Virus, or “Poison” Virus, or “Poison” Is it alive? Not really… Is it alive? Not really… Depend on cells to reproduce Depend on cells to reproduce obligate intracellular parasites obligate intracellular parasites Inert organic particles when Inert organic particles when outside cells outside cells Viruses for all - infect bacteria, Viruses for all - infect bacteria, protists, and all higher plants protists, and all higher plants and animals and animals Infect Infect specific cell types specific cell types in host in host Virus size comparison at Cellsalive.com
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Virus, or “Poison” Is it alive? Not really… Depend on cells to reproduce obligate intracellular parasites Inert organic particles when outside.
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Virus, or “Poison”Virus, or “Poison”
Is it alive? Not really…Is it alive? Not really… Depend on cells to reproduce Depend on cells to reproduce obligate obligate
intracellular parasitesintracellular parasites Inert organic particles when outside cellsInert organic particles when outside cells Viruses for all - infect bacteria, protists, Viruses for all - infect bacteria, protists,
and all higher plants and animalsand all higher plants and animals Infect Infect specific cell typesspecific cell types in host in host
Virus size comparison at Cellsalive.com
Edward Jenner – 1700’s, Smallpox vaccine
Vaca = Cow,
noticed milkmaids immune to smallpox
Louis Pasteur – rabies vaccine, 1800’s
Wendell Stanley – crystallized TMV (Tobacco Mosaic Virus), 1900’s,
showed that viruses are NOT small bacteria
Viruses - StructureViruses - Structure nucleic acid nucleic acid (RNA or DNA) – instructions (RNA or DNA) – instructions
for making proteinsfor making proteins protein protein capsidcapsid may have plasma membrane, or may have plasma membrane, or envelopeenvelope Surface proteins for attachment to host Surface proteins for attachment to host
cellcell Little or no Little or no metabolism:metabolism:
Who will read the DNA/RNA and make viral proteins that Who will read the DNA/RNA and make viral proteins that assemble into a viral capsid?assemble into a viral capsid?
If a virus has an envelope (membrane), where does it come If a virus has an envelope (membrane), where does it come from?from?
The host cell
The host cell’s plasma membrane
Influenza Virus
Surface proteins(protein)
(nucleic acid,instructions formaking proteins)
(membrane from host cell)
Criteria used to Classify Viruses
1.Type of nucleic acid 2.Presence or absence of an envelope3.Shape/morphology of the capsid4.Specific surface proteins different strains
Lytic Cycle:Cells lyses and releasesnew viral particles
Viral Replication by Host Cell
2. Entry
3. Replication
4. Assembly5. Lysis / Cytolysis
1. Adsorption
Lysogenic Cycle:Period of dormancyuntil stimulus causeslytic cycle
Viral Replication by Host Cell
Integration of viral DNA into host’s DNA Provirus (in this case a prophage)
Viral Replication by Host Cell
(compare & contrast based on lecture diagrams)Lytic Cycle Lysogenic Cycle
1. Viral DNA/RNA transcribed and translated by host cell
2. Cells lyse and releasesnew viral particles
1. Period of dormancyuntil stimulus causes cell to transcribe and translate viral DNA (viral DNA is incorporated into cell’s DNA)
2. Cells lyse & release new viral particles
RetrovirusesRetroviruses
RNARNA core core Replication – cells make viral Replication – cells make viral
DNA from RNA (reverse DNA from RNA (reverse order)order)