Biology 40s Exam - Viruses

  1. characteristics of viruses
    • smaller than any living cell
    • can pass though filters
  2. how big are viruses
    • size ranges from 20-400 nm
    • only seen under electron microscopes
    • infect humans, animals, plants & bacteria
  3. are viruses alive
    • no, they can only replicate in living cells (can't reproduce on its own, must invade a host cell)
    • employ the host cell's replicative and metobolic pathways
  4. what are viral disease
    • animals: rabies, foot and mouth disease
    • humans: hepatitas, polio, influenza, AIDS and SARS
    • others: smallpox, yellowfever, chicken pox, measles and mumps, HIV, west nile, ebola, etc
  5. how do viruses take over a host cell
    • protein synthesis is how cells make proteins
    • 1. living cells carry all the genetic info (DNA) to make copies of themselves stored in chromosomes
    • 2. DNA molecules are copied into mRNA molecules to make proteins for the structure of the cell
    • 3. when cells divide they replicate their DNA to give two identical copies of the cell's DNA
  6. define viral replication
    • viruses carry DNA, they use it to make a few special proteins which 'hijack' the host cell and forces it to make new viruses
    • all viruses have a protein that recognizes the proper host cell
  7. what are the 2 types of cycles
    • lytic cycle
    • lysogenic cycle
  8. define lytic cycle
    • virus reproduces itself using the host cell's chemical machinery
    • virus injects its genetic material and 'tricks' the cell into replication which releases many viruses
  9. define lysogenic cycle
    • has a dormant phase
    • inside the host cell, some viruses do not reproduce right away
    • they mix their genetic instructions into the host cell's DNA, host cell reproduces, viral info does too
    • environmental or genetic signal will stir the 'sleeping' viral instructions
    • lysogenic cycle reverts back to the lytic cycle
  10. can viruses be cured
    • immunizations: work by pre-infecting the body with a weak or dead form of the virus so the body builds up antibodies to it
    • antibiotics have no affect
    • vaccines only work against viruses with non-varying proteins; if surface proteins mutate often, new changes aren't recognized
  11. what are the factors of how a virus is spread
    • Factors:
    • size of the population
    • number of days contagious
    • number of people came in contact with affected person
    • probability of contracting the virus
  12. what ways are viruses spread
    • airbourne
    • water
    • blood/bodily fluid contact
    • surfaces
  13. define epidemic
    • a widespread outbreak of an infectious disease
    • many people are infected at the same time
  14. define pandemic
    • an epidemic that is geographically widespread
    • occurring throughout a region or even throughout the world
  15. define endemic
    confined to a specific area
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Biology 40s Exam - Viruses