A Quick-Reference Guide to the 20 Common Amino Acids

2025-12-03 3

Nonpolar Amino Acids (Hydrophobic Amino Acids)

No.

Name

Three- letter code

One-letter code

Isoelectric Point（PI）

Molecular Weight（Da）

Codons（5’→3’）

Molecular Formula（MF）

Structural formula

1

Alanine

Ala

A

6.01

89.09

GCU, GCC,

GCA, GCG

C₃H₇NO₂

2

Isoleucine

Ile

I

6.02

131.18

AUU, AUC,

AUA

C₆H₁₃NO₂

3

Leucine

Leu

L

5.98

131.18

UUA, UUG,

CUU, CUC,

CUA, CUG

C₆H₁₃NO₂

4

Valine

Val

V

5.97

117.15

GUU, GUC,

GUA, GUG

C₅H₁₁NO₂

5

Methionine

Met

M

5.74

149.21

AUG

C₅H₁₁NO₂S

6

Phenylalanine

Phe

F

5.48

165.19

UUU, UUC

C₉H₁₁NO₂

7

Tryptophan

Trp

W

5.89

204.23

UGG

C₁₁H₁₂N₂O₂

8

Proline

Pro

P

6.3

115.13

CCU, CCC,

CCA, CCG

C₅H₉NO₂

9

Glycine

Gly

G

5.97

75.07

GGU, GGC,

GGA, GGG

C₂H₅NO₂

Polar Amino Acids

No.

Name

Three- letter code

One-letter code

Isoelectric Point（PI）

Molecular Weight（Da）

Codons（5’→3’）

Molecular Formula（MF）

Structural formula

1

Serine

Ser

S

5.68

UCU, UCC,

UCA, UCG,

AGU, AGC

105.09

C₃H₇NO₃

2

Threonine

Thr

T

5.6

ACU, ACC,

ACA,ACG

119.12

C₄H₉NO₃

3

Cysteine

Cys

C

5.07

UGU, UGC

121.2

C₃H₇NO₂S

4

Tyrosine

Tyr

Y

5.66

UAU, UAC

181.19

C₉H₁₁NO₃

5

Asparagine

Asn

N

5.41

AAU, AAC

132.1

C₄H₈N₂O₃

6

Glutamine

Gln

Q

5.65

CAA, CAG

146.15

C₅H₁₀N₂O₃

Basic Amino Acids

No.

Name

Three- letter code

One-letter code

Isoelectric Point（PI）

Molecular Weight（Da）

Codons（5’→3’）

Molecular Formula（MF）

Structural formula

1

Lysine

Lys

K

9.74

AAA, AAG

146.19

C₆H₁₄N₂O₂

2

Arginine

Arg

R

10.76

CGU, CGC,

CGA, CGG,

AGA, AGG

174.2

C₆H₁₄N₄O₂

3

Histidine

His

H

7.59

CAU, CAC

155.15

C₆H₉N₃O₂

Acidic Amino Acids

No.

Name

Three- letter code

One-letter code

Isoelectric Point（PI）

Molecular Weight（Da）

Codons（5’→3’）

Molecular Formula（MF）

Structural formula

1

Aspartic Acid

Asp

D

2.77

GAU, GAC

133.1

C₄H₇NO₄

2

Glutamic Acid

Glu

E

3.22

GAA, GAG

147.13

C₅H₉NO₄