Question

An example of competitive inhibition of an enzyme is the inhibition of
A. Succinic dehydrogenase by malonic acid
B. Cytochrome oxidase by cyanide
C. Hexokinase by glucose-6-phosphate
D. Carbonic dehydrogenase by carbon dioxide

Answer 1

Hint:-Inhibitors are the chemical compounds that decrease or stop the biological activity of the enzymes and this phenomenon is called inhibition. This inhibition is of two types- competitive and non-competitive inhibition.

Complete answer:
Competitive inhibition is when the inhibitor molecules show structural similarity to the substrate molecules so both compete to bind at the active site, then stable enzyme-inhibitor complex is formed and enzyme activity is reduced as the enzyme is not able to form complex with substrate.
A classic example of competitive inhibition is succinic acid dehydrogenase that oxidizes succinic acid to fumaric acid. If the concentration of malonic acid is added, the activity of succinic acid dehydrogenase decreases rapidly. Hence malonic acid acts as a competitive inhibitor since it has structural resemblance to succinic acid. The action of competitive inhibitors can be reversed by increasing the concentration of the substrate. Non-competitive inhibition is when the inhibitor is not structurally similar to the substrate molecule so there is no competition for the active sites of the enzymes by the inhibitor and it fixes itself at the allosteric site of an enzyme. This alters the physical structure of the enzyme. For example, cyanide poisoning results in inhibition of cytochrome oxidase which is essential for nearly all mammalian cells. This type of inhibition cannot be reversed by increasing the concentration of the substrate.
Thus, the right option is A.

Note:- Competitive inhibitors are used to control the bacterial pathogens by using the sulpha drugs like sulphanilamide which works as competitive inhibitors of folic acid synthesis in bacteria as they substitute p-amino benzoic acid.