General Veterinary Biochemistry

AMINO ACIDS

• Amino acids are organic acids containing an amino group and a carboxyl group attached to the a – carbon atom.
• In addition to the amino and carboxyl groups, each amino acid contains a side chain, called R group, which is also attached to α- carbon atom. The side chain differs for each of the 20 amino acids.
• Amino acids are the monomers, which are used in the synthesis of proteins, which is a polymer. Each amino acid in a polypeptide chain is called as residue.
• The structure of an amino acid can be represented by the following formula

• The α-carbon atom of all the amino acids except glycine is attached to four different chemical groups and is therefore asymmetric in nature.
• Because of this asymmetric nature, amino acids exist in either in D or L configuration. They cannot be superimposed because they are mirror image of each other.
• The two forms of each pair are termed as stereoisomers, optical isomers or enantiomers.
• All the amino acids found in protein are of L configuration. The functions of the amino acids and their roles in protein structure are related mainly to the chemical properties of their side chain.
• D-amino acid: amino acids having D-configuration are also present in nature. They are not normally present in living organisms. Some of the D- amino acids are found in bacterial cell walls and in some antibiotics produced by bacteria. The antibiotic gramicidin-S is an example, which contains two D- phenylalanine residues.