Week 4B: Viral replication

Temperate stage

Can choose between lytic cycle or integrating into the host genome as a prophage

Virulent phage

Always follows the lytic cycle

Lytic cycle

Phage injects DNA → replicates → host cell lyses, releasing progeny.

• Fast and destructive

Lysogenic cycle

Phage DNA integrates into host chromosome as a prophage → replicated along with host genome without killing cell.

• Can later switch to lytic cycle under stress

Prophage therapy

The use of bacteriophages to treat bacterial infections

advantages: specific to target bacteria, effective against antibiotic-resistant strains

disadvantages: narrow host range, immune system clearance, regulatory approval

Viral attachment protein

Protein expressed on the surface of the virus

Receptor

A binding molecule present on the surface of the host cell

• Normally used for cell signaling and communication (but hijacked by virus facilitates attachment)

Host range

Set of species that the virus can infect

• Specificity of viral attachment protein and receptor interaction determines host range

Attachment of virus to receptors

Bacteriophages: attach to host receptors by viral attachments proteins on the tail fibers.

Enveloped viruses: attach by a specific viral protein embedded within the envelope

Some non enveloped viruses: attach by protein extending from the capsid

Other non enveloped viruses: attach by protein that forms part of the capsid itself.