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Chapter 24 slides - Chapter 24 Amino Acids, Peptides, and...

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Chapter 24 Amino Acids, Peptides, and Proteins
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Chapter 24 2 Proteins • Biopolymers of α -amino acids. • Amino acids are joined by peptide bond. • Variety of functions: ¾ structure ¾ enzymes ¾ transport ¾ protection ¾ hormones => Carboxypeptidase animation
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Chapter 24 3 Structure of Proteins =>
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Chapter 24 4 Amino Acids •- N H 2 on the carbon next to -COOH. • Glycine, NH 2 -CH 2 -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. =>
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Chapter 24 5 Stereochemistry of α -Amino Acids =>
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Chapter 24 6 Standard Amino Acids • Twenty standard α -amino acids. • Differ in side-chain characteristics: ¾ -H or alkyl ¾ contains an -OH ¾ contains sulfur ¾ contains a nonbasic nitrogen ¾ has -COOH ¾ has a basic nitrogen =>
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Chapter 24 7 Essential Amino Acids (must be provided in our diet) • Arginine (Arg) • Threonine (Thr) • Lysine (Lys) • Valine (Val) • Phenylalanine (Phe) • Tryptophan (Trp) • Methionine (Met) • Histidine (His) • Leucine (Leu) • Isoleucine (Ile) =>
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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. =>
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Chapter 24 9 Rare Amino Acids • 4-Hydroxyproline, 5-hydroxylysine found in collagen. •D -Glutamic acid in cell walls of bacteria -Serine in earthworms γ -Aminobutyric acid, a neurotransmitter β -Alanine, constituent of the vitamin pantothenic acid. =>
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Chapter 24 10 Zwitterion • Amino acid exists as a dipolar ion. • -COOH loses H + , -NH 2 gains H + . Actual structure depends on pH. =>
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Chapter 24 11 Properties of Amino Acids • High melting points, over 200 ° C • More soluble in water than in ether. • Larger dipole moments than simple acids or simple amines. • Less acidic than most carboxylic acids, less basic than most amines. H 3 NC H R C O O + _ p K a = 10 p K b = 12 =>
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Chapter 24 12 Structure and pH =>
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Chapter 24 13 Isoelectric Point • pH at which amino acids exist as the zwitterion (neutral).
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Chapter 24 slides - Chapter 24 Amino Acids, Peptides, and...

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