Virus Notes Tobacco Mosaic Virus T4 Bacteriophage Influenza Virus
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
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
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
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 http://www.youtube.com/watch?v=wVkCyU5aeeU
Lytic Cycle Lytic Cycle Bacteriophage protein coat Bacteriophage DNA Bacterial chromosome Lytic Cycle Bacteriophage Bacteriophage DNA Bacteriophage protein
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 http://www.youtube.com/watch?v=_J9-xKitsd0
Lysogenic Cycle Lytic Cycle Lysogenic Cycle Bacterial chromosome Bacteriophage DNA Bacteriophage injects DNA into bacterium Lytic Cycle Lysogenic Cycle Prophage
Retroviruses (they’re coming back) Contain RNA Produce DNA copy of RNA May remain dormant for a period of time Some cancers, AIDS
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)
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