Q.15 Which one of the following enzymes is encoded by human immunodeficiency virus (HIV)
genome?
(A) Reverse transcriptase (B) Phospholipase
(C) Phosphatase (D) ATP synthase
Reverse transcriptase is the enzyme encoded by the HIV genome. This retrovirus relies on its own genetic code to produce key proteins for replication inside host cells.
Option Analysis
Reverse transcriptase (A) is directly encoded by the HIV pol gene as part of a polyprotein precursor, enabling conversion of viral RNA into DNA during infection. Phospholipase (B) functions in host cell membranes for lipid breakdown but lacks any role in HIV replication or genome encoding. Phosphatase (C) removes phosphate groups in various cellular processes, yet no evidence shows it as an HIV-encoded enzyme. ATP synthase (D) generates cellular energy in mitochondria and is entirely host-derived, not part of the compact HIV genome.
Correct Answer
(A) Reverse transcriptase stands out as the essential viral enzyme for reverse transcribing RNA to DNA, a hallmark of retroviruses like HIV.
The human immunodeficiency virus (HIV) genome encodes a select group of enzymes critical for its replication cycle, with reverse transcriptase standing as the hallmark enzyme among options like phospholipase, phosphatase, and ATP synthase. This question tests core virology knowledge for competitive exams such as IIT JAM Biotechnology, where understanding retroviral genetics proves essential. Reverse transcriptase, produced from the pol gene, converts single-stranded viral RNA into double-stranded DNA, enabling integration into the host genome—a process absent in host enzymes.
HIV Genome Structure
HIV features a 9.7 kb single-stranded RNA genome organized into genes: gag (structural proteins), pol (enzymes including reverse transcriptase, protease, integrase), and env (envelope glycoproteins). The pol gene translates as a polyprotein cleaved by viral protease to yield functional reverse transcriptase (p66/p51 heterodimer), which carries DNA polymerase and RNase H activities for RNA degradation during reverse transcription. No phospholipase, phosphatase, or ATP synthase genes appear in this compact viral blueprint.
Why Reverse Transcriptase?
Unlike eukaryotic cells, HIV must supply its own reverse transcriptase since hosts lack this RNA-to-DNA capability. The enzyme initiates replication post-entry: tRNA^Lys3 primes minus-strand DNA synthesis, followed by strand transfer and plus-strand completion. Inhibitors like AZT target this enzyme, underscoring its therapeutic importance. Phospholipase aids lipid signaling but plays no direct viral role; phosphatase regulates phosphorylation unrelated to HIV; ATP synthase powers host ATP production via oxidative phosphorylation.
Exam Relevance for IIT JAM
For IIT JAM aspirants in Biotechnology or Life Sciences, this MCQ highlights retroviral life cycles. Key takeaway: Viral enzymes like reverse transcriptase distinguish pathogens from host machinery. Practice similar questions on HIV replication to master enzyme functions, gene products, and drug targets.
