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VIRUS

VIRUS. In what kingdom do we classify a virus? None! Viruses are not considered living, so we do not classify them with living organisms. What Is a Virus?. Viruses are non-living particles Do not have all the criteria for life DO NOT GROW, DO NOT DEVELOP, DO NOT CARRY OUT RESPIRATION

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VIRUS

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  1. VIRUS

  2. In what kingdom do we classify a virus? None! Viruses are not considered living, so we do not classify them with living organisms.

  3. What Is a Virus? • Viruses are non-living particles • Do not have all the criteria for life • DO NOT GROW, DO NOT DEVELOP, • DO NOT CARRY OUT RESPIRATION • Viruses do reproduce, but only with the help of a host cell. • Smaller than bacteria • One drop of blood can contain six billion viruses

  4. Virus Naming • Not named in the same way as organisms. • No genus/species scientific names • Some are named after their diseases they cause. • Ex. Poliovirus causes polio • Other viruses were named for the organ or tissue they infect. • Ex. Adenovirus infects the adenoid tissue, which causes the common cold.

  5. Virus Naming • Some viruses are given a code because there are similar viruses that infect the same host. • Seven similar-looking viruses infect E. Coli (Bacteria) • Code T1- T7 (T = Type) • Bacteriophage – A bacteria infected with a virus.

  6. Viral Structure • Viruses has an inner core of nucleic acid • DNA or RNA, which is injected into host cells. • The nucleic acid is protected by and outer coat of protein called a capsid. • Large viruses may have an additional layer called an envelope. • Composed of lipids, carbohydrates, and proteins. Ex. HIV

  7. Viral Structure • 4 different shapes

  8. Polyhedral Papilloma Virus Capsid Nucleic Acid

  9. Helical Shape Nucleic Acid Capsid 376,200x

  10. EnvelopInfluenzavirus A Capsid found inside. Envelope

  11. Bacteriophage

  12. Attachment • Must recognize and attach to a receptor site found on the plasma membrane of the host cell. • Lock and Key model, envelops and capsids • Virus’s protein interlocks with the correct molecular shape on the receptor site. • Fools the cell into thing it is something the cell needs • Bacteriophage: Tail fibers attach to host cell

  13. Attachment • Viruses are cell specific • Only can attach to certain kinds of cells • T4 can only attach to E. coli • Cannot infect animals, plants, or other bacteria • Polio can only infect human intestinal and never cells. • Few viruses can infect many organisms • Ex. Flu virus

  14. Viral Replication Cycle • Virus enters the host cell and takes over its metabolism. • One of two ways • Lytic Cycle • Lysogenic Cycle

  15. Lytic Cycle • Once inside, the virus’ genes become active and will take over the host cell’s genetic material. • Viral genes force the host cell to make new viruses. • The host cell’s enzymes, raw materials and energy are used to make copies of the virus.

  16. Lytic Cycle (2) • New viruses exit the host cell by bursting it. • The host cell is killed • Takes about 20 mins. & makes about 200 new viruses.

  17. Lysogenic Cycle • Begins the same way as the Lytic Cycle • Does not immediately take over, cell lives • The virus’s nucleic acid becomes integrated into the host cell’s chromosome, virus is now a Provirus • Cell carries on with its own metabolic activity; Mitosis. Daughter cells will contain the Provirus.

  18. Lysogenic to Lytic • The provirus can be inactive from a few weeks to years. • Ex. Herpes simplex I virus, cold sores • Once the provirus is activated (may be activated by stress), the Lytic cycle begins and the cell dies

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