret reagent is initially blue, but forms a violet colour when added to a solution containing proteins Ac ad em y Vi si on biologically inactive Dissolve the substance with absolute ethanol, then decant the mixture into water, a cloudy white suspension is formed with the presence of lipids (fat emulsion test) • Vi si on • Tests for Lipids and Proteins Ac ad em y • 5 Ac ad em y Various factors affect protein structure. Vi si on Factors that Affect Protein Structure Vi si on Ac ad em y Vi si on Quizzes Quizzes following EXCEPT a: ( ) A. Iron B. Change in the secondary structure of the protein C. Loss of catalytic activity of the protein D. Loss of a negatively charged side chain C. Nitrogen D. Phosphorus Vi si on A. Change in the quaternary structure of the protein B. Oxygen Ac ad em y (2019 BBO, 9) Which of the following elements is NOT present in haemoglobin? ( ) Ac ad em y (2011 USABO) Replacement of a lysine with a glycine in a protein could result in all of the Vi si on 4 E. Hydrogen E. Loss of the protein’s ability to interact with other proteins 13 Ac ad em y Vi si on Biochemistry 1 The Roles of Nucleic Acids Nucleic acids store and transmit hereditary information. Basics of Biochemistry Ac ad em y • acid (DNA) and ribonucleic acid (RNA) Large Biological Molecules • Ø Carbohydrates Gene expression: DNA directs synthesis of messenger Ø Lipids synthesis in ribosomes Vi si on Ø Proteins Ac ad em y RNA (mRNA) and, through mRNA, controls protein Vi si on Part 1 There are two types of nucleic acids: deoxyribonucleic Ø Nucleic acids Vi si on The Structure of Nucleic Acids 2 Nucleotide Monomers • Each nucleotide consists of a nitrogenous base, a pentose sugar, and a • phosphate group Ø Pyrimidines (Cytosine, Thymine, and Uracil) have a single • The portion of a nucleotide without the phosphate group is called a nucleoside • In DNA, the sugar is deoxyribose, and in RNA the sugar is ribose Nitrogenous base Sugar (pentose) Deoxyribose (in DNA) Ribose (in RNA) There are two families of nitrogenous bases: six-membered ring Ø Purines (Adenine and Guanine) have a six-membered ring fused to a five-membered ring • NDA strand Vi si on Nucleic acids are polynucleotides made of monomers called nucleotides Ac ad em y • Phosphate group The Structure of Nucleic Acids Ac ad em y Nucleic acids are polymers call polynucleotides. Vi si on 2 Ac ad em y Vi si on Ac ad em y Enzymes Base pairing: A=T and C≡G in DNA, A=U instead in RNA Nitrogenous bases Nucleoside 14 The Structure of Nucleic Acids Energy Currency: ATP • Adjacent nucleotides are joined by phosphodiester linkage Ac ad em y • 3 that form between the –OH group on the 3’ carbon of one nitrogenous base adenine, and a chain of three phosphate groups. • nucleotide and the phosphate on the 5’ carbon on the next These links create a backbone of sugar-phosphate units with The terminal phosphate bond breaks, releasing a molecule of inorganic phosphate (HOPO32-, Pi) and a ADP (adenosine diphosphate) • ATP can be regenerated by addition of a phosphate group to ADP Ac ad em y Vi si on nitrogenous bases as appendages Vi si on • ATP (adenosine triphosphate) is a nucleotide triphosphate consisting of the sugar ribose, the Ac ad em y Nucleotide Polymers Ac ad em y The Structure of Nucleic Acids Vi si on 3 Vi si on The DNA Double Helix 5 • Chromatin: a complex of DNA and protein, found in the nucleus of eukaryotic cells spiraling around an imaginary axis, forming a • Histones: proteins that are responsible for the first level of DNA packing in chromatin • Nucleosome: “beads” resembled from unfolded chromatin (10 nm in diameter); the “string” The two backbones run in opposite 5’ → 3’ directions from each other, which is referred to as antiparallel • The nitrogenous bases in DNA pair up and form between beads is linker DNA Vi si on A DNA molecule has two polynucleotides double helix • Chromatin is composed of DNA and histones. Ac ad em y • Components of Chromosomes Ac ad em y DNA is a double helix that stores genetic information. Vi si on 4 Ac ad em y Vi si on Phosphodiester linkage in the covalent backbone of DNA and RNA hydrogen bonds (A — T, G—C), thus the two strands are complementary 15 Heterochromatin: tightly packed form of DNA or condensed DNA • Euchromatin: loosely packed form of chromatin • Dense packing of the heterochromatin makes it difficult for the cell to express genetic There are two chromosomes of each of 23 types in human somatic cells. • Karyotype (核型): an ordered display of the pairs of chromosomes from a cell • Homologous chromosomes: the two chromosomes of a pair with the same length, centromere position, and staining pattern • X and Y are called sex chromosomes, the others are called autosomes Vi si on Ac ad em y Vi si on Ac ad em y Vi si on Vi si on information coded in these regions Sets of Chromosomes in Human Cells Ac ad em y • 7 Ac ad em y There are different packed stations of chromatins. Ac ad em y Euchromatin and Heterochromatin Vi si on 6 Quizzes Quizzes G/C pairs form with 3 hydrogen bonds, whilst A/T pairs form with 2 hydrogen bonds. A. There are always equal amounts of guanine and cytosine nucleotides Which of the following helices will denature at the highest temperature? ( ) D. Phosphodiester bonds link adjacent nucleotides E. Hydrogen bonds are the major forces that maintain a double helix structure A. Short strand with a high proportion of A/T base pairs. Vi si on C. Uracil pairs with adenine Vi si on B. Purine bases pair with pyrimidine bases Ac ad em y (2019 BBO, 7) Heat causes the two strands of DNA helices to separate (melt / denature). one ? ( ) Ac ad em y (2015 BBO, 11) The following statements about the structure of DNA are all true except which B. Long strand with a high proportion of A/T base pairs. C. Short strand with a high proportion of G/C base pairs. D. Long strand with a high proportion of G/C base pairs. 16 Ac ad em y Vi si on 1 Enzymes as Catalysts Enzymes speed up metabolic reactions by lowering energy barriers. Biochemistry Ac ad em y • reaction without being consumed by the reaction 1. Elements and Compounds • 2. Water and Life Enzymes catalyze reactions by lowering the barrier of free energy of activation (or activation Vi si on energy, EA), the initial energy needed to start a chemical reaction • 3. Elementary Organic Chemistry Ac ad em y Part 1 An enzyme is a macromolecule that acts as a catalyst, a chemical agent that speeds up a Enzymes do not affect the change in free energy (∆G), only hasten reactions that would occur eventually Vi si on 4. Large Biological Molecules Vi si on Enzymes as Catalysts 1 The substrate binds to the active site of the enzyme. • The enzyme binds to its substrate with active site, forming an enzyme- • Enzyme models: Ø The lock and key model Ø The induced fit (诱导契合) model • The active site can lower an EA barrier by: Ø Orienting substrates correctly Ø Straining substrate bonds Ø Providing a favorable microenvironment Ø Covalently bonding to the substrate • Vi si on Substrate: the reactant that an enzyme acts on Ac ad em y • substrate complex Enzymes as Catalysts Ac ad em y An enzyme can recognize its specific substrate. Vi si on 1 Ac ad em y Vi si on Ac ad em y 5. Enzymes The enzyme reaches the saturated state, the concentration of substrate will be high enough that all enzyme molecules will have their active sites engaged 17 Competitive and Noncompetitive inhibitors 2 Effects of Local Conditions Temperature, pH and Cofactors • Enzyme inhibitors: chemicals that selectively inhibit the action of specific enzymes Ac ad em y • Ac ad em y Effects of Local Conditions Vi si on 2 Ø Competitive inhibitors bind to the active site of an enzyme, competing with the substrate Temperature and pH: each enzyme has an optimal temperature and pH to function, for example, 70℃ for thermophilic bacteria and low pH for pepsin Ø Noncompetitive inhibitors bind to another part of an enzyme, causing the enzyme to change shape and • making the active site less effective, such as toxins, poisons, pesticides and antibiotics Cofactors: nonprotein enzyme helpers, often for chemical processes like electron transfers Vi si on Ac ad em y Ø Examples of inorganic cofactor: Zn2+, Fe3+, Cu2+ Vi si on Effects of Local Conditions 3 • Michaelis–Menten constant, Km, is the substrate concentration at which an enzyme works at half • Ac ad em y Turnover rate: the number of substrate molecules converted by one enzyme molecule per second • Allosteric regulation (变构调节) occurs when a regulatory molecule binds to a protein at one site and affects the protein’s function at another site • Each enzyme has active and inactive forms Ø The binding of an activator stabilizes the active form of the enzyme Vmax gives information about the maximum rate of reaction that is possible and Km measures the affinity of the enzyme for the substrate Ac ad em y Allosteric regulation may either inhibit or stimulate an enzyme’s activity. • its maximum rate Allosteric Regulation and Feedback Inhibition Vi si on Michaelis–Menten Constant Vi si on 2 Ac ad em y Vi si on Ac ad em y Vi si on Ø Examples of organic cofactor (coenzyme): most vitamins Ø The binding of an inhibitor stabilizes the inactive form of the enzyme • Cooperativity (协同效应): binding by a substrate to one active site stabilizes favorable conformational changes at all other subunits, thus amplify enzyme activity Ø The binding of oxygen to hemoglobin (though not an enzyme) 18 Ac ad em y Vi si on Allosteric Regulation and Feedback Inhibition 4 Allosteric Regulation and Feedback Inhibition Feedback Inhibition Ac ad em y • Feedback inhibition: a metabolic pathway is halted by the inhibitory binding of its end product to an enzyme that acts early in the pathway Feedback inhibition prevents a cell from wasting chemical Ac ad em y Vi si on • Vi si on resources by synthesizing more product than is needed Ac ad em y Cooperativity: another type of allosteric activation Feedback inhibition in isoleucine synthesis Allosteric activators and inhibitors Vi si on Ac ad em y Vi si on Quizzes Quizzes (2011 USABO) In the example, assume that D is an allosteric inhibitor of the enzyme E2. D following pathway, where E represents different enzymes, and A, B, C, D and F represent would ( ) A. Compete with B for binding to the E2 active site Vi si on Ac ad em y substrates and products of the pathway. Feedback inhibition of this pathway may involve ( ) Ac ad em y (2011 USABO) Many metabolic pathways involve multi-step reactions. Consider the Vi si on 3 A. The product of the final reaction, F, interacting with and inhibiting E1 B. Compete with F for binding with E2 B. F interacting with and inhibiting product B C. Bind directly to the substrate B and prevent it from entering the E2 active site C. Product B interacting with and inhibiting E4 D. Product C interacting with and inhibiting E4 E. E3 interacting with and inhibiting E2 D. Bind E2 at a site different from the active site but change the shape of the active site so B can no longer bind E. Bind E2 at the active site, change its shape and prevent B from binding the active site 19 Ac ad em y Vi si on All the following are carbohydrates except ( ) A. starch. B. glycogen. Exercise C. chitin. D. glycerol. Vi si on 习题训练 Exercise 3 习题训练 Exercise (2006 USABO) The molecular weight of fumarate is 160.0. How many grams of fumarate using Benedict's solution. The same volume of glucose and Benedict's solution was are there in 200 mL of a 0.1M fumarate solution? ( ) B. Sample 2: yellow C. Sample 3: green D. Sample 4: brick-red Place the samples in decreasing order of concentration. A. 0.32 grams B. 3.20 grams Vi si on A. Sample 1: orange Ac ad em y used in each case. After 5 minutes the colour of the precipitate was noted: Ac ad em y (2020 BBO, 2) Four different concentrations of glucose solution were each tested Vi si on 2 Ac ad em y Vi si on Ac ad em y E. cellulose. Ac ad em y Vi si on 习题训练 习题训练 Exercise Vi si on Ac ad em y Part 2 1 C. 8.00 grams D. 80.00 grams E. 3.20 kg 20 Ac ad em y Vi si on 习题训练 Exercise 5 习题训练 Exercise Maltotriose is a trisaccharide composed of three glucose molecules linked through α-1,4 membrane?( ) glycosidic linkages formed via dehydration synthesis. What would the formula be for B. C18H10O15 C. C. C18H32O16 D. C3H6O3 Ac ad em y E. B. ) Ac ad em y A. C18H36O18 Vi si on A. maltotriose? ( Vi si on Ac ad em y (2014 USABO) Which of the following is NOT a component of the cell wall or cell D. Vi si on Ac ad em y Vi si on 课堂总结 Review Ac ad em y 课堂总结 Review Vi si on Part 3 Ac ad em y 1 Vi si on 4 21 Ac ad em y Ac ad em y Vi si on Vi si on Vi si on Ac ad em y Vi si on Ac ad em y Vi si on Ac ad em y Vi si on Ac ad em y 谢谢聆听,下次课再见~ Exercise 1D 2DABC 3~5BDC 22 Vi si on Ac ad em y