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Viruses

Explore the characteristics, structure, and replication cycles of viruses like HIV and retroviruses. Discover how viruses cause diseases and genetic variations, leading to rapid evolution and infections. Learn about lytic and lysogenic cycles and the role of retroviruses in diseases.

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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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