Classification of Amino Acids


On the basis of their synthesis in animal body, amino acids are classified into 3 groups.

  • (a)   ESSENTIAL AMINO ACIDS  These amino acids cannot be synthesized in animal body, and therefore must be present in their diet. For example, in human being essential amino acids are valine,isoleucine,phenylalanine, methionine, leucine, lysine, tryptophan and threonine. (remember it as VIP,MLL,TT)
  • (b)  NON ESSENTIAL AMINO ACIDS.  These amino acids can be synthesized in animal body and may not be supplied in the diet. For example alanine, arginine, tyrosine, asparagin,glutamine, proline etc . In plants all the  amino acids are  non essential.
  • (c)  SEMI ESSENTIAL AMINO ACIDS.  These amino acids are synthesized at a slower rate than their requirement in the body , e.g. arginine  and histidine.

On the basis of the nature of their side chains, amino acids are classified into the following categories.:

(i)              Amino acid aliphatic, hydrophobic side chains e.g. Gly, Ala, Val, Ile, Pro.

(ii)     Amino acid with aromatic hydrophobic side chains.e.g. Phe, Tyr, Trp. Trypophan has indole ring and benzene ring. The tyrosine is less hydrophobic than the other two because it contains a – OH group.

(iii)       Amino acid with sulphur containing hydrophobic side chains, e,g, cysteine (cys or C ) and methionine (met or M).

(iv)       Amino acid with aliphatic hydroxyl side chains e.g.,Serine (Ser or S), Threonine (Thr or T).

(v)           Amino acid with basic side chains e.g.. Lysine (k), arginine (R) histidine (H)

(vi)        Amino acid with acidic side chains e.g. Aspartic acid (asp or D) and Glutamic acid(Glu or E) Asparagine (asu.N) and Glutamine (Glu or Q) are uncharged derivatives a terminal amide group.