Question

Refer to the given graph showing the relationship between temperature and enzyme action.

Select the correct statement regarding 'A' and 'B'.
(i) 'A' shows' rate at which reaction decreases due to denaturation of enzyme molecules.
(ii) 'B' shows the rate at which reaction increases due to decreased kinetic energy of the substrate.
(iii) As temperature rises, more and more enzyme molecules are denatured and 'A' appears to fall.
(iv) 'B' shows the rate at which reaction increases due to an increased kinetic energy of substrate and enzyme molecules.

• A. i, iii and iv
• B. iii only
• C. iii and iv only
• D. i and ii only

Answer 1

Answer: (A)

i, iii and iv

In this study, enzyme and substrate are treated with increasing temperature before they are mixed, and the rate of reaction is determined. Enzymes are mostly proteinaceous molecules. Proteins are denatured 'by heat, and the rate of denaturation increases and becomes significant at higher temperatures. When the enzyme is mixed with the substrate, with an increase in temperature the rate of reaction increases as there is increased kinetic energy of both substrate and enzyme molecules leading to more rapid movement and their collisions. However, with an increase in temperature denaturation of the enzyme occurs which is an irreversible destruction; eventually destroying the active sites. As a result, there is an apparent optimum temperature for the action of an enzyme due to dual effects, firstly, on the reaction and secondly, the stability of the enzyme protein.