PROTEIN

Proteins are organic macro molecule found in all living organism. They are polymers formed form condensation of amino acids joined by peptide linkings and have the molecular weight of the chain that exceeds 10 000. Proteins contain the elements carbon, hydrogen, oxygen and nitrogen. Many protein also contain sulphur and phosphorus.

AMINO ACIDS

An amino acid contains a basic amino group (-NH₂) an acidic carboxyl group (-COOH) a hydrogen atom and a R group are covalently linked to the same carbon atom. The R group varies in different amino acids . There are 20 amino acid which occur naturally in the protein of living organism. The various combinations of different amino acid produce a various protein. The amino acid act as buffer which help maintenance  the environment of body internal fliud because protein are amphoteric molecules. Each amino acid has its own specific pH at which it will exist in zwitterion form. The isoelectric point of amino acid is the pH that cause this electrical neutrality. Essential amino acid are amino acid that cannot be synthesised in the body and which must be included in the diet. Non essential amino acid can be synthesised from other amino acid in the body provide there is adequte total dietery proteins. 

PEPTIDES AND POLYPEPTIDES

The amino acid group is joined to the carboxyl group of other amino acid by a peptide bond ina condensation reaction to form a dipeptide. The bond linking the two amino acids is called peptide bond. Succesive condensation of amino acid form a polypeptide chain. The proces called polymerisation. A protein molecule consist of one or more polypeptides.

CLASSIFICATION OF PROTEINS

Some common methods used to group proteins are based on:

Levels of organisation – Primary, secondary, tertiary, and quarternary  structures.

Structures – fibrous and globular proteins.

Composition – simple and conjugated protein

Functions – structural, catalysis, signals, movement, defense and storage.