The lysogenic and lytic cycles are two distinct methods by which bacteriophages (viruses that infect bacteria) replicate and propagate. Here's a breakdown of the differences between the two:
Lytic Cycle:
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Definition: The lytic cycle is a viral replication process that results in the destruction of the host cell.
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Steps:
- Attachment: The virus attaches to the surface of the host bacterium.
- Entry: The viral DNA or RNA is injected into the host cell.
- Replication: The host’s cellular machinery is hijacked to replicate the viral genome and synthesize viral proteins.
- Assembly: New viral particles are assembled from the replicated viral components.
- Lysis: The host cell is lysed (broken open), releasing new virions into the environment.
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Outcome: The host cell is destroyed, and multiple new virus particles are released to infect other cells.
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Timeframe: The lytic cycle is relatively quick, often completing within minutes to hours after infection.
Lysogenic Cycle:
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Definition: The lysogenic cycle is a viral replication process that allows the virus to integrate its genetic material into the host's genome without destroying the host cell immediately.
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Steps:
- Attachment: Similar to the lytic cycle, the virus attaches to the host.
- Entry: The viral DNA is injected into the host cell.
- Integration: The viral DNA integrates into the host genome and becomes a prophage.
- Replication: The host cell divides, copying the prophage along with its own DNA. This can continue for many generations without harming the host.
- Induction (optional): Under certain conditions (such as stress to the host cell), the prophage may excise itself from the host genome and enter the lytic cycle.
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Outcome: The host cell is not immediately lysed and can continue to live and reproduce, carrying the viral DNA with it.
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Timeframe: The lysogenic cycle can last for long periods, with the prophage being passed on through multiple generations of host cells.
Summary of Differences:
- Destruction of Host Cell: The lytic cycle results in the death of the host cell, while the lysogenic cycle does not immediately kill the host.
- Viral Replication: In the lytic cycle, the virus replicates and assembles new virions quickly. In the lysogenic cycle, the viral genome is integrated into the host genome and replicated passively with the host's DNA.
- Timeframe: The lytic cycle is rapid (minutes to hours), whereas the lysogenic cycle can last for years as the prophage remains dormant.
In essence, the key distinction lies in the immediate outcome for the host cell and the method of viral replication.