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Viruses

Viruses. Chapter 19. What do you know about viruses?. Viral Characteristics. 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. 19.1.

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Viruses

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  1. Viruses Chapter 19

  2. What do you know about viruses?

  3. Viral Characteristics • 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

  4. 19.1 A virus consists of a nucleic acid surrounded by a protein coat

  5. Viral Structure • Genetic material • DNA or RNA • Capsid • Protein coat surrounding nucleic acid • Envelope • Some; comes from host cell membrane • Mode of entry • Spikes, receptors, etc.

  6. 19.2 Viruses replicate only in host cells

  7. Lytic Cycle • Viral replication that rapidly kills the host cell causing it to lyse or burst • Involves 5 steps • Virus attaches to host cell membrane • Virus injects its DNA into host cell • Virus DNA inactivates host cell's DNA & uses host's raw materials & ribosomes to make viral DNA, capsids, tails, etc. • New viral parts are assembled into new viruses • 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

  8. Lysogenic Cycle • Viral replication that allows replication of the genome without killing the host • Involves 3 steps • Bacteriophage infects bacteria cell and injects its DNA • DNA becomes incorporated into bacterial chromosome • Prophage • Bacteria reproduces, making more copies of viral DNA • Lytic cycle can be triggered

  9. Viruses & Genetic Variation • 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

  10. Retroviruses • 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

  11. HIV Infection

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