All proteins are polymers of the 20 naturally occuring L-amino acids. They
are listed here along with their abbreviations :
| Alanine | Ala | A |
| Cysteine | Cys | C |
| Aspartic AciD | Asp | D |
| Glutamic Acid | Glu | E |
| Phenylalanine | Phe | F |
| Glycine | Gly | G |
| Histidine | His | H |
| Isoleucine | Ile | I |
| Lysine | Lys | K |
| Leucine | Leu | L |
| Methionine | Met | M |
| AsparagiNe | Asn | N |
| Proline | Pro | P |
| Glutamine | Gln | Q |
| ARginine | Arg | R |
| Serine | Ser | S |
| Threonine | Thr | T |
| Valine | Val | V |
| Tryptophan | Trp | W |
| TYrosine | Tyr | Y |
In addition B may used for Asx (Aspartate or Asparagine) and X for Glx (Glutamate or Glutamine). J, O and U are not used.
It is important to take the time to commit the single letter code to memory, as it is invariably used when comparing and aligning sequences of proteins. Most are easily remembered by their initial letters. Try and invent for yourself memorable mnemonic aids to remember the others. Note that Cysteine and Methionine are the only two sulphur-containing AAs.