| Consider a chemical reaction in which substrate A is enzymatically converted to product. The rate of change of substrate to product with increasing concentration of substrate is shown by broken line. The rate of reaction with increasing concentration of substrate A with a fixed amount of substance B is shown by unbroken line. |
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| If the same reaction is carried out with fixed quantity of substrate and increasing concentration of B, the expected result will be: |
A)
B)
C)
D)
Correct Answer: C
Solution :
| The graph given in question shows that in the presence of a given amount of enzyme the rate of an enzymatic reaction increases as the substrate concentration increases until a limiting rate is reached after which further increase in the substrate concentration produces no significant change in the reaction rate (broken line). This maximum rate of reaction is known as the maximum velocity or \[{{V}_{\max }}\]when fixed amount of substance B is added and concentration of substrate A is increased the reaction reached its normal \[{{V}_{\max }}\] but it took a higher concentration of substrate to get it there. This means\[{{V}_{\max }}\]of the reaction (unbroken line) remained unchanged whereas the substrate concentration at 1/2 the maximum velocity or \[{{\operatorname{K}}_{m}}\] is increased. A higher \[{{\operatorname{K}}_{m}}\] corresponds to a lower affinity for the substrate. This means the affinity of substrate A is decreased in the presence of substance B which is a competitive inhibitor of A. If the same reaction is carried out with fixed quantity of substrate and increasing concentration of B \[{{V}_{\max }}\] will be highest at zero concentration of substance B but with increase in its concentration most of the active sites of enzyme will be bound by substance B instead of its substrate A leading to decrease in the rate of reaction with increase in the concentration of substance B. |
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