Proteins which are used as a catalyst in biochemical reaction are known as biocatalysts.
Enzymes have following two specific characters as :
(i) Specificity (ii) Efficiency
Specificity of enzymes
(a) Generally, one enzyme can catalyze only one biochemical reaction.
(b) It can increase the rate of reaction upto 1020 times.
(c) In some cases one enzyme can catalyze more than one reaction and one reaction can be catalyzed by more than one enzyme. eg. Enzymes present in Yeast (Zymase) can ferment both glucose and fructose into alcohol and also cane-sugar can be hydrolysed by invertase and sucrase enzymes.
Efficiency of enzymes:
(a) One molecule of enzyme can convert millions of substrate molecules into product per second.
eg. Carbonic anhydrase enzyme present in red blood cells has the highest turn over number.
(b) With having tertiary structure it can be collected as crystals.
Enzymes are denatured at higher temperatures.
(c) Enzymes can be stored at low temperature as they are inactivated.
Importance of enzymes
In the thousands of enzymes present in body if even a single enzyme would be absent or damaged then complex disease results in.
eg. Scarcity of Phenylalanine hydroxylase enzyme in human body results in Phenylketonuria disease.
Factors affecting enzyme action:
(i) Optimum temperature and pH. Enzyme catalysed reactions have maximum rate at physiological pH of around 7.4 and human body temperature of 37ºC (310 K) under one atmosphere pressure.
In fact, as the temperature or pH is increased, the rate rises to a maximum (at 37ºC or pH = 7.4) and then falls off.
(ii) Enzyme activators (coenzymes). The activity of certain enzymes is increased in the presence of certain substances, called co-enzymes. It has been observed that if a protein contains a small amount of vitamin as the non-protein part, its activity is enhanced considerably. The activators are generally metal ions such as Na , Mn2+ , Cu2+ , Co2+ etc. These metal ions are weakly bonded to the enzyme molecules and increase their catalytic activity. For example, the enzyme, amylase in presence of NaCl, which provides Na+ ion, shows a very high catalytic activity.
(iii) Enzyme inhibitors and poisons. Just as in the case of catalysts, the activity of enzyme is slowed down in the presence of certain substance. Such substances are called inhibitors or poisons. They act by combining with the active functional group thereby reducing or completely destroying the catalytic activity of the enzymes. The use of many drugs is on account of their action as enzyme inhibitors in our body.
Sodium, Potassium and Chlorine
(i) Na+ is the principal mineral cation in the extracellular fluid.
(ii) K + is the principal cation inside the cell.
(iii) Cl- is the principal mineral anion in the ECF.
(iv) Na+ and K+ are essential to the maintenance of water balance and acid-base balance.
(v) Na+ and K+ are important in nerve impulse transmission.
Calcium and Phosphorus
(i) Calcium and phosphorus are deposited in bones and teeth to give them strength and rigidity.
(ii) Ca2+ is also essential for blood coagulation, neuromuscular function, cardiac function and actions of many enzymes and hormones.
(iii) Phosphorus enters into many compounds such as nucleic acids and phospholipids, many co-enzymes and high energy compounds like ATP.
(iv) Calcium plays an essential role in sustaining intestinal peristalsis and growth of body tissues.
(i) Iron is required for haemoglobin synthesis.
(ii) Iron is essential both for transportation of oxygen to tissues and for operation of oxidative systems within the tissue cells.
(i) Magnesium is required as a catalyst for many intracellular enzymatic reactions, particularly those relating to carbohydrate metabolism.
(ii) Mg is the central metal atom in chlorophyll.
Iodine is used in the synthesis of thyroid hormones.
(i) Zinc is a constituent of carbonic anhydrase, present in RBCs helping in CO2 transport.
(ii) Zinc is a component to lactic dehydrogenase, important for the interconversion between pyruvic acid and lactic acid.
(iii) Zinc is a component part of some peptidases and therefore is important for digestion of proteins in the alimentary canal.
(i) Cobalt helps in erythropoiesis and in the activities of some enzymes.
(ii) It is present in vitamin B12 .
(i) Copper helps in the utilisation of iron.
(ii) Copper deficiency may produce anaemia because of failure in iron utilisation.
(i) Molybdenum is a constituent of oxidase enzymes (xanthine oxidase).
(ii) Molybdenum plays an important role in biological nitrogen fixation.
(i) Fluorine maintains normal dental enamel and prevents dental caries.
(ii) Excessive intake of fluorine cause fluorosis characterized by mottled teeth and enlarged bones.
It has been observed that certain organic compounds are required in small amounts in our diet but their deficiency causes specific diseases. These compounds are called vitamins.
Classification of Vitamins-
Vitamins are classified into two groups depending upon their solubility in water or fat.
(i) Fat soluble vitamins:
Vitamins which are soluble in fat and oils. But insoluble in water are kept in this group. These are vitamins A, D, E and K. They are stored in liver and adipose (fat storing) tissues.
(ii) Water soluble vitamins:
B group vitamins and vitamin C are soluble in water so they are grouped together. Water soluble vitamins must be supplied regularly in diet because they are readily excreted in urine and can not be stored (except vitamin B12) in our body.
Some important vitamins, their sources and diseases caused by their deficiency are listed in table.
Name of Vitamins
Vitamin A (Retinol)
Fish liver oil, carrots, butter and milk
Xerophthalmia (hardening of cornea of eye) Night blindness
Yeast, milk, Green Vegetables and cereals and grams
Beri beri (loss of appetite, retarded growth)
Vitamin B2 (Riboflavin)
Milk, egg white, liver, Kidney
Cheilosis (fissuring at corners of mouth and lips), digestive disorders and burning sensation of the skin
Vitamin B6 (Pyridoxine)
Yeast, milk, egg yolk, cereals and grams
Meat, fish, egg and curd
Pernicious anaemia (RBC deficient in haemoglobin)
Vitamin C (Ascorbic acid)
Citrus fruits, amla and green leafy vegetables
scurvy (bleeding gums)
Vitamin D (Calciferol)
Exposure to sunlight, fish and egg yolk
Rickets (bone deformities in children) and osteomalacia (soft bones and joint pain in adults)
Vitamin E or Tocopherol (α, β and γ) or Anti Sterility factor
Eggs, Milk, Fish, Wheat germ oil cotton seed oil etc.
Sterility (loss of sexual power and reproduction)