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Download The Genetics of Viruses
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Chapter 19 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 A virus consists of a nucleic acid surrounded by a protein coat Genetic material ◦ DNA or RNA Capsid ◦ Protein coat surrounding nucleic acid Envelope ◦ Some; comes from host cell membrane Mode of entry ◦ Spikes, receptors, etc. Viruses replicate only in host cells 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 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 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 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
