Practice Questions

Many medicines work by selectively inhibiting enzymes. Examples include drugs that inhibit bacterial enzymes or enzymes involved in cholesterol synthesis. The remaining options are biologically incorrect. Concept tested: Medical application of enzyme inhibitors.

Non-competitive inhibitors decrease the maximum reaction rate because some enzyme molecules become inactive regardless of substrate concentration. The other statements are incorrect. Concept tested: Effect on enzyme kinetics.

Excess substrate successfully competes with a competitive inhibitor, increasing enzyme activity. This effect is not observed with non-competitive or irreversible inhibitors. Concept tested: Experimental reasoning.

Many enzyme inhibitors regulate metabolic pathways by controlling enzyme activity. The other options do not represent normal biological roles of inhibitors. Concept tested: Physiological importance of inhibitors.

Heavy metals such as mercury and lead bind to sulfhydryl (-SH) groups, distorting enzyme structure and causing irreversible inhibition. The remaining options are incorrect mechanisms. Concept tested: Heavy metal inhibition.

Irreversible inhibitors form stable covalent or very strong bonds with enzymes, permanently inactivating them. Other options are inconsistent with irreversible inhibition. Concept tested: Irreversible inhibition.

Since increasing substrate fails to restore activity, the inhibitor likely binds outside the active site and changes enzyme conformation. Competitive inhibition would be overcome by excess substrate. Concept tested: Interpretation of experimental data.

Non-competitive inhibitors bind at an allosteric site, altering enzyme shape and reducing activity regardless of substrate concentration. Other options do not correctly describe this inhibition. Concept tested: Allosteric regulation.

Competitive inhibition is reversible because substrate molecules can outcompete the inhibitor at high concentrations. Non-competitive and irreversible inhibitors cannot be overcome this way. Concept tested: Effect of substrate concentration on inhibition.

Competitive inhibitors resemble the substrate and compete for the enzyme's active site. Increasing substrate concentration can overcome their effect. The other options describe irreversible inhibition or incorrect mechanisms. Concept tested: Competitive inhibition.