What is the sequence which a retrovirus follows on entering a host cell?
The core concept here is the replication cycle of retroviruses, like HIV. The key steps after entering the host cell would be uncoating, reverse transcription, integration, and then viral protein synthesis. Wait, but the question is about the sequence after entry. So once the virus enters, the envelope fuses with the cell membrane, releasing the viral capsid. Then reverse transcriptase converts the viral RNA into DNA. That DNA is transported into the nucleus, where integrase integrates it into the host genome. After integration, the host's machinery transcribes the viral DNA into mRNA for protein synthesis.
The correct answer should be: entry, uncoating, reverse transcription, integration, and then viral protein synthesis. Let me check the options. The user didn't provide the options, but since the correct answer is given, I need to figure out the options based on that. Common distractors might include incorrect order of steps, like putting integration before reverse transcription, or skipping steps like uncoating.
For the wrong options, typical mistakes could be placing DNA synthesis before integration, or confusing the order of events after entry. For example, someone might think that after entry, the virus directly starts making proteins without reverse transcription. Others might reverse the order of integration and transcription.
The clinical pearl here is to remember that reverse transcription is a defining feature of retroviruses, distinguishing them from other viruses. Also, the enzyme reverse transcriptase is a key target for antiretroviral drugs.
I need to structure the explanation with each section as specified. The core concept is about the retrovirus replication cycle. The correct answer explanation should detail each step in order. Then, each wrong option is dissected by pointing out where the sequence is incorrect. Finally, a high-yield fact about reverse transcriptase and its role in antiviral therapy.
**Core Concept**
Retroviruses, such as HIV, replicate via a unique mechanism involving reverse transcription of RNA into DNA. After entering host cells, they follow a specific sequence: uncoating, reverse transcription, integration into the host genome, and viral protein synthesis.
**Why the Correct Answer is Right**
1. **Uncoating**: The viral capsid disassembles, releasing RNA and enzymes like reverse transcriptase.
2. **Reverse Transcription**: Reverse transcriptase synthesizes complementary DNA (cDNA) from the viral RNA.
3. **Integration**: The pre-integration complex transports cDNA into the host nucleus, where integrase inserts it into the host genome.
4. **Viral Protein Synthesis**: Host machinery transcribes integrated viral DNA into mRNA, which is translated into viral proteins for assembly and release.
**Why Each Wrong Option is Incorrect**
**Option A**: Reverses reverse transcription and integration. Integration occurs *after* reverse transcription, not before.
**Option B**: Omits uncoating, a critical first step to release viral components.
**Option C**: Places viral protein synthesis before integration. Protein synthesis requires the viral DNA to be integrated into the host genome first.
**Clinical Pearl / High-Yield Fact**
Reverse transcriptase is a defining enzyme of retrovir