《有机化学》课程PPT教学课件（Organic Chemistry，5th Edition，L. G. Wade, Jr.，Prentice Hall）Chapter 24 Amino Acids, Peptides, and Proteins

Organic Chemistry,5th Edition L.G.Wade,Jr. Chapter 24 Amino Acids. Peptides,and Proteins Jo Blackburn Richland College,Dallas,TX Dallas County Community College District ©2003，Prentice Hall

Chapter 24 Amino Acids, Peptides, and Proteins Jo Blackburn Richland College, Dallas, TX Dallas County Community College District © 2003, Prentice Hall Organic Chemistry, 5th 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 => 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 一OH a-amino group R -side chain an d-amino acid peptide bonds 3-NH-CH-C-NH-CH一C∠NH一CH-C-NH-CH一C-NH-CH一( CH3 CH2OH H CH>SH CH(CH3)2 a short section of a protein H2N-CH-C-OH H2N-CH-C OHHN一CH一C OHHN一CH- C- OH H2N-CH- OH CH3 CHOH H CH2SH CH(CH3)2 alanine serine glycine cysteine valine individual amino acids 三> 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 H CCH-OH H COOH CHO COOH H2N- -H HO H H2N- H CH3 CH,OH R (S)-alanine L-(-)-glyceraldehyde an L-amino acid (L-alanine) (S)configuration => 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 8

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+. HN-CH-C-OHHN CHc-o R R uncharged structure dipolar ion,or zwitterion (minor component) (major component) 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. =>