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AlexiaCastillo Ch19 (pathogens in animals and plants- less complex…
AlexiaCastillo Ch19
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animal viruses
replication- can replicate only inside host cells. One key variable is double or single strand DNA/ RNA, presence or absence of membrane envelope.
viral envelopes- (membranous outer layer) uses it to enter the host cell . outside of these envelope are viral carbohydrates attached to polypeptide (glycoproteins), they bind to specific receptor molecules o the surface host cell
viral genetic material- there are 3 types of single stranded RNA genomes found in animal viruses. Common classification system based on their genetic material, double or single stranded DNA or double or single stranded RNA
HIV (human immunodeficiency viruses)- typically of a retroviruses. contain 2 identical molecules of single stranded RNA and 2 molecules of reverse transcripts
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reverse transcriptase- have enzymes that transcribes an RNA template into DNA, information flow is opposite of the usual direction
provirus- integrated DNA never leaves the host genome, remaining a permanent resident of the cell
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viruses structure- looking at viruses more closely we can identify that they are consisting of nucleic acid enclosed in protein coat. Some of them are surrounded by a membranous envelope.
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capsids and envelopes-
viral envelopes- outer structure or coat that encloses the nucleic capsids of some viruses that mature by budding through the membrane cell; may contain lipoprotein
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replication of viruses
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lack metabolic enzymes and equipment for making proteins such as ribosome. Can only replicate within a host cell.
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cycle of phages- best understood viruses, some of them are most complex. Double stranded DNA viruses replicate by 2 alternative mechanisms
lytic cycle- phage replicative cycle that culminates in death of the host cell. Last stage of infection, bacterium lyses(breaks open) and releases phages that were produced within the cell
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lysogenic cycle - instead of lysing host cells, phages coexist with them in state called lysogenic. lytic cycle kills the host cell allows replication of the phage genome without destroying the host
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prophage- the genetic material of a bacteriophage, incorporated into the genome of a bacterium and able to produce phages if specifically activated
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