PROTEINS

PROTEINS

INTRODUCTION: Next to water, protein is the most abundant component of the body. It accounts for about a sixth of the live body weight and a third of it is found in the muscles, a fifth in the bones and cartilage, a tenth in the skin and the remainder in other tissues and body fluids.

There are thousands of different specific proteins in the body, each having a unique structure and function. For this reason, the word protein implies not one but a large group of complex compounds.

Proteins are present in all living tissues, both plant and animal. They are essential to life because vital parts of the nucleus and protoplasts of every cell are proteins. 

COMPOSITION: Proteins are very large organic compounds. Proteins, like carbohydrates and fats, contain carbon, hydrogen and oxygen. In addition, proteins contain about 16 percent nitrogen, which is their unique feature and distinguishes them from carbohydrates and fats. Some proteins also contain sulphur and sometimes phosphorous, iron and cobalt. Proteins are  more complex than fats and carbohydrates, as the size of the molecule is large and there  is a great variation in the units from which it is formed.

Plants are the primary source of proteins in nature. Proteins are synthesized by the plants from the nitrates and ammonia in the soil. Herbivorous animals use plant proteins to meet theier protein needs. Man uses plant foods as also animal foods (milk and  meat) to meet his protein needs. Nitrogen is returned to the soil through degradation of products of animal metabolism, excretion of  nitrogen compounds in urine and faeces, and decomposition of animal body at leath, to complete the natural nitrogen cycle.

STRUCTURE AND CLASSIFICATION

There are three structures of proteins as follows:

1. Primary structure
2. Secondary structure
3. Tertiary structure.

There are three types of proteins:

1. Simple proteins
2. Conjugated proteins
3. Derived proteins.

FUNCTIONS

The primary function of proteins is tissue building.

Proteins are the main solid matter in muscles, they are also the major constituents of blood, matrix of bones, teeth, skin, nails and hair. Our body, which consists of about 60 percent water and 19 percent fat is held together by only 17 percent proteins and 4 percent minerals.

The principal functions of proteins in the body are discussed below.

1. Body-building and building a new tissues
2. Maintenance of tissues
3. Regulatory functions
4. Proteins as precursors of enzymes, hormones and antibodies
5. Transport of Nutrients
6. Special functions of amino acids

i)                    Glycine

ii)                  Histidine

iii)                Phenylalanine

iv)                Milk formation

v)                  Energy supply

Table: Sources of Protein

Food	Units recommended for adults	Protein
		g per unit	g in unit recommended
Cereals- rice, wheat, millets & their products	10	2-3	20-30
Dals, Pulses	2	0-6	10-12
Milk, Curd, etc.	1-2	5	5-10
Eggs	0-1	0-6	0-6
Meat, Fish, Poultry	0-1	5-6	0-6
Vegetables
Leafy green	1	1-2	1-2
Beans and Peas	1	2-4	2-4
Roots, Tubers & others	1	1	1
Fruits (Vitamin C-rich)	1	1	1