Which enzyme is inhibited by nucleoside reverse transcriptase inhibitors used in HIV therapy?

• A. DNA polymerase
• B. Reverse transcriptase (RNA-dependent DNA polymerase) of HIV
• C. RNA polymerase
• D. Protease

Answer: (D)

Nucleoside reverse transcriptase inhibitors block the HIV reverse transcriptase, the enzyme that copies the virus’s RNA genome into DNA. These drugs resemble natural nucleosides and are incorporated into the growing viral DNA chain by HIV’s RNA-dependent DNA polymerase (reverse transcriptase). Once a faulty nucleoside is incorporated, DNA chain elongation stops, preventing the virus from completing its replication cycle.

This is why the enzyme being inhibited is the HIV reverse transcriptase. They don’t target the viral protease (which processes viral proteins later in the life cycle), nor do they inhibit cellular RNA polymerases in a way that would halt viral replication. While some NRTIs can affect mitochondrial DNA polymerase gamma as a side effect, their primary, intended target in HIV therapy is reverse transcriptase.