Question

Flow of the events occurring in the lifecycle of retroviruses is :
A. Transcription
B. RNA-DNA hybrid formation
C. Reverse transcription
D. Integration
E. Translation
Choose the correct answer from the options given below :

• A. B, C, D, A, E
• B. C, B, D, A, E
• C. A, B, C, D, E
• D. D, C, B, A, E

Hint:

Central Dogma is DNA $\rightarrow$ RNA $\rightarrow$ Protein. Retroviruses work backward initially: RNA $\rightarrow$ DNA (Reverse Transcription), then integrate, then follow the normal path: DNA $\rightarrow$ RNA (Transcription) $\rightarrow$ Protein (Translation).

Answer 1

The Correct Option is B

Step 1: Concept:
The question asks to trace the specific biochemical steps that occur after a retrovirus (like HIV) infects a host cell.

Step 2: Step-by-step Explanation:

• Retroviruses contain an RNA genome. When they enter a cell, they must convert this RNA into DNA to hijack the host's cellular machinery.

• 1. Reverse transcription (C): The viral enzyme reverse transcriptase binds to the viral RNA genome to begin synthesizing DNA.

• 2. RNA-DNA hybrid formation (B): The immediate intermediate product of reverse transcription is a temporary double helix consisting of one viral RNA strand and one newly synthesized DNA strand. (The enzyme then degrades the RNA strand and synthesizes a second DNA strand to create double-stranded viral DNA).

• 3. Integration (D): The newly formed double-stranded viral DNA is transported into the host cell nucleus and permanently inserted (integrated) into the host's genomic DNA using the enzyme integrase. This forms a "provirus".

• 4. Transcription (A): The host cell's own RNA polymerase treats the viral DNA as native genes, transcribing it into viral messenger RNA (mRNA).

• 5. Translation (E): The host cell's ribosomes translate the viral mRNA into viral proteins, which assemble to form new viral particles.

• Therefore, the correct biological progression is: C $\rightarrow$ B $\rightarrow$ D $\rightarrow$ A $\rightarrow$ E.

Step 3: Final Answer:
The correct sequential flow of events is C, B, D, A, E, matching option (B).