Amino Acids: Complete List of the 20 Standard Proteinogenic Amino Acids

The 20 Canonical Amino Acids

Name	3-Letter	1-Letter	Side Chain Property
Alanine	Ala	A	Nonpolar, aliphatic
Arginine	Arg	R	Basic, positively charged
Asparagine	Asn	N	Polar, uncharged
Aspartic acid	Asp	D	Acidic, negatively charged
Cysteine	Cys	C	Polar, thiol (forms disulfide bonds)
Glutamic acid	Glu	E	Acidic, negatively charged
Glutamine	Gln	Q	Polar, uncharged
Glycine	Gly	G	Nonpolar, smallest
Histidine	His	H	Basic, partially charged at pH 7
Isoleucine	Ile	I	Nonpolar, branched
Leucine	Leu	L	Nonpolar, branched
Lysine	Lys	K	Basic, positively charged
Methionine	Met	M	Nonpolar, sulfur-containing
Phenylalanine	Phe	F	Aromatic, nonpolar
Proline	Pro	P	Nonpolar, cyclic (imino acid)
Serine	Ser	S	Polar, uncharged (hydroxyl)
Threonine	Thr	T	Polar, uncharged (hydroxyl)
Tryptophan	Trp	W	Aromatic, nonpolar
Tyrosine	Tyr	Y	Aromatic, polar (phenolic OH)
Valine	Val	V	Nonpolar, branched

Additional Notes

• Selenocysteine (Sec, U) and pyrrolysine (Pyl, O) are the 21st/22nd genetically encoded amino acids (rare, specific organisms/contexts).
• Post-translational modifications create many derivatives (phosphoserine, hydroxyproline, etc.).
• Nine are essential (cannot be synthesized): His, Ile, Leu, Lys, Met, Phe, Thr, Trp, Val.