Peptide bonds of protein

All proteins yield amino acids when hydrolyzed and all but two of these are α-amino carboxylic acids. Proline and hyroxyproline are α-imino acids.

In proteins, amino acids are united through amide linkages between the α-carboxyl and α-amino functional groups of adjacent amino acid residues. Such bonds are called peptide bonds. Linkage of many amino acids through peptide bonds results in an unbranched chain called a polypeptide. Each component amino acid in a polypeptide is called a “residue” or “moiety”.

Proteins thus have a repeating backbone from which 20 different possible kinds of side chains protrude.

Chemically, the peptide bond is a covalent bond that is formed between a carboxylic acid and an amino group by the loss of a water molecule. In the cell, the synthesis of peptide bonds is an enzymatically controlled process that occurs on the ribosome and is directed by the mRNA template.

The peptide bond has a partial double-bond character, that is, it is shorter than a single bond and is rigid and planar. The bonds between the α-carbons and the α-amino or α-carboxyl groups can be freely rotated and this allows the polypeptide chain to assume a variety of possible configuration.

A peptide chain has directionality because its two ends are different. There is an N-terminal end and a C-terminal end. By convention, the direction of the peptide chain is always

N-terminal end S C-terminal end 

The N-terminal end is always on the left, and the C-terminal end is always on the right.
Peptide bonds of protein