Occurrence

• Peptides occur in every living organism and play a crucial role in fundamental biochemical and physiological functions of life. They appear in the form of hormones, enzymes, receptors and antibiotics.
  
  

Synthesis

• Peptides are synthesized either through liquid-phase peptide synthesis or solid-phase peptide synthesis. Both methods involve the coupling of amino group or N-terminus of one amino acid to carboxyl group or C-terminus of another.
  
  

Peptide Classes

• There are four major classes of peptide: ribosomal peptides, non-ribosomal peptides, peptones and peptide fragments. Ribosomal peptides are assembled by translation of messenger RNA. Non-ribosomal peptides are synthesized by specific enzymes, instead of mRNA; peptones are derived from meat or animal milk; and peptide fragments refer to protein fragments.
  
  

Functions

• Peptides are essential in several fundamental physiological and biochemical reactions of life. Synthetic peptides are useful ingredients in the preparation of cross-reacting antibodies. They are also applied in the design of novel enzymes.
  
  

Application of Synthetic Peptides

• Synthetic peptides are used to develop new peptide-based hormones, immunogens, vaccines and drugs.