1. Virus Notes
Tobacco Mosaic
Virus
T4 Bacteriophage
Influenza Virus

2. What is a Virus? DNA or RNA core Protein coat around outside (capsid)
They infect living cells & make them produce more viruses
Very, very small and very sweet!
Influenza Virus
RNA
Capsid
Surface
proteins
Membrane
envelope

3. What is a Virus? Virus proteins bind to cell surface receptors
Specific to cells they infect they can only bind to cells that they “fit” with
Bacteriophages – viruses that infect bacteria
T4 Bacteriophage
Head
Tail sheath
DNA
Tail fiber

4. How big is a virus? Here is how you can imagine the size of viruses:
If a virus was the size of a basketball:
A bacterium would be as large as a city block
A grain of sand would be two miles long
A person would be 4,000 miles tall

7. Lytic Infection Virus enters cell
Uses the cells machinery to make copies of itself
Causes the host cell to be lysed (burst open)
Example – Bacteriophage T4

8. Lytic Cycle Lytic Cycle Bacteriophage protein coat Bacteriophage DNA
Bacterial
chromosome
Lytic Cycle
Bacteriophage
Bacteriophage DNA
Bacteriophage protein

9. Lysogenic Infection Virus enters cell
Viral DNA (prophage) integrates w/ host DNA meaning the DNA enters into the host DNA by splicing
Viral DNA replicated w/ host DNA
Does not lyse (kill) host cell initially
Example – Bacteriophage lambda

10. Lysogenic Cycle Lytic Cycle Lysogenic Cycle Bacterial
chromosome
Bacteriophage DNA
Bacteriophage injects DNA into bacterium
Lytic Cycle
Lysogenic Cycle
Prophage

11. Retroviruses (they’re coming back)
Contain RNA
Produce DNA copy of RNA
May remain dormant for a period of time
Some cancers, AIDS

12. Are they Living or Nonliving?
Take 3 minutes and create a chart comparing viruses & cells on these points
Structure (what is it made of?)
Reproduction (how?)
Genetic code (DNA or RNA?)
Growth & Development (can it grow and change?)
Obtain and use energy (yes or no)
Respond to Environment (yes or no)
Change over time (yes or no)

13. Response to Environment
Viruses vs. Cells
Virus
Cells
Structure
Reproduction
Genetic Code
Growth & Development
Obtain/Use Energy
Response to Environment
Change over time
DNA or RNA, capsid
Cell membrane, cytoplasm
Only w/ host cell
Cell division; asexual or sexual
DNA/RNA
DNA
yes no no
yes no
yes
yes
yes