A peptide formation occurs due to a condensation reaction between the carboxylic (- COOH) group of one amino acid and amino (-NH2) group of another amino acid with the elimination of a water molecule.
This peptide bond is actually an amide bond of about 0.132 nm. Upon hydrolysis a peptide yields equal number of amino and carboxylic groups. This fact led to the suggestion that amino acids are linked to one another to form an amino acid polymer chain of polypeptide.
The polypeptide chain(s) fold appropriately into a protein. A peptide may be a dipeptide having only two amino acids or tri peptide having three amino acids or a variable number of amino acids.
If there are a few amino acids in a peptide chain it is known as oligopeptide and if there are many amino acids the peptide chain is a polypeptide.
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A peptide chain has an amino group at one end which is known as amino terminus or N-terminus. At the other end it has a carboxylic group and the end is known as carboxylic terminus or C-terminus.
Peptides participate in a number of biological activities:
1) In protein formation
2) As constituents of a group of compounds known as alkaloids.
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3) Serve as growth factors (Ex-Folic acid).
4) Peptide hormones are found in higher animals.
5) Peptides like glutathione act as co-enzyme.