Transcript Warm Up - Ms. Chambers' Biology

Virus Notes
T4 Bacteriophage
Tobacco Mosaic
Virus
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
Capsid
Surface
proteins
RNA
Membrane
envelope
What is a Virus?
T4 Bacteriophage
Head
DNA
Tail
sheath
Tail
fiber
• 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
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
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
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)
Viruses vs. Cells
Virus
Cells
Structure
DNA or RNA, capsid Cell membrane, cytoplasm
Reproduction
Only w/ host cell Cell division; asexual or sexual
Genetic Code
DNA/RNA
DNA
Growth &
Development
no
yes
no
yes
Obtain/Use
Energy
Response to
Environment
Change over
time
no
yes
yes
yes