Which of the following statements is not true for retroviruses? [2004]...
Retroviruses have RNA as the genetic material and hence they exhibit reverse transcription whereby DNA is synthesized on RNA template. They have reverse transcriptase as the enzyme.
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Which of the following statements is not true for retroviruses? [2004]...
Explanation:
The correct answer is option A: DNA is not present at any stage in the life cycle of retroviruses.
Retroviruses are a unique group of RNA viruses that have the ability to convert their RNA genome into DNA and integrate it into the host cell's genome. This process is called reverse transcription and is carried out by the enzyme reverse transcriptase, which is encoded by a gene carried by the retrovirus.
Life Cycle of Retroviruses:
1. Attachment and Entry:
- Retroviruses attach to specific receptors on the surface of host cells.
- The viral envelope fuses with the host cell membrane, releasing the viral core into the cytoplasm.
2. Reverse Transcription:
- The viral RNA genome is reverse transcribed into DNA by the enzyme reverse transcriptase.
- This process involves the synthesis of a complementary DNA strand using the viral RNA genome as a template.
- The resulting DNA molecule is known as the proviral DNA.
3. Integration:
- The proviral DNA enters the nucleus of the host cell and integrates into the host cell's genome.
- Integration is mediated by the viral enzyme integrase, which allows the proviral DNA to become a permanent part of the host cell's genome.
4. Transcription and Translation:
- Once integrated, the proviral DNA can be transcribed by the host cell's machinery into viral RNA molecules.
- These viral RNA molecules serve as templates for the synthesis of viral proteins by the host cell's ribosomes.
5. Assembly and Release:
- Viral proteins and genomic RNA molecules are assembled into new virus particles.
- The newly formed virus particles bud from the host cell, acquiring an envelope from the host cell membrane.
Why option A is not true:
Contrary to option A, DNA is present at a specific stage in the life cycle of retroviruses. The viral RNA genome is reverse transcribed into DNA during the process of reverse transcription. This DNA, known as the proviral DNA, is then integrated into the host cell's genome. Therefore, DNA is a crucial part of the retroviral life cycle.
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