Organic Chemistry,6th Edition L.G.Wade,Jr. Chapter 24 Amino Acids. Peptides,and Proteins Jo Blackburn Richland College,Dallas,TX Dallas County Community College District ©2006，Prentice Hall
Chapter 24 Amino Acids, Peptides, and Proteins Jo Blackburn Richland College, Dallas, TX Dallas County Community College District © 2006, Prentice Hall Organic Chemistry, 6th Edition L. G. Wade, Jr
Proteins Biopolymers of a-amino acids. Amino acids are joined by peptide bond. Variety of functions: >structure >enzymes >transport >protection >hormones 二> Chapter 24 2
Chapter 24 2 Proteins • Biopolymers of -amino acids. • Amino acids are joined by peptide bond. • Variety of functions: ➢structure ➢enzymes ➢transport ➢protection ➢hormones =>
Structure of Proteins a carbon atom H.N-CH-C-OH a-amino group R -side chain an a-amino acid H2N-CH-C-OH H2N-CH-C-OH HN-CH- OH HN-CH-C-OHHN-CH-C-OH CH,OH H CH2SH CH(CH3)2 alanine serine glycine cysteine valine several individual amino acids peptide bonds -NH-CH一C-NH- CH-CNHCH- NH-CH- NH- CH- CH3 CHOH H CH,SH CH(CH3) a short section of a protein Copyright2005 Pearson Prentice Hall,Inc. Chapter 24 3
Chapter 24 3 Structure of Proteins =>
Amino Acids .-NH2 on the carbon next to -COOH. Glycine,NH2-CH2-COOH,is simplest. With-R side chain,molecule is chiral. Most natural amino acids are L-amino acids,related to L-(-)-glyceraldehyde. Direction of optical rotation,(+)or () must be determined experimentally. > Chapter 24
Chapter 24 4 Amino Acids • -NH2 on the carbon next to -COOH. • Glycine, NH2 -CH2 -COOH, is simplest. • With -R side chain, molecule is chiral. • Most natural amino acids are L-amino acids, related to L-(-)-glyceraldehyde. • Direction of optical rotation, (+) or (-), must be determined experimentally. =>
Stereochemistry of a-Amino Acids COOH CHO COOH HO C R H H COOH CHO COOH H HO H H2N H CH3 CH2OH R L-alanine L-(-)-glyceraldehyde an L-amino acid (S)-alanine (S)-glyceraldehyde (S)configuration Copyright2005 Pearson Prentice Hall,Inc. => Chapter 24 5
Chapter 24 5 Stereochemistry of -Amino Acids =>
Standard Amino Acids Twenty standard a-amino acids. Differ in side-chain characteristics: >-H or alkyl >contains an -OH >contains sulfur >contains a nonbasic nitrogen >has -COOH >has a basic nitrogen > Chapter 24 6
Chapter 24 6 Standard Amino Acids • Twenty standard -amino acids. • Differ in side-chain characteristics: ➢ -H or alkyl ➢contains an -OH ➢contains sulfur ➢contains a nonbasic nitrogen ➢has -COOH ➢has a basic nitrogen =>
Essential Amino Acids ·Arginine(Arg) ·Tryptophan(Trp) ·Threonine(Thr) ·Methionine(Met) ·Lysine(Lys) 。Histidine(His) ·Valine (Val) ·Leucine(Leu) ·Phenylalanine(Phe)·Isoleucine(le) > Chapter 24 7
Chapter 24 7 Essential Amino Acids • Arginine (Arg) • Threonine (Thr) • Lysine (Lys) • Valine (Val) • Phenylalanine (Phe) • Tryptophan (Trp) • Methionine (Met) • Histidine (His) • Leucine (Leu) • Isoleucine (Ile) =>
Complete Proteins Provide all the essential amino acids. Examples:those in meat,fish,milk,eggs. Plant proteins are generally incomplete. Vegetarians should eat many different kinds of plants,or supplement diet with milk or eggs. => Chapter 24
Chapter 24 8 Complete Proteins • Provide all the essential amino acids. • Examples: those in meat, fish, milk, eggs. • Plant proteins are generally incomplete. • Vegetarians should eat many different kinds of plants, or supplement diet with milk or eggs. =>
Rare Amino Acids 4-Hydroxyproline,5-hydroxylysine found in collagen. D-Glutamic acid in cell walls of bacteria. D-Serine in earthworms. y-Aminobutyric acid,a neurotransmitter. B-Alanine,constituent of the vitamin pantothenic acid. > Chapter 24 0
Chapter 24 9 Rare Amino Acids • 4-Hydroxyproline, 5-hydroxylysine found in collagen. • D-Glutamic acid in cell walls of bacteria. • D-Serine in earthworms. • -Aminobutyric acid, a neurotransmitter. • -Alanine, constituent of the vitamin pantothenic acid. =>
Zwitterion Amino acid exists as a dipolar ion. .-COOH loses H+,-NH2 gains H+. H,N一CH一C-OH HN-CH-C- R R uncharged structure dipolar ion,or zwitterion (minor component) (major component) Copyright2005 Pearson Prentice Hall,Inc. Actual structure depends on pH. Chapter 24 =>10
Chapter 24 10 Zwitterion • Amino acid exists as a dipolar ion. • -COOH loses H+ , -NH2 gains H+ . • Actual structure depends on pH. =>