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Concept Breakdowns

Viral Replication Lytic vs Lysogenic Pathway

Flashcards on the lytic and lysogenic viral replication pathways — two distinct strategies bacteriophages use to replicate inside host bacteria. A key topic for AP Biology, USMLE Step 1, and general microbiology courses, understanding these cycles clarifies how viruses cause acute infection versus latent persistence.

Interactive Deck

5 Cards
1
Front

What happens in the lytic cycle?

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The phage injects DNA → host replicates phage DNA and proteins → cell lyses, releasing 100–200 new phage particles. The host cell is destroyed in the process.

2
Front

What happens in the lysogenic cycle?

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2
Back

Phage DNA integrates into the host chromosome as a prophage. The bacterium replicates normally, passing the prophage to daughter cells. Lysis is triggered later by stress signals.

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Front

What is a prophage?

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A prophage is bacteriophage DNA integrated into the bacterial chromosome during lysogeny. It replicates with the host and can be induced to enter the lytic cycle by UV radiation or DNA damage.

4
Locked

What triggers lytic induction from lysogeny?

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Lytic vs lysogenic: key differences

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Frequently Asked Questions

What is the difference between lytic and lysogenic cycles?

The lytic cycle results in immediate host cell destruction and release of new phage particles. The lysogenic cycle involves integration of phage DNA (prophage) into the host genome, allowing the virus to remain dormant.

  • Lytic: fast, destructive, acute infection
  • Lysogenic: slow, latent, can switch to lytic

How do bacteriophages decide between lytic and lysogenic pathways?

The decision depends on phage gene expression and environmental signals. High multiplicity of infection, low nutrients, or specific regulatory proteins (like lambda CI repressor) favor lysogeny. Favorable host conditions often favor the lytic cycle.

What is the significance of lysogeny in human disease?

Lysogeny allows bacteria to acquire new virulence genes through lysogenic conversion. Classic examples include Corynebacterium diphtheriae (diphtheria toxin), Vibrio cholerae (cholera toxin), and S. pyogenes (erythrogenic toxin) — all encoded by prophages.