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Viruses (Virus Replication (viral genome enters host cells in various ways…
Viruses
Virus Replication
- viral genome enters host cells in various ways
- once inside, virus begins to replicate itself
- Virus uses host enzymes, ribosomes, tRNAs, amino acids, ATP, and other molecules
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- candidates for the source of viral genomes are plasmids and transposons
- because viruses are OIP, its safe to assume they evolved as bits of cellular nucleic acid
Lytic Cycle
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- produces new phages and breaks the host's cell wall (releasing the viruses)
- phage replicative cycle that kills the host cell
Lysogenic Cycle
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- Viral DNA molecule is incorporated into the host cell's chromosome (prophage)
- replicates the phage genome without killing the host
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Virus - infectious particle consisting of genes held in protein coat.
much simpler in structure that proks
cannot reproduce/carry out metabolism outside of host cell
"borrowed life"
- tobacco mosaic disease (TMV)
crystallization of the infectious particle in 1935 (Wendell
Stanley)
- because viruses are OIP, its safe to assume they evolved as bits of cellular nucleic acid
Virus - infectious particle consisting of genes held in protein coat.
much simpler in structure that proks
cannot reproduce/carry out metabolism outside of host cell
"borrowed life"
Viral composition
Bacteriophages
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- A protein tail piece injects the phage DNA into host
- elongated capsid head that encloses their DNA
- viruses that infect bacteria
Capsids/Envelopes
- capsids are protein shells that enclose the viral genome
- built from protein subunits called capsomeres
- variety of structures; associated viruses are called helical or icosahedral viruses
- serves as accessory structure that helps infect hosts
- viral envelopes are a combination of viral and host cell molecules
- Viral glycoproteins on the envelope bind to specific receptor molecules on the surface of a host cell
Viral Genomes
- classified as either DNA viruses or RNA viruses
- either a single linear or circular molecule of the nucleic acid
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- Viruses have between three and 2,ooo genes in their genome
- consists of either single/double stranded DNA or single/double stranded RNA
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- a virus is a nucleic acid enclosed in a protein coat and in some cases, a membranous envelope. NOT CELLS.
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- Viruses are obligate intracellular parasites (can replicate only in host cell)
- each virus has a host range (limited number of host cells it can infect)
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