Note: In the following questions a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.

Assertion : Enzymes have active sites that hold substrate molecule for a chemical reaction.

Reason : Drugs compete with natural substrate by attaching covalently to the active site of enzyme.

• Enzymes do have active sites that hold substrate molecules for certain chemical reaction in a living organism.

• This active site of enzymes usually holds the substrate molecule at a suitable orientation so that the substrate can interact with the reagent molecules.

• Substrates bind to the active sites through ionic bond, H-bonding, van der Waals interaction or dipole-dipole interaction.

Whereas, drugs inhibit the activities of enzymes by blocking the active sites & prevent the binding of the substrate to the site and thus disrupts the catalytic activity of enzymes.

• Therefore, drug’s competition with the suitable natural substrates by attaching covalently to active site of enzyme cannot be the reason for the given assertion statement.