The 20 common amino acids

Name	Formula (note 1)	Three- letter code	Single-letter code	Occurrence in proteins (%) (note 2)	Properties
Glycine		Gly	G	7.2	small, flexible, nonpolar
Alanine		Ala	A	7.8	small, hydrophobic, nonpolar
Serine		Ser	S	6.8	small, hydrophilic, hydrogen-bonding
Threonine		Thr	T	5.9	hydrophilic, hydrogen-bonding
Proline		Pro	P	5.2	hydrophobic, rigid
Valine		Val	V	6.6	hydrophobic
Leucine		Leu	L	9.1	large, hydrophobic
Isoleucine		Ile	I	5.3	large, hydrophobic
Methionine		Met	M	2.3	large, hydrophobic, pot. metal binder (Fe, Zn,...)
Cysteine		Cys	C	1.9	hydrophobic, forms disulfide bridges, pot. metal binder (Zn, Fe,...)
Aspartic acid (Aspartate)		Asp	D "Aspardate"	5.3	hydrophilic, acidic, negative charge, pot. metal binder (Ca, Mg,...)
Glutamic acid (Glutamate)		Glu	E "Glutamate"	6.3	large, hydrophilic, acidic, negative charge, pot. metal binder (Ca, Mg,...)
Asparagine		Asn	N "Asparagine"	4.3	hydrophilic, polar, hydrogen bonding
Glutamine		Gln	Q "Que?"	4.2	large, hydrophilic, polar, hydrogen bonding
Arginine		Arg	R "Arginine"	5.1	large, hydrophilic, basic, positive charge
Lysine		Lys	K "basik"	5.9	large, hydrophilic, basic, positive charge
Histidine		His	H	2.3	hydrophilic, intermediate pKa, proton shuttle, pot. metal binder (Fe, Zn,...)
Phenylalanine		Phe	F "Fenyl..."	3.9	large, hydrophobic
Tyrosine		Tyr	Y "Tyrosine"	3.2	large, hydrophobic, hydrogen bonding, slightly acidic
Tryptophan		Trp	W "two rings"	1.4	large, hydrophobic, hydrogen bonding

Notes:

1. The formula images are taken from the LIGAND database in KEGG.
2. Values from R.F. Doolittle (1989), calculated from 1150 protein sequences.