VirusesBig Questions:What is a virus?

How does a virus function?

What a virus is…

• “Obligate Intracellular Parasite”– Cannot carry out life

cycle independent of a cell host

• Composed of:– Genome: DNA or RNA – Protein coat: Capsid

• Host can be: any cell (prokaryote or eukaryote)

How big is a virus?

Prokaryotic Viruses

• PHAGES! (bacteriophages)• 2 kinds:

Virulent phages: Lytic life cycleTemperate phages: Lysogenic life cycle

Eukaryotic Viruses

• More diverse than phages– DNA or RNA genomes– Double or single stranded – Can have lipid envelope around protein coat

• RNA viruses (retroviruses) mutations are very common, so permanent immunity not possible

Eukaryotic Viral Replication

Host cell eventually wears out making so many

viruses!

• These medicines help people with HIV, but they are not perfect. • They do not cure HIV/AIDS. People with HIV infection still have the virus in their

bodies. • They can still spread HIV to others through unprotected sex and needle sharing,

even when they are taking their medicines.

Can Viruses Be Used to Help Not Harm?

• Yes! Gene Therapy. Inserting new genes into cells.

Phages are being used to kill bacteria where using antibiotics may not be helpful.

How to get new DNA into Virus?

TRANSDUCTION

Plant Viruses

• Plants get viruses too!• Look like “blotchy” pigment patterns

What viruses are not…

• Viruses are not the most simple kinds of infections:– Viroids: Disease causing RNA molecules in plants– Prions: Disease causing protein molecules • Mad Cow, CJD in humans, scrapie (sheep)

Questions to answer!1. Explain why viruses could be considered living or non-living

depending on particular aspects of their function.2. Explain how different types of viruses utilize the information

system of cells to complete their life cycles.3. Compare bacteriophages and eukaryotic viruses.4. Compare lytic and lysogenic cycles of viral reproduction.5. Explain the structure and function of HIV.6. How do viral processes increase genetic variation in

organisms?7. Compare viruses to other infectious particles.