Basic Principels of Peptide

Peptide is the condensation of two Alpha amino acid to form a dipeptide, bond between two alpha amino acids called peptide bond.
Amino acids can be covalently bonded together into a polymer by the formation of a amide bond (the peptide bond) between the alpha carboxyl group of one Amino acids and the alpha-amino of the next Amino acids.
A molecule of water is eliminated for each peptide bond formed and the products is called a peptide (e.g. dipeptide below). The portion of the Amino acids left in the peptide is terned an amino acid residue.

What is Peptide?

The resulting Co (Called as Carboxyl)-NH (Called as Amide Group) linkage is known as peptide bond. Polymen composed of two, three, a few (3~10) and many amino acids residue are known, respectively, dipeptide, tripeptide, oligopeptide and polypeptide.
Proteins are molecules that consists of one or more polypeptide chains.

A molecule containing two amino acids joined by a peptide bond is a Dipeptide; one with three amino acids held together by two peptide bonds is a Tripeptide; four is a Tetrapeptide; etc. In general, Peptides contain 12 or fewer amino acid residues. An Oligopeptide contains between 12 and 20 amino acids and a Polypeptide contains greater than 20 amino acids. Twenty appears to be a magic number with respect to peptide/protein structure. Oligopeptides with 20 or fewer amino acids do not fold into, do assume a single low energy conformation, rather they exist in numerous random shapes. Molecules with greater than 20 amino acids very often fold into a single stable conformation, a single low energy conformation. The terms polypeptide and protein are often used interchangeably. However, the term protein is often reserved for molecules that perform some cellular function.