The life cycle of an RNA virus involves attachment, entry, uncoating, replication, maturation, and release. These steps are crucial for the virus to infect a host cell and produce more viral particles.
Stages of the RNA Virus Life Cycle
Here's a breakdown of the typical life cycle stages of an RNA virus:
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Attachment: The virus binds to specific receptors on the surface of the host cell. This interaction is highly specific, determining which types of cells the virus can infect. This is a critical step as it initiates the entire infectious process.
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Entry: After attachment, the virus enters the host cell. This can occur through various mechanisms, including:
- Receptor-mediated endocytosis: The host cell engulfs the virus.
- Direct fusion: The viral envelope fuses with the host cell membrane.
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Uncoating: Once inside the host cell, the viral capsid (protein shell) disassembles, releasing the viral RNA genome into the cytoplasm.
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Replication: The viral RNA genome is replicated to produce more copies. The specific mechanisms depend on the type of RNA virus:
- Positive-sense RNA viruses: Their RNA genome can be directly translated into viral proteins by the host cell's ribosomes. These viruses often encode an RNA-dependent RNA polymerase (RdRp) which is used to make complimentary negative-sense RNA, which in turn serves as a template to make more copies of the positive-sense genome.
- Negative-sense RNA viruses: Their RNA genome must first be transcribed into a positive-sense RNA molecule by a viral RdRp before translation can occur.
- Retroviruses: These viruses (like HIV) use reverse transcriptase to convert their RNA genome into DNA, which is then integrated into the host cell's genome. The host cell then transcribes this viral DNA into RNA, which is used both as a template for more retroviral RNA and as mRNA to produce viral proteins.
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Maturation (Assembly): Newly synthesized viral RNA and viral proteins are assembled into new viral particles (virions). This process often occurs in specific locations within the host cell, such as the endoplasmic reticulum or Golgi apparatus.
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Release: The newly formed virions are released from the host cell to infect other cells. Release can occur through:
- Lysis: The host cell ruptures, releasing the virions (often resulting in host cell death).
- Budding: The virions bud from the host cell membrane, acquiring an envelope in the process. This process may not necessarily kill the host cell immediately.
