The Foundations of Chemistry

POLYPEPTIDES AND PROTEINS

Two amino acids can react to form an amide bond (see Section 27-19). Compounds formed

by the linking of small numbers of amino acids are called peptides,and the amide bond

linking the amino acid monomers is called the peptide bond.

28-9

TABLE 28-6 The 20 Common Amino Acids Found in Proteins

Nonpolar R Groups

alanine (Ala)
phenylalanine (Phe)

glycine (Gly)

proline (Pro)

isoleucine (Ile)

tryptophan (Trp)
leucine (Leu)

methionine (Met) valine (Val)

Polar, Neutral R Groups

asparagine (Asn) serine (Ser)

glutamine (Gln) threonine (Thr)

Polar, Acidic R Groups Polar, Basic R Groups

aspartic acid (Asp)

arginine (Arg)

glutamic acid (Glu)

cysteine (Cys)

histidine (His)

tyrosine (Tyr) lysine (Lys)

CH 3 CHCOOH

NH 2

HCHCOOH

NH 2

CH 3 CH 2 CHCHCOOH

CH 3

NH 2

(CH 3 ) 2 CHCH 2 CHCOOH

NH 2

CH 3 SCH 2 CH 2 CHCOOH

NH 2

H 2 NCCH 2 CHCOOH

NH 2

O

H 2 NCCH 2 CH 2 CHCOOH

NH 2

O

HOOCCH 2 CHCOOH

NH 2

HOOCCH 2 CH 2 CHCOOH

NH 2

HSCH 2 CHCOOH

NH 2

HO CH 2 CHCOOH

NH 2

CH 2 CHCOOH

NH 2

N COOH

H

CH 2 CHCOOH

NH 2

N

H

(CH 3 ) 2 CHCHCOOH

NH 2

HOCH 2 CHCOOH

NH 2

CH 3 CHCHCOOH

NH 2

OH

H 2 NCNHCH 2 CH 2 CH 2 CHCOOH

NH 2

NH

N CH^2 CHCOOH

N

H NH^2

H 2 NCH 2 CH 2 CH 2 CH 2 CHCOOH

NH 2