XII Chemistry BIEK Topic - Proteins (Short Note)

Proteins (Short Note)
Definition
Proteins are polymers of amino acids in which different amino acids are linked together through peptide bonds.




Explanation
Proteins consists of one or more polypeptides chain. In general, protein molecules consist of forty to ten thousands or more amino acids units.

The word protein is derived from the Greek word Proteios which means first or of primary importance, in fact proteins are the primary materials of life.

Proteins have very high molecular mass, for e.g. the molecular mass of egg albumin is about 43,000 a.m.u and that of serum albumin is 7,000 a.m.u.

Plants form Proteins from the simple inorganic substances and phosphates. Animals cannot synthesize proteins from inorganic substance. Therfore, they depend upon plants and other animals for dietary Proteins. Animals prepare their own proteins from simple organic molecules. Proteins are necessary for growth and for maintaining existing tissues.




Classification of Proteins
Millions of kinds of proteins exist. The human body may contain as many as five million different kinds of Proteins.

Commonly proteins are classified into the following three classes.

1. Simple Proteins

2. Conjugated Proteins

3. Derived Proteins


1. Simple Proteins

The Proteins which on hydrolysis gave only amino acids or their derivatives, are called simple proteins. They are further classified into following six classes.


a. Albumins

These Proteins are water soluble, and are coagulated by heat. They may be precipitated by saturating their solution with Ammonium Sulphate.

For Example, Egg albumin and serum etc.


b. Globulins

These Proteins are insoluble in water but soluble in dilute salt solution and in dilute solution of strong inorganic acids and basis. They are coagulated by heat.

For Example, Serum Globulins and tissues etc.


c. Prolamins

These Proteins are insoluble in H2O or salt solution, but are soluble in dilute acids and alkalis.

For Example, Zein, Gliadin and Hordein etc.


d. Glutelins

These Proteins are insoluble in water or dilute salt solution but are soluble in the dilute acids and basis. These are coagulated by heat.

For Example, Glutelin and Oryzenin etc.


e. Albuminoids

These Proteins are insoluble in water or salt solution but are soluble in concentrated acids and base.

For example, Keratins and Fibroin etc.


f. Basic Protein

These proteins are strong basic.

For example, Keratins and Fibroin etc.


2. Conjugated Proteins

Those Proteins which contain a non proteinic group attached to the proteinic group are called conjugated proteins. The non proteinic group is called Prosthetic group. This group may be separated from the proteinic part by careful hydrolysis.

Conjugated Proteins are further divided into the following five groups.


a. Nucleo Proteins

The prosthetic group is a nucleic acid. This protein is present in the nuclei of living cell.


b. Chromo Proteins

These are coloured protein. The colour is due to the prosthetic group.


c. Glyco Proteins

In these proteins the prosthetic group contains a carbohydrate or a derivative of carbohydrate.


d. Lipo Proteins

In these proteins prosthetic group is a lipid.


e. Phospho Protein

In these proteins the prosthetic group contains a phosphoric acid.


3. Derived Proteins

The derived proteins are the degradation products obtained by the action of acids, bases or enzymes on proteins. These includes peptones polypeptides and Proteose.