SBI3U Viral Reproduction

Did you know? Tuberculosis is the biggest global killer of women. One third of Asian women are infected with TB.

Review What are the major structural components of a virus? Are viruses living things? Provide 4 examples of viruses. What’s the difference between an epidemic and a pandemic?

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Viral Reproduction Viruses can enter one of two life cycles: – Lytic cycle (active) – Lysogenic cycle (dormant)

Let’s take a look at the Lytic Cycle ideo/flash/bacteriophage.swf

Bacteria Cell Bacteriophage Host Genome 2. Virus injects its genome (DNA in this case) into the host 3. Virus’ DNA is incorporated into host’s DNA (genome). 1. Virus attacks and attaches to host cell

4. Viral DNA uses host’s enzymes to make copies of its DNA and more capsids

5. The new viral components (DNA & capsids) are assembled into 100 or so clones of the original invader

6. The newly assembled viruses produce lytic enzymes that causes host cell to lyse, releasing 100’s of new viruses.

7. New viruses are now free to infect more cells.

The Lytic Cycle The End?

Looking at your diagram… What’s different in the lysogenic cycle? –Virus attaches and injects its genome –The viral genome incorporates itself into the host’s genome [virus is called a provirus at this stage] –The viral genome will be replicated every time the host cell divides by mitosis –At this point, the virus is harmless –This can continue for years –In this case, the viral genome is not used to making viral copies yet. When the conditions are right, the viral genome will leave the host genome and enter the lytic cycle –Occurs with herpes and HIV (takes years for virus to become active)