Download Viruses - Biology

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• What distinguishes ‘The Living’ from ‘The
Non-Living’?
Viruses
Big 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 cycle
Temperate 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.