Thursday, October 13, 2011

October 13, 2011

Today in class, we went through the notes about viruses and watched a video about the flu. Here's a basic overview of the notes.
Viruses: Living or non-living?
  • viruses are between life and non-life
  • Living characteristics: contain genes (RNA or DNA), are highly organized (complex protein structure
  • Non-living characteristics: not made of cells, cannot reproduce on thier own: viruses don't have the necessary structures to reproduce so they must use the structures of living cells


  • nucleic acid, the genetic material, is inside a protein coat
  • often include: head (where genes are held), tail, tail fibers

The virus in the animation on the left is called a T4 Bacteriophage. It is easy to see the structure of this virus.

Reproduction: Lytic and Lysogenic Cycles

Lytic Cycle

  1. virus injects genes into a host cell
  2. "hijacks" cell structures and uses them to make copies of itself
  3. viruses eventually causes the cell to lyse (burst)
  4. viruses are released to find a new host cell

Lysogenic Cycle

  1. virus injects genes into host cell
  2. viral genes are incorporated into normal cell genes
  3. genes are passed on without the cell making copies of the virus
  4. while in lysogenic cycle, cell does not lyse
  5. environmental changes will trigger the viral genes to switch to the lytic cycle

Plant Viruses

  • affect plants: interfere with growth and damages crops
  • most plant viruses have RNA not DNA
  • viruses are designed to get past plant epidermis and cell walls
  • no cure for the majority of plant viruses
  • humans have created plants that are resistant to certain viruses

Examples: Tobacco mosiac virus (TMV) and tomatoes, PRSV and papaya

Animal Viruses

  • many have a phosolipid outer layer, just like a cell's plasma membrane: allows viruses to slip in and out of the cell through endocytosis and exocytosis
  • reproduce in cell's cytoplasm: needs ribosomes to make viral proteins
  • RNA and DNA viruses
  • RNA viruses: HIV, mumps, common cold, polio
  • DNA viruses: chicken pox, herpes, hepatitis

HIV: the cause of AIDs

  • Retrovirus: reproduces by the use of viral DNA molecules
  • normally, cells use DNA to produce RNA (transcription)
  • HIV has cells use RNA to produce DNA (reverse transcription)
  • RNA then makes proteins
  • viral genes now in cell's genes, cell is producing viral proteins
  • Drugs for HIV: inhibit reverse transcription or inhibit production of the viral proteins

The full notes are on Moodle. The video we watched featured influenza, the flu, and was basically a review of the notes.

Homework: review viruses, moodle notes, work on group project script, work on textbook notes sheet


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