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Chapter 19
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Non-living ◦ Non-cellular ◦ Cannot grow or reproduce on its own ◦ No metabolism Cause disease ◦ AIDS, colds, flu, measles, mono Cause cancer ◦ Cervical, leukemia T4 bacteriophages infecting an E. coli bacteria
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A virus consists of a nucleic acid surrounded by a protein coat
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Genetic material ◦ DNA or RNA Capsid ◦ Protein coat surrounding nucleic acid Envelope ◦ Some; comes from host cell membrane Mode of entry ◦ Spikes, receptors, etc.
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Viruses replicate only in host cells
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Viral replication that rapidly kills the host cell causing it to lyse or burst Involves 5 steps 1. Virus attaches to host cell membrane 2. Virus injects its DNA into host cell 3. Virus DNA inactivates host cell's DNA & uses host's raw materials & ribosomes to make viral DNA, capsids, tails, etc. 4. New viral parts are assembled into new viruses 5. Viral enzymes made by host lyse and release new viruses Transduction ◦ DNA from one bacteria (host) is transferred to another by a virus after a lytic cycle
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Viral replication that allows replication of the genome without killing the host Involves 3 steps 1.Bacteriophage infects bacteria cell and injects its DNA 2.DNA becomes incorporated into bacterial chromosome Prophage 3.Bacteria reproduces, making more copies of viral DNA Lytic cycle can be triggered
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Mutations ◦ Replicate rapidly, many errors ◦ Leads to evolution (sometimes quickly, like the flu) Recombination ◦ Viruses pick up genes from each other ◦ Can allow them to infect new hosts
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Contain RNA Reverse transcriptase enzyme uses the RNA to make DNA ◦ Normal flow of information is DNA RNA Protein ◦ Especially prone to errors in replication Use the host cell's ribosomes & raw materials to make viral proteins Cause some cancers & AIDS
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