Biochemistry 20 Common Amino Acids

Generally just know that amine group pKa = 9 and carboxyl group pKa = 2

Leucine*

• Nonpolar

• Leu, L

• α-COOH pKa: 2.4

• α-NH3+ pKa: 9.6

• * Creates a bend in R-chain

Alanine

• Nonpolar

• Ala, A

• α-COOH pKa: 9.7

• α-NH3+ pKa: 2.4

Valine

• Nonpolar

• Val, V

• α-COOH pKa: 2.3

• α-NH3+ pKa: 9.6

Proline

• Nonpolar

• Pro, P

• α-COOH pKa: 2.1

• α-NH3+ pKa: 10.6

Methionine*

• Nonpolar

• Met, M

• α-COOH pKa: 2.3

• α-NH3+ pKa: 9.2

• * Oxidized at the sulfur

Tryptophan

• Nonpolar

• Trp, W

• α-COOH pKa: 2.4

• α-NH3+ pKa: 9.4

Phenylalanine

• Nonpolar

• Phe, F

• α-COOH pKa: 1.8

• α-NH3+ pKa: 9.1

Isoleucine

• Nonpolar

• Ile, I

• α-COOH pKa: 2.4

• α-NH3+ pKa: 9.7

Glycine

• Polar, uncharged

• Gly, G

• α-COOH pKa: 2.3

• α-NH3+ pKa: 9.6

Serine*

• Polar, uncharged

• Ser, S

• α-COOH pKa: 2.2

• α-NH3+ pKa: 9.2

• R-Group pKa: ~13

• * Weak acid and can give up H+

Asparagine

• Polar, uncharged

• Asn, N

• α-COOH pKa: 2.0

• α-NH3+ pKa: 8.8

Glutamine

• Polar, uncharged

• Gln, Q

• α-COOH pKa: 2.2

• α-NH3+ pKa: 9.1

Threonine

• Polar, uncharged

• Thr, T

• α-COOH pKa: 2.6

• α-NH3+ pKa: 10.4

• R-Group pKa: ~13

Cysteine*

• Polar, uncharged

• Cys, C

• α-COOH pKa: 1.7

• α-NH3+ pKa: 10.8

• R-Group pKa: 8.3

• * Disulfide bridge

Tyrosine

• Polar, uncharged

• Tyr, Y

• α-COOH pKa: 2.2

• α-NH3+ pKa: 9.1

• R-Group pKa: 10.1

Aspartic Acid

• Acidic

• Asp, D

• α-COOH pKa: 2.1

• α-NH3+ pKa: 9.8

• R-Group pKa: 3.9

Glutamic Acid

• Acidic

• Glu, E

• α-COOH pKa: 2.2

• α-NH3+ pKa: 9.7

• R-Group pKa: 4.3

Lysine*

• Basic

• Lys, K

• α-COOH pKa: 2.2

• α-NH3+ pKa: 9.0

• R-Group pKa: 10.5

• * Most common

Arginine*

• Basic

• Arg, R

• α-COOH pKa: 2.2

• α-NH3+ pKa: 9.0

• R-Group pKa: 12.5

• * Most common

Histidine*

• Basic

• His, H

• α-COOH pKa: 1.8

• α-NH3+ pKa: 9.2

• * R-Group pKa: 6.0