PROTIENS

Proteins are made up of large number of amino acids linked together chemically.

Proteins are most complex chemical compounds formed of C, H, O,N, S, P. The characteristic element is the nitrogen . All the reactions in the body are controlled by proteins, known as enzymes.

Proteins are made up of some 20 different naturally occurring amino acids linked together chemically. They are polymers made up of chains of amino acids. These amino acids are linked by peptide bond or peptide linkage. During digestion, these proteins are broken down into amino acids and absorbed through the intestinal wall.

Sources of Proteins- Principal sources of  proteins are pules, meat, fishes,eggs, milk soya bean, cereals, etc.

Daily Requirements- An adults person needs on an average about 70-100gm of proteins per day. The growing children and protein. Approximately 15% of proteins should be present in human diet.

Categories of proteins: On basis of chemical nature, proteins are divided into three categories -

(a) Simple proteins - These are formed of peptide chains ans yield only amino acids on hydrolysis. examples are albumin, globulin, histones, protamines, etc.

(b) Conjugated proteins - These are the proteins formed in combination with glucose (glycoproteins), lipid(lipoproteins), phosphate (phosphoprotein0, etc. examples are casein, blood antigens, haemoglobin of RBCs, etc

(c) Derived proteins -  These are the protiens which are formedby partial hydrolysis of simple proteins. examples are peptones, proteoses, etc.

AMINO ACIDS-  Proteins are the polymers made up of chains of amino acids. Thus amino acids are building blocks of protiens. many amino acids are linked one another to form protein. hence, amino acids are called monomers of proteins. It consists following characteristics:

1. These are the basic units of protiens.
2. All amino acids have at least one acidic caboxylic group (- COOH) and one basic amino group(-NH2).
3. These are colorless, crystalline solids.
4. These are soluble in water and insoluble in organic solvents.

Examples of amino acids are alanine, glycine, serine, leucine, isoleucine, etc. the simplest amino acid is glycine.

Formation of peptide bond: A peptide bond is formed when two amino acids are joined together by a peptide bond. A polypeptide is formed when numbers of successive amino acids are joined together in a long chain of peptide bond.

Categories of amino acids : There are 20 types of amino acids. on tha basis of nutritional value, they are divided into two categories.

(i) Essential amino acids : These are the amino acids which are not synthesized in the body. therefore, they must be included in diet. These are leucine, isoleucine, lysine, phenylalenine, trytophan, valine, methionine, and threonine. These are eight in number.

(ii) Non essential amino acids - These are the amino acids which are synthesized in the body. they may or may not be present in the diet. These are alanine, serine,glycine, glutamine, tyrosine, asparatic acid, cysteine, arginine, histidine, proline, glutamic acid and asparagine.

Functions of protein: Proteins as building blocks- Many proteins act as structural proteins ans take part in building and repairing of the body tissues. Therefore, these are essential for the growth.

1. Proteins as energy - Proteins provide energy fuel. The caloric value of 1 gm of protein is 5.654 kcal while the physiological fuel value of 1gm of proteins is 4.0 kcal.
2. Proteins as enzymes - These act as enzymes or bio-catalyst which regulate life processes. Nearly 2000 different kinds of enzymes are known as far.
3. Protein as hormones - Some hormones are  proteins, such as insulin (a hormone regulating glucose balance).
4. Protein as defensive - Some proteins are antibodies or immunoglobins. They neutralize the foreign bodies and develop immunity.

     5.  Thrombin and fibrirogen cause blood clotting.

Diseases due to protein deficiency - The proteins are essentials for the body growth. their deficiency in the diet causes retardation of physical growth and mental growth. Deficiency of proteins causes two diseases in infants; marasmus and kwashiorker.