The 20 common natural amino acids:

Alanine         Ala   A
Arginine        Arg   R
Asparagine      Asn   N
Aspartic acid   Asp   D
Cysteine        Cys   C
Glutamine       Gln   Q
Glutamic acid   Glu   E
Glycine         Gly   G
Histidine       His   H
Isoleucine      Ile   I
Leucine         Leu   L
Lysine          Lys   K
Methionine      Met   M
Phenylalanine   Phe   F
Proline         Pro   P
Serine          Ser   S
Threonine       Thr   T
Tryptophan      Trp   W
Tyrosine        Tyr   Y
Valine          Val   V