AminoAcidsProteinsandEnzymesHartnell氨基酸的蛋白质与酶.pptx

1Functions of Proteins Proteins perform many different functions in the body.2Amino AcidsAmino acids are the building blocks of proteins.contain a carboxylic acid group and an amino group on the alpha()carbon.are ionized in solution.each contain a different side group(R).R side chain R +H2NC COOH H3NC COO H H Zwitterion(ionized form)3Types of Amino AcidsAmino acids are classified asnonpolar(hydrophobic)with hydrocarbon side chains.polar(hydrophilic)with polar or ionic side chains.acidic(hydrophilic)with acidic side chains.basic(hydrophilic)with NH2 side chains.Nonpolar PolarAcidicBasic Copyright 2009 by Pearson Education,Inc.4Nonpolar Amino AcidsAn amino acid is nonpolar when the R group is H,alkyl,or aromatic.Copyright 2009 by Pearson Education,Inc.5Polar Amino AcidsAn amino acid is polar when the R group is an alcohol,thiol,or amide.Copyright 2009 by Pearson Education,Inc.6Acidic and Basic Amino AcidsAn amino acid is acidic when the R group is a carboxylic acid.basic when the R group is an amine.7Learning Check Identify each as(1)polar or(2)nonpolar.+A.H3NCH2COO Glycine CH3|CHOH +B.H3NCHCOO Threonine8Solution Identify each as(1)polar or(2)nonpolar.+A.H3NCH2COO Glycine (2)nonpolar CH3|CHOH +B.H3NCHCOO Threonine (1)polar9Fischer Projections of Amino AcidsAmino acids are chiral except glycine.have Fischer projections that are stereoisomers.that are L are the only amino acids used in proteins.L-Alanine D-Alanine L-Cysteine D-CysteineCH2SHH2NHCOOHCH2SH HNH2 COOHCH3HNH2COOHCH3H2NHCOOH10A zwitterion has charged NH3+and COO groups.forms when both the NH2 and the COOH groups in an amino acid ionize in water.has equal+and charges at the isoelectric point(pI).O O +NH2CH2COH H3NCH2CO Glycine Zwitterion of glycineZwitterions11In solutions more basic than the pI,the NH3+in the amino acid donates a proton.+OHH3NCH2COO H2NCH2COO ZwitterionNegative ion at pI pH pI Charge:0Charge:1-Amino Acids as Acids12In solution more acidic than the pI,the COO in the amino acid accepts a proton.+H+H3NCH2COOH3NCH2COOH Zwitterion Positive ionat pI pH pI Charge:0Charge:1+Amino Acids as Bases13pH and ionization H+OH+H3NCH2COOH H3NCH2COO H2NCH2COO Positive ion Zwitterion Negative ionlow pH pI high pH14Separation of Amino AcidsWhen an electric current is used to separate a mixture ofamino acidsthe positively charged amino acids move towards the negative electrode.the negatively charged amino acids move toward the positive electrode.an amino acid at its pI does not migrate.the amino acids are identified as separate bands on the filter paper or thin layer plate.15Separation of Amino AcidsWith an electric current,a mixture of lysine,aspartate,and valine are separated.Copyright 2009 by Pearson Education,Inc.16 CH3 CH3 +|H3NCHCOOH H2NCHCOO(1)(2)Which structure represents A.alanine at a pH above its pI?B.alanine at a pH below its pI?Learning Check17 CH3 CH3 +|H3NCHCOOH H2NCHCOO(1)(2)Which structure represents A.alanine at a pH above its pI?(2)B.alanine at a pH below its pI?(1)Solution1816.4 Formation of PeptidesChapter 16 Amino Acids,Proteins,and Enzymes Copyright 2009 by Pearson Education,Inc.19The Peptide BondA peptide bondis an amide bond.forms between the carboxyl group of one amino acid and the amino group of the next amino acid.O CH3 O +|+|H3NCH2CO +H3NCHCO O H CH3 O +|H3NCH2CNCHCO peptide bond20Formation of a Dipeptide Copyright 2009 by Pearson Education,Inc.21Naming DipeptidesA dipeptide is named from the free amine(NH3+)using a-yl ending for the name.names the last amino acid with the free carboxyl group(COO)by its amino acid name.22Write the three-letter abbreviations and names of the tripeptides that could form from two glycine and one alanine.Learning Check 23Write the names and three-letter abbreviations of the tripeptides that could form from two glycine and one alanine.Glycylglycylalanine Gly-Gly-Ala Glycylalanylglycine Gly-Ala-GlyAlanylglycylglycine Ala-Gly-Gly Solution 24Learning Check Write the three-letter abbreviation and name for thefollowing tetrapeptide.CH3 CH3 S CHCH3 SH CH2 CH3 O H CH O H CH2 O H CH2 O +H3NCHCNCHCNCHCNCHCO25Solution Ala-Leu-Cys-MetAlanylleucylcysteinylmethionine CH3 CH3 S CHCH3 SH CH2 CH3 O H CH O H CH2 O H CH2 O +H3NCHCNCHCNCHCNCHCOAlaLeuCysMet2616.5 Levels of Protein StructureChapter 16 Amino Acids,Proteins,and Enzymes Copyright 2009 by Pearson Education,Inc.27Primary Structure of ProteinsThe primary structure of a protein isthe particular sequence of amino acids.the backbone of a peptide chain or protein.AlaLeuCysMet28Primary StructuresThe nonapeptides oxytocin and vasopressin have similar primary structures.Only the amino acids at positions 3 and 8 differ.Copyright 2009 by Pearson Education,Inc.29Primary Structure of InsulinInsulinwas the first protein to have its primary structure determined.has a primary structure of two polypeptide chains linked by disulfide bonds.has a chain A with 21 amino acids and a chain B with 30 amino acids.30Secondary StructureAlpha HelixThe secondary structure of analpha helix isa three-dimensional spatial arrangement of amino acids in a polypeptide chain.held by H bonds between the H of N-H group and the O of C=O of the fourth amino acid down the chain.a corkscrew shape that looks like a coiled“telephone cord.”Copyright 2009 by Pearson Education,Inc.31Secondary StructureBeta-Pleated SheetThe secondary structure of a beta-pleated sheetconsists of polypeptide chains arranged side by side.has hydrogen bonds between chains.has R groups above and below the sheet.is typical of fibrous proteins,such as silk.32Secondary StructureTriple Helix The secondary structure of a triple helix isthree polypeptide chains woven together.typical of collagen,connective tissue,skin,tendons,and cartilage.33Indicate the type of protein structure.1)primary 2)alpha helix3)beta-pleated sheet 4)triple helixA.polypeptide chains held side by side by H bondsB.sequence of amino acids in a polypeptide chainC.corkscrew shape with H bonds between amino acidsD.three peptide chains woven like a ropeLearning Check34Indicate the type of protein structure.1)primary 2)alpha helix3)beta-pleated sheet 4)triple helixA.3 polypeptide chains held side by side by H bondsB.1 sequence of amino acids in a polypeptide chainC.2 corkscrew shape with H bonds between amino acidsD.4 three peptide chains woven like a ropeSolution35must be obtained from the diet.are 10 amino acids not synthesized by the body.are in meat and dairy products.are missing(one or more)in grains and vegetables.Essential Amino AcidsEssential amino acids 36Tertiary StructureThe tertiary structureof a protein is an overall 3-dimensional shape.is determined by attractions and repulsions between the side chains of the amino acids in a peptide chain.37Crosslinks in Tertiary StructuresCrosslinks in tertiary structures involve attractions and repulsions between the side chains of the amino acids in the polypeptide chain.38Select the type of tertiary interaction.1)disulfide2)ionic3)H bonds4)hydrophobicA.leucine and valineB.two cysteinesC.aspartic acid and lysineD.serine and threonineLearning check39Select the type of tertiary interaction.1)disulfide2)ionic3)H bonds4)hydrophobicA.4 leucine and valineB.1 two cysteinesC.2 aspartic acid and lysineD.3 serine and threonineSolution40Globular ProteinsGlobular proteins have compact,spherical shapes.carry out synthesis,transport,and metabolism in the cells.such as myoglobin store and transport oxygen in muscle.Copyright 2009 by Pearson Education,Inc.Myoglobin41Quaternary StructureThe quaternary structure is the combination of two or more protein units.of hemoglobin consists of four polypeptide chains as subunits.is stabilized by the same interactions found in tertiary structures.Copyright 2009 by Pearson Education,Inc.42Fibrous ProteinsFibrous proteinsconsist of long,fiber-like shapes.such as alpha keratins make up hair,wool,skin,and nails.such as feathers contain beta keratins with large amounts of beta-pleated sheet structures.43Summary of Protein Structure44Summary of Protein Structure45Identify the level of protein structure.1)primary2)secondary3)tertiary 4)quaternaryA.beta-pleated sheetB.order of amino acids in a proteinC.a protein with two or more peptide chainsD.the shape of a globular proteinE.disulfide bonds between R groupsLearning Check46Identify the level of protein structure.1)primary2)secondary3)tertiary 4)quaternaryA.2 beta-pleated sheetB.1 order of amino acids in a proteinC.4 a protein with two or more peptide chainsD.3 the shape of a globular proteinE.3 disulfide bonds between R groupsSolution47Denaturation involves the disruption of bonds in the secondary,tertiary,and quaternary protein structures.heat and organic compounds that break apart H bonds and disrupt hydrophobic interactions.acids and bases that break H bonds between polar R groups and disrupt ionic bonds.heavy metal ions that react with S-S bonds to form solids.agitation such as whipping that stretches peptide chains until bonds break.Denaturation48Denaturation of protein occurs whenan egg is cooked.the skin is wiped with alcohol.heat is used to cauterize blood vessels.instruments are sterilized in autoclaves.Applications of Denaturation Copyright 2009 by Pearson Education,Inc.49Tannic acid is used to form a scab on a burn.An egg is hard boiled by placing it in boiling water.What is similar about these two events?Learning Check50Acid and heat cause the denaturation of protein.They both break bonds in the secondary and tertiary structures of proteins.Solution51Chapter 16 Amino Acids,Proteins,and Enzymes16.6 Enzymes16.7 Enzyme Action52Enzymes are Biological CatalystsEnzymes are proteins that Catalyze nearly all the chemical reactions taking place in the cells of the body.Increase the rate of reaction by lowering the energy of activation.53The name of an enzymeusually ends in ase.identifies the reacting substance.For example,sucrase catalyzes the reaction of sucrose.describes the function of the enzyme.For example,oxidases catalyze oxidation.could be a common name,particularly for the digestion enzymes,such as pepsin and trypsin.Names of Enzymes54Enzymes are classified by the reaction they catalyze.ClassType of Reactions CatalyzedOxidoreductasesOxidation-reductionTransferasesTransfer groups of atomsHydrolases HydrolysisLyasesAdd atoms/remove atoms to orfrom a double bondIsomerasesRearrange atomsLigasesUse ATP to combine small moleculesClassification of Enzymes55Match the type of reaction with an enzyme.1)aminase2)dehydrogenase3)isomerase4)synthetaseA.Converts a cis-fatty acid to a trans-fatty acid.B.Removes 2 H atoms to form double bond.C.Combines two molecules to make a new compound.D.Adds NH3.Learning Check56Match the type of reaction with an enzyme1)aminase2)dehydrogenase3)isomerase4)synthetaseA.3 Converts a cis-fatty acid to a trans-fatty acid.B.2 Removes 2 H atoms to form double bond.C.4 Combines two molecules to make a new compound.D.1 Adds NH3.Solution57The active site is a region within an enzyme that fits the shape of the reacting molecule called a substrate.contains amino acid R groups that bind the substrate.releases products when the reaction is complete.Active Site58Enzyme-Catalyzed ReactionIn an enzyme-catalyzed reactiona substrate attaches to the active site.an enzyme-substrate(ES)complex forms.reaction occurs and products are released.an enzyme is used over and over.E+S ES E+P59Lock-and-Key Model In the lock-and-key model,theactive site has a rigid shape.enzyme only binds substrates that exactly fit the active site.enzyme is analogous to a lock.substrate is the key that fits that lock.Copyright 2009 by Pearson Education,Inc.60Induced-Fit ModelIn the induced-fit modelenzyme structure is flexible,not rigid.enzyme and substrate adjust the shape of the active site to bind substrate.the range of substrate specificity increases.shape changes improve catalysis during reaction.Copyright 2009 by Pearson Education,Inc.61Example of an Enzyme-Catalyzed Reaction 62Learning Check A.The active site is(1)the enzyme(2)a section of the enzyme(3)the substrateB.In the induced-fit model,the shape of the enzyme when substrate binds(1)stays the same(2)adapts to the shape of the substrate63Solution A.The active site is(2)a section of the enzymeB.In the induced-fit model,the shape of the enzyme when substrate binds(2)adapts to the shape of the substrate64Diagnostic Enzymes Diagnostic enzymesdetermine the amount of damage in tissues.that are elevated may indicate damage or disease in a particular organ.65Diagnostic Enzymes Levels of enzymes CK,LDH,and AST are elevated following a heart attack.are used to determine the severity of the attack.Copyright 2009 by Pearson Education,Inc.66Isoenzymes Isoenzymescatalyze the same reaction in different tissues in the body.can be used to identify the organ or tissue involved in damage or disease.such as lactate dehydrogenase(LDH),which converts lactate to pyruvate,consists of five isoenzymes.such as LDH have one form more prevalent in heart muscle and another form in skeletal muscle and liver.67Isoenzymes Copyright 2009 by Pearson Education,Inc.68Chapter 16 Amino Acids,Proteins,and Enzymes16.8 Factors Affecting Enzyme Activity69Enzymesare most active at an optimum temperature(usually 37 C in humans).show little activity at low temperatures.lose activity at high temperatures as denaturation occurs.Temperature and Enzyme Action70Enzymesare most active at optimum pH.contain R groups of amino acids with proper charges at optimum pH.lose activity in low or high pH as tertiary structure is disrupted.pH and Enzyme Action71Optimum pH ValuesEnzymes inthe body have an optimum pH of about 7.4.certain organs operate at lower and higher optimum pH values.72Substrate ConcentrationAs substrate concentration increases,the rate of reaction increases(at constant enzyme concentration).the enzyme eventually becomes saturated,giving maximum activity.73Sucrase has an optimum temperature of 37 C and an optimum pH of 6.2.Determine the effect of the following on its rate of reaction.1)no change 2)increase 3)decrease A.Increasing the concentration of sucroseB.Changing the pH to 4C.Running the reaction at 70 C Learning Check74Sucrase has an optimum temperature of 37 C and an optimum pH of 6.2.Determine the effect of the following on its rate of reaction.1)no change 2)increase 3)decrease A.2 Increasing the concentration of sucraseB.3 Changing the pH to 4C.3 Running the reaction at 70 C Solution75Inhibitorsare molecules that cause a loss of catalytic activity.prevent substrates from fitting into the active sites.E+SESE+P E+I EI no PEnzyme Inhibition76Competitive InhibitionA competitive inhibitorhas a structure that is similar to that of the petes with the substrate for the active site.has its effect reversed by increasing substrate concentration.77A noncompetitive inhibitorhas a structure that is much different than the substrate.distorts the shape of the enzyme,which alters the shape of the active site.prevents the binding of the substrate.cannot have i