FISH

MILK

MEAT

EGG

PROTEIN

About two-thirds of the total dry mass of a cell is composed of proteins

ELEMENT IN PROTEIN

CARBONHYDROGEN

OXYGEN

NITROGEN

Amino acids are the subunits of all proteins

There are 20 biological important amino acids

Each amino acid carries two functional group :

• A carboxyl group ( - COOH) which is acidic

• An amino group ( -NH2) which is basic

Two amino acids can combine to form a dipeptide by a condensation reaction

between the carboxyl group of one and the amino group of the other

The resulting a bond liking the two amino acids that is called peptide bond

Long chains of amino acids are called polypeptides

• The peptide bond can be broken by hydrolysis with heat, dilute acids or by enzymes

• The loss of the three dimensional structure of a protein molecule is known as denaturation

The linear sequence of amino acids in a

protein molecule. The first proteins to have its sequence of amino

acids determined was the hormone insulin

Peptide chain becomes folded or twisted forming a helix or pleated sheet. The structure is maintained by

hydrogen bonding.

Bending and twisting of the polypeptides helix into a

compact structure.

Structured is maintained by ionic, disulphide and

hydrogen bonding

Myoglobin, a protein found in muscles, has the tertiary structure.

Enzymes antibodies and many hormones have this structure

as well

Different polypeptide chains combine with associated non-protein groups forming a large complex protein molecule. Haemoglobin, an oxygen binding protein,

has a quartenary structure

Human can synthesis 11 of the 20 different amino acids used in

protein synthesis. These amino acids are known as non essential amino acids

Examples of non essential amino acids are proline, glycine, and

glutamic acids

The remaining nine amino acids cannot be synthesised in human. The must be

included in the diet. They are known as essential amino acids

Examples of essential amino acids are lysine, valine, leucine and tryptophan