Question

The inhibitor which closely resembles the substrate in its molecular structure and inhibits the enzyme activity by binding to the active site of the enzyme is called

• A. feedback inhibitor
• B. non-competitive inhibitor
• C. competitive inhibitor
• D. allosteric modulator

Answer 1

Answer: (C)

In competitive inhibition, the inhibitor $(I)$ closely resembles the real substrate $(S)$, and is regarded as a substrate analogue. The inhibitor competes with substrate and binds at the active site of the enzyme but does not undergo any catalysis. As long as the competitive inhibitor holds the active site, the enzyme is not available for the substrate to bind. A competitive inhibitor diminishes the rate of catalysis by reducing the proportion of enzyme molecules bound to a substrate. At any given inhibitor concentration, competitive inhibition can be relieved by increasing the substrate concentration. Under these conditions, the substrate successfully competes with the inhibitor for the active site. Thus, competitive inhibition is usually reversible since the addition of more substrate tends to reduce the effect of the inhibitor. In competitive inhibition, the $K_m$ value increases whereas $V_{max}$ remains unchanged.