PROTEINS AND ENZYMES

PROTEINS

The term protein is derived from the word ‘proteios‘ meaning the ‘prime importance‘. This term was coined by Muller in 1838. These are the nitrogenous substances, i.e., have nitrogen along with C, H and O, and are called the ‘building blocks of the body‘.

All proteins are polymers of alpha-amino acids which are linked together through peptide linkage. Proteins make upto 15% by mass of our body. These are important components of most foods and are essential for nourishment purposes. Meat and eggs are the richest source of protein. In animals, 20 types of amino acid codes are found for the synthesis of proteins.

CLASSIFICATION OF PROTEINS

1- On the basis of composition, proteins are classified into following two classes.

• FIBROUS PROTEINS

They constitute structural materials of animal tissues. When the polypeptide chains run parallel and are held together by hydrogen and disulphide bonds, then fibre-like structure(fibrous protein) is formed . e.g., keratin, fibroin, collagen and myosin.

• GLOBULAR PROTEINS

They maintain and regulate the life cycle. In them, polypeptide chains are coiled about themselves which results in a spherical molecule. e.g., enzymes, hormones such as insulins and haemoglobins, etc.

2- On the basis of components of molecules, proteins are classified into following three classes.

• SIMPLE PROTEINS

These are made up of amino acids only. e.g., collagen of connective tissue, albumins, albuminade, globules, etc.

• CONJUGATED PROTEINS

These are made up of protein molecules joined to non-protein part(prosthetic group). e.g., haemoglobin, casein of milk, nucleoprotein, glycoprotein, phosphoprotein.

• DERIVED PROTEINS

These are formed by partial breakdown of natural proteins. e.g., peptones, insulin, fibrin, etc.

FUNCTIONS OF PROTEINS

1- They act as enzymes in plants and animals.

2- These are the components of hair, muscle and skin.

3- They act as hormones. e.g., insulin and vasopressin.

4- They transport oxygen, fats and other substances required for metabolism.

5- Proteins are vital for physiological growth and nourishment purposes. They help in the synthesis of cells, protoplasm and tissue culturing.

6- They provide instantaneous energy only at the time of emergency when carbohydrates and fats are not available.

7- These are also found helpful in the development of genetical characteristics and in controlling the hereditary activities.

DENATURATION OF PROTEINS

When protein is subjected to physical change such as change in temperature or chemical change such as change in pH, it loses its biological activity. This is called denaturation. The coagulation of eggs on boiling is a common example of denaturation.

ENZYMES

These are the complex nitrogenous organic compounds which are produced by living plants and animals. They are actually protein molecules of high molecular mass. These are also called biochemical catalysts because numerous reactions that occur in the bodies of animals and plants to maintain life processes, are catalysed by enzymes.

ENZYMES AND THEIR USES

• ZYMASE ENZYME– In the formation of ethyl alcohol from glucose.
• DIASTASE ENZYME– In the formation of maltose from starch.
• MYCODRUMI ACITI– In the production of vinegar from sugar beat.
• INVERTASE ENZYME– In the production of glucose and fructose from sugarcane.
• LACTO BACILLUS– In the production of lactic acid from milk.
• PEPSIN ENZYME– In the decomposition of protein into simpler amino acids in stomach.
• EREPSIN ENZYME– In the decomposition of proteins into amino acids in intestines.
• TRYPSIN ENZYME– In the decomposition of proteins into amino acids in pancreas.
• PTYLIN ENZYME– In the transformation of starch into glucose in mouth(saliva).
• CARBONIC ANHYDRASE– In the transformation of H₂CO₃ to H₂O and CO₂.
• NUCLEASES– In the transformation of DNA and RNA to nucleotides.
• AMYLASE– In the transformation of starch to alpha-glucose.
• UREASE– In the transformation urea to CO₂ and H₂
• RENNIN– Essential for the digestion of mother’s milk in young mammals.
• ALPHA-AMYLASE– In the production of sweet syrup from corn starch.

CHARACTERISTICS OF ENZYMES

1- Enzymes are highly specific in nature. e.g., Urease catalyses the hydrolysis of urea only.

2- Enzymes are highly active under optimum pH i.e., between 5-7.

3- Enzyme activity is increased in the presence of certain substances called co-enzymes.

4- Presence of metal ions increases the activity of an enzyme. e.g., amylase in the presence of Na⁺ ions are catalytically very active.

5- Presence of inhibitors and poisons reduces or completely destroys the catalytic activity of the enzymes.

6- Enzymes are highly active under optimum temperature i.e., 298-310K . On either side of optimum temperature, the enzyme activity decreases.

POINTS TO REMEMBER

• Enzyme catalysed reactions are faster than metal catalysed reactions.
• Disease albinism is caused due to the deficiency of enzyme tyrosinase.
• Enzymes are also used to treat heart diseases. e.g., enzyme streptokinase.
• Phenyl ketone urea disease is caused due to the deficiency of an enzyme phenylalanine hydroxylase.
• With only two exceptions, all enzymes are proteins but all proteins are not enzymes.
• Insulin which maintains level of blood sugar contains 51 amino acid units while haemoglobin which carries oxygen consists of 574 amino acid units.