Abstract:
The term ‗amino acid‘ is generally understood to refer to the aminoalkanoic acids. They are
compounds containing an amino group( NH2) and a carboxylic acid group (-COOH) with
general formula H3N
(CR1R2)n COO
n = 1 for the series of amino acids, n = 2 for
amino acids series and n = 3 for amino acids series, etc.]. More than 700 amino acids
have been discovered in nature and most of them are amino acids. Bacteria, fungi algae
and plants are source for all these amino acids, which exist either in the free form or bound
up into larger molecules (as constituents of peptides, proteins, other types of amide, alkylated
and esterified structures). Among 700 amino acids twenty amino acids (actually, nineteen
amino acids and one imino acid) that are utilised in living cells for protein synthesis
under the control of genes are in a special category since they are fundamental to all life
forms as building blocks of peptides and proteins. The structures of the 20 most common
naturally occurring amino acids are shown in Table.1.1. All the amino acids except proline
contain a primary amino group. Proline contains a secondary amino group incorporated in to
a five-membered ring. The amino acids differ only in the substituent (R1 in general
formula, R2=H) attached to the carbon. The wide variation in these substituents is what
gives peptide and proteins their great structural diversity and is responsible for their great
functional multiplicity. Eight kinds of side chains (R1= aliphatic chain, hydroxyl containing,
sulphur containing, acidic, amides, basic, benzene containing and heterocyclic) are present in
the most common natural amino acids, in that ten are essential amino acids (denoted by red
asterisks (*) in Table
