Current Affairs 11th Class

Category : 11th Class

Substrate concentration : If there are more enzyme molecules than substrate molecules, a progressive increase in the substrate molecules increases the velocity of their conversion to products. However, eventually the rate of reaction reaches the maximum. At this stage the active sites of all the available enzyme molecules are occupied by the substrate molecules. Therefore, the substrate molecules occupy the active sites vacated by the products and cannot increase the rate of reaction further.

Enzyme concentration : The rate of reaction is directly proportional to enzyme concentration. An increase in enzyme concentration will cause a rise in the rate of reaction up to a point and them the rate of reaction will be constant. Increasing the enzyme concentration increases the number of available active sites.

Product concentration : Accumulation of the product of enzyme reaction lowers the enzyme activity. Enzyme molecules must be freed to combine with more substrate molecules. Normally the product are quickly removed from the site of formation and the reaction does not suffer.

Hydrogen ion concentration (pH) : Some enzyme act best in an acid medium, other in an alkline medium, for every enzyme there is an optimum pH where its action is maximum e.g., 2 for pepsin, 6.8 for salivary amylase, 8.5 for trypsin. Most enzyme show maximum activity in a pH range of about 6.0 to 7.5 i.e., near neutral pH (endoenzymes). A shift to the alkaline or acid side rapidly decreases the enzyme activity and finally stops it altogether. This is due to denaturation of enzyme molecule i.e., change in its physical structure.

Temperature : Within certain limits \[(5-40{}^\circ C)\] the rate of an enzyme catalyzed reaction increases as the temperature increases. The \[{{Q}_{10}}\] of most enzymatic reactions is 2, i.e., every 10°C rise in temperature doubles the rate of reaction. Most enzymes show maximum activity in a temperature range of 25 to 40°C. Beyond this temperature, there is sharp fall in the rate of reaction.

Modification in the physical form of the enzyme results in the loss of its catalytic activity. This change in structure is called denaturation of protein. This is the permanent change, and the denatured enzyme protein remains inactive even if the temperature is then brought down. The enzymes are not destroyed by freezing, and regain their lost activity if the temperature is raised to normal.

Deep freezing of food for preserving them for long periods is done not only to prevent the growth and multiplication of microorganisms but also to inactivate enzymes. It makes impossible for the microorganisms to digest the food.

Enzyme inhibitors : Certain chemical compounds inhibit activity of enzyme molecules either permanently or temporarily. Thus, di-isopropyl flurophosphate (DFP) inhibits the action of various enzymes catalysing hydrolysis of ester linkage. Inhibition is permanent or irreversible.

Poisons and Radiation : Poisons such as cyanide and radiation destroy the tertiary structure of the enzymes, making them ineffective.