Viruses. Evolution of Virus Alive or Not – Biologically inert – Unable to replicate genes –...
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Transcript of Viruses. Evolution of Virus Alive or Not – Biologically inert – Unable to replicate genes –...
![Page 1: Viruses. Evolution of Virus Alive or Not – Biologically inert – Unable to replicate genes – Unable to regenerate ATP – probably evolved as bits of cellular.](https://reader036.fdocuments.in/reader036/viewer/2022062315/5697bffb1a28abf838cc0c2e/html5/thumbnails/1.jpg)
Viruses
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Evolution of Virus
• Alive or Not– Biologically inert– Unable to replicate genes– Unable to regenerate ATP– probably evolved as bits of
cellular nucleic acid
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Structural Component of Virus
• small infectious particles • nucleic acid– Double or single stranded DNA– Double or single stranded RNA– Single circular molecule or linear
• Capsid– Protein shell
• some cases, a membranous envelope– Made from membrane of host cell
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Virus structure
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Obligate intracellular parasites• Replicate only in host cells
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Identification of a host cell
• Lock and key– Viral surface proteins and specific receptor
molecules of the host
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Bacteriophage
• Virus that infects bacteria• Bacterial Defenses– Natural selection– Restriction enzymes– Lysogeny• Co-exist
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Lytic vs Lysogenic
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Retrovirus
• Equipped with RNA transcriptase• RNA DNA• DNA can enter the nucleus into the host
genome• HIV
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Viral Infections in Animals
• Damage or kill cells• Produce toxins• Defense tools– Vaccines– Anti-viral drugs
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Viral infections in Plants
• Horizontal transmission– entering through damaged cell walls
• Vertical transmission– inheriting the virus from a parent
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Viroids and Prions
• Viroids – circular RNA molecules that infect plants and
disrupt their growth• Prions – slow-acting– virtually indestructible infectious proteins – brain diseases in mammals – mad cow– propagate by converting normal proteins into the
prion version