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