The Lysogenic Cycle: A Dormant Integration
1. Viral Entry: The virus, known as a temperate phage, enters the host cell.
2. DNA Integration: Instead of immediately replicating and destroying the cell (lytic cycle), the virus integrates its DNA into the host cell's genome. This integrated viral DNA is called a prophage.
3. Dormant Existence: The prophage replicates along with the host cell's DNA during normal cell division. The virus remains dormant, and the host cell continues to function normally.
4. Prophage Induction (Optional): Under certain environmental stresses (e.g., UV radiation, nutrient depletion), the prophage can be triggered to exit the dormant state and enter the lytic cycle.
Implications for the Host Cell:
* Viral Latency: The host cell lives and replicates normally, carrying the viral DNA within its genome.
* Potential for Lytic Cycle: The dormant prophage can reactivate, leading to the lytic cycle and the destruction of the host cell.
* Viral Spread: When the host cell divides, it passes the prophage on to its progeny, spreading the virus.
Key Differences from the Lytic Cycle:
* Dormancy: The lysogenic cycle involves a dormant stage where the virus doesn't immediately replicate and destroy the cell.
* Integration: The viral DNA becomes part of the host cell's genome.
* Progeny: The prophage is passed on to all offspring of the infected cell.
Examples:
* Bacteriophages: Many bacterial viruses can exist in a lysogenic cycle, contributing to bacterial diversity and evolution.
* Herpesviruses: Viruses like Herpes Simplex Virus (HSV) can enter a lysogenic cycle in human cells, causing latent infections that can reactivate under certain conditions (e.g., stress, illness).
In Summary:
The lysogenic cycle allows viruses to persist in a host cell without immediately causing harm. This dormant state can be long-lasting, but it can also lead to reactivation and the lytic cycle, ultimately resulting in cell destruction and the spread of the virus.
