Amino acids

Amino acids are the building blocks of which proteins are made. Simple proteins contain only amino acids, while conjugated proteins have additional components.

Twenty amino acids are specified by the genetic code and are utilized ribosome. They are:
Glycine    _____Serine_____    Asparagines_______    Histidine
Alanine _____   Threonine__    Glutamic acid______    Phenylalanine
Valine_____ _   Cysteine___     Glutamine________    Tyrosine
Leucine____      Methionine_     Arginine_________     Tryptophan
Isoleucine___    Aspartic acid    Lysine  ___________  Proline

Some additional amino acids have been isolated from some proteins. These are modification of the amino acids specified by the genetic code.

(i) Cystine, a double amino acid formed by linking of two cysteine molecules by a disulphide linkage.

(ii) Hydroxyproline, formed by the addition of a hydroxyl group to praline after the  protein has been synthesized.

(iii) Hydroxyl sine, similarly formed by addition of a hydroxyl group to lysine, Hydroxyproline and hydroxyl sine are found only in collagen and gelatin.

(iv) Thyroxin, formed from tyrosine in the thyroid gland and occurring only in the protein thyroglobulin elaborated from the gland.

(v) Diaminopimelic acid, a constituent of the mucopeptide of bacterial cell walls.

(vi) Desmosine and isodesmosine, modification of lysine found in elastin.

(vii) Mono-, di-, and tri-methyl lysines, modification of lysine found in histones and myosin.

(viii) 3-methyl histidine, a modification of histidine found in certain types of myosin.