IMGT Education

Amino acids

Formula of the 20 common amino acids and structural details of the side chains

Formula of the 20 common amino acids
Structural details of the side chains: formula, 3D model and atoms nomenclature

Formula of the 20 common amino acids

The formula of an amino acid comprises, bound to a carbon (alpha carbon):

a carboxyl group -COOH
an amine group -NH2
an atom of hydrogen -H
a variable radical -R, that is the functional group (in red in the table) of the amino acid.

Chemically speaking, an amino acid is a carboxylic acid which has an amine group attached to it. The general linear formula of an amino acid is R-CH(NH2)-COOH.

The 20 common amino acids are grouped in classes according to their side chains:

Click here for IMGT classes of the 20 common amino acids 'Physicochemical' properties.

Structural formula

Amino acids with uncharged side chains

POLAR SIDE CHAINS		NON POLAR SIDE CHAINS
SERINE		GLYCINE
THREONINE		ALANINE
TYROSINE		CYSTEINE ⁽¹⁾
ASPARAGINE		VALINE
GLUTAMINE		LEUCINE
		ISOLEUCINE
		PROLINE
		METHIONINE
		PHENYLALANINE
		TRYPTOPHAN

Amino acids with charged side chains

Charged side chains are POLAR.

ACIDIC SIDE CHAINS		BASIC SIDE CHAINS
ASPARTIC ACID		LYSINE
GLUTAMIC ACID		ARGININE
		HISTIDINE

⁽¹⁾ Paired cysteines allow disulfide bonds to form in proteins: -CH2-S-S-CH2-

Molecular and linear formulas

Amino acid	Abbreviations		Molecular formula	Linear formula
Alanine	Ala	A	C₃H₇NO₂	CH3-CH(NH2)-COOH
Arginine	Arg	R	C₆H₁₄N₄O₂	HN=C(NH2)-NH-(CH2)3-CH(NH2)-COOH
Asparagine	Asn	N	C₄H₈N₂O₃	H2N-CO-CH2-CH(NH2)-COOH
Aspartic acid	Asp	D	C₄H₇NO₄	HOOC-CH2-CH(NH2)-COOH
Cysteine	Cys	C	C₃H₇NO₂S	HS-CH2-CH(NH2)-COOH
Glutamine	Gln	Q	C₅H₁₀N₂O₃	H2N-CO-(CH2)2-CH(NH2)-COOH
Glutamic acid	Glu	E	C₅H₉NO₄	HOOC-(CH2)2-CH(NH2)-COOH
Glycine	Gly	G	C₂H₅NO₂	NH2-CH2-COOH
Histidine	His	H	C₆H₉N₃O₂	NH-CH=N-CH=C-CH2-CH(NH2)-COOH
Isoleucine	Ile	I	C₆H₁₃NO₂	CH3-CH2-CH(CH3)-CH(NH2)-COOH
Leucine	Leu	L	C₆H₁₃NO₂	(CH3)2-CH-CH2-CH(NH2)-COOH
Lysine	Lys	K	C₆H₁₄N₂O₂	H2N-(CH2)4-CH(NH2)-COOH
Methionine	Met	M	C₅H₁₁NO₂S	CH3-S-(CH2)2-CH(NH2)-COOH
Phenylalanine	Phe	F	C₉H₁₁NO₂	Ph-CH2-CH(NH2)-COOH
Proline	Pro	P	C₅H₉NO₂	NH-(CH2)3-CH-COOH
Serine	Ser	S	C₃H₇NO₃	HO-CH2-CH(NH2)-COOH
Threonine	Thr	T	C₄H₉NO₃	CH3-CH(OH)-CH(NH2)-COOH
Tryptophan	Trp	W	C₁₁H₁₂N₂O₂	Ph-NH-CH=C-CH2-CH(NH2)-COOH
Tyrosine	Tyr	Y	C₉H₁₁NO₃	HO-Ph-CH2-CH(NH2)-COOH
Valine	Val	V	C₅H₁₁NO₂	(CH3)2-CH-CH(NH2)-COOH

Structural details of the side chains: formula, 3D model and atoms nomenclature

The general formula of an amino acid is composed by a carbon alpha atom, a carboxyl group, a side chain group and an amino group.

Molecular formula: structural formula with the carbon alpha atom and the radical of each amino acid.
3D molecular model: a ball and stick model of the amino acids is shown. Oxygen, hydrogen, nitrogen and sulfur atoms are represented by colored spheres (Oxygen: red, Hydrogen: white, Nitrogen: blue, Sulfur: yellow). The carbon alpha atom is represented by black sticks and other carbons by grey sticks.
Atoms nomenclature:
- CA : Carbon alpha
- HB : Hydrogen of carbon beta
- HN : Hydrogen of nitrogen
- OXT : Oxygen of hydroxyl
- HXT : Hydrogen of hydroxyl
Representation of an amino acid example (cystein) engaged in a peptide chain and showing the carbone alpha and the carbone beta.

AMINO ACID	MOLECULAR FORMULA	3D MOLECULAR MODEL	ATOMS NOMENCLATURE
ALANINE
ARGININE
ASPARAGINE
ASPARTIC ACID
CYSTEINE
GLUTAMINE
GLUTAMIC ACID
GLYCINE
HISTIDINE
ISOLEUCINE
LEUCINE
LYSINE
METHIONINE
PHENYLALANINE
PROLINE
SERINE
THREONINE
TRYPTOPHAN
TYROSINE
VALINE