What enzyme is activated at the BEGINNING of HIV infection (when HIV first enters the host cell)?

Correct answer: C. Reverse transcriptase

• A. INCORRECT — Integrase is the SECOND enzyme in the HIV replication cycle; it integrates the newly formed viral DNA into the host cell's chromosome.
• B. INCORRECT — HIV Protease acts LATE in the replication cycle, cleaving viral polyproteins into functional components during viral assembly and budding.
• C. CORRECT — After HIV enters a CD4+ T cell, the FIRST step is the conversion of HIV's RNA genome into double-stranded DNA using REVERSE TRANSCRIPTASE (an RNA-dependent DNA polymerase). This is the initial and defining step of retroviral replication.
• D. INCORRECT — RNA polymerase is a host cell enzyme; it transcribes the integrated viral DNA (provirus) into new viral RNA after integration — this occurs after reverse transcriptase and integrase have already acted.