Question

Zidovudine acts by which of the following mechanism?

• A. Protease inhibition
• B. DNA polymerase inhibition
• C. Nucleoside reverse transcriptase inhibition
• D. Fusion inhibition

Hint:

Antiretroviral drugs against HIV are grouped by which step of the virus life cycle they block. Knowing a drug's class tells you its target enzyme.

Answer 1

The Correct Option is C

Concept:
Antiretroviral drugs against HIV are grouped by which step of the virus life cycle they block. Knowing a drug's class tells you its target enzyme.

Step 1: Zidovudine (AZT) is a nucleoside analogue. Inside the cell it is converted to its active triphosphate form.

Step 2: This active form looks like a normal building block of DNA, so the viral enzyme reverse transcriptase incorporates it while copying viral RNA into DNA. Because zidovudine lacks the 3'-OH needed for the next link, the growing DNA chain stops. So it acts as a nucleoside reverse transcriptase inhibitor (NRTI).

Why the others are wrong: Protease inhibitors (e.g., ritonavir) block the maturation enzyme, not reverse transcriptase. Fusion inhibitors (enfuvirtide) stop the virus entering the cell. Human DNA polymerase is not the main target. Zidovudine specifically targets reverse transcriptase as a nucleoside analogue.

Answer: Option (3) — Nucleoside reverse transcriptase inhibition.