AminoAcidsProteinsandEnzymesHartnell氨基酸的蛋白质与酶.pptx
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1、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 H3
2、NC 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 Copyrig
3、ht 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 B
4、asic 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
5、 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 COOHCH3HNH2COOHCH3H2N
6、HCOOH10A 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 amin
7、o 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
8、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 a
9、cids 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 Pears
10、on 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)Solution181
11、6.4 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 +|H3NCH2
12、CNCHCO 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 abbreviatio
13、ns 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-
14、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 +H3NCHCNC
15、HCNCHCNCHCOAlaLeuCysMet2616.5 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.AlaLeuCys
16、Met28Primary 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
17、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 b
18、etween 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 a
19、rranged 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,t
20、endons,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
21、 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 wo
22、ven 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-dim
23、ensional 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.38Selec
24、t 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 asp
25、artic 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 Struc
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