Transcript Viruses - North Mac Schools

Viruses- Are they alive?
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Acellular
Can not metabolize
Can’t grow or respond to environment
Can’t reproduce without host
• Discovery- Wendell Stanley- tobacco
mosaic virus
Virion- virus outside of cell
• Capsid-protein coat surrounding nucleic acid
• Genetic material- DNA or RNA
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dsDNA- double stranded DNA
ssDNA- single stranded DNA
dsRNA- double stranded RNA
ssRNA- single stranded RNA
• Super small amount of genes
• Capsomeres- Surface proteins- only attach to
particular host or even specific cells in the host
Enveloped virion
• Membrane acquired from its host cell
during viral replication or release
• Composed of phospholipid bilayer &
proteins- specific for host attachment
Bacteriophage
• Infects bacteria
• Replication– 2 cycles
Lytic Cycle-pg 390
(virulent-causes disease)
1. Attachment - the virus attaches itself to the host cell.
2. Injection - the virus inserts its genetic material into the
host cell.
3. Integration & Replication- the genetic material tells the
cell what to do & the host cell builds parts of the virus.
4. Assembly - the cell assembles the replicated parts into
new viruses.
5. Lysis - the cell breaks open and each replicated virus
can now infect other cells.
Lysogenic Cycle- pg 392
(temperate- doesn’t kill right away)
1. Attachment
2. Injection
3. Integration- virus DNA becomes part of
bacterial DNA- prophage
4. Replication- when host cell replicates its own
DNA, virus DNA is also copied
5. Assembly
6. Trigger > Lytic Cycle
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can be caused by sunlight, radiation, chemicals
Virus Life Cycle
• http://www.hhmi.org/biointeractive/hiv-lifecycle?utm_source=BioInteractive+News&
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Animations
• www.youtube.com/watch?v=wVkCyU5aee
U
• http://www.youtube.com/watch?v=_J9xKitsd0&feature=related
Viroids
• Small, circular pieces of RNA that are
infectious to plants
• Lack capsids
• May appear linear
Prions
• Not viruses because they lack nucleic acid
• Composed of single protein- PrP
– All mammals contain a gene that codes for
the a.a. sequence for cellular PrP
• Can re-fold into stable structures,
changing shape & become harmful
• Excess PrP or mutations cause the prion
PrP
• 40% of humans have PrP that can misfold