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Amino acids

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

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 ser GLYCINE gly
THREONINE ALANINE ala
TYROSINE tyr CYSTEINE (1) cys
ASPARAGINE asn VALINE val
GLUTAMINE gln LEUCINE leu
ISOLEUCINE ile
PROLINE pro
METHIONINE met
PHENYLALANINE
TRYPTOPHAN trp
Amino acids with charged side chains

Charged side chains are POLAR.

ACIDIC SIDE CHAINS BASIC SIDE CHAINS
ASPARTIC ACID asp LYSINE
GLUTAMIC ACID glu ARGININE arg
HISTIDINE his
  1. (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.
    cystein
AMINO ACID MOLECULAR FORMULA 3D MOLECULAR MODEL ATOMS NOMENCLATURE
ALANINE alanin alaST alaWF1
ARGININE arginin argST argWF1
ASPARAGINE asparagin asnST asnWF1
ASPARTIC ACID asp aspST aspWF1
CYSTEINE cystein cysST cysWF1
GLUTAMINE glutamin glnST glnWF
GLUTAMIC ACID glu gluST gluWF1
GLYCINE glycin glyST glyWF
HISTIDINE histidin hisST hisWF1
ISOLEUCINE ile isoST isoWF1
LEUCINE leucin leuST leuWF1
LYSINE lysin lysST lysWF1
METHIONINE met metST metWF1
PHENYLALANINE phe pheST pheWF1
PROLINE prolin proST proWF1
SERINE serin serST serWF1
THREONINE threonin thrST thrWF1
TRYPTOPHAN trp tryST tryWF1
TYROSINE tyrosin tyrST tyrWF1
VALINE valin valST valWF1