Ch13 study guide BIO205

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Ch13 study guide BIO205
2013-03-25 20:01:03
Ch13 study guide BIO205

Ch13 study guide BIO205
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  1. General characteristics of viruses
    • acellular
    • lack cell membrane
    • lack most characteristics of life: 
    • cannot carry metabolic pathways
    • can neither grow nor respond to environment
    • cannot reproduce independently
    • makes cures elusive
  2. what are Features basis of classification of viruses?
    • genetic material
    • kind of cells they attack
    • size
    • nature of their capsule coat
    • shapes
    • presence or absence of envelopes
  3. Describe the genetic material of viruses
    • Genome may be linear and composed of several strands, or a single circular molecule
    • viruses can have dsDNA (herpes, chickenpox), ssDNA dsRNA, ssRNA
    • ssDNA and dsDNA do not exist in cells
  4. Compare viral genome with bacterial genome on basis of size
    • Genome may be linear and composed of several strands, or single circular molecules
    • viral genome are much smaller than bacteria
  5. what was the first virus discovered?
    tobacco Mosaic virus
  6. Describe the host of viruses
    Most viruses infect only 1 particular host
  7. what determines attachment, specificity?
    • infect only one particular host cell
    • •Due to precise affinity of viral surface proteins or glycoproteins for complementary molecules on the
    • host
  8. what is a bacteriophage (phage)?
    virus that infects bacteria
  9. how big are viruses compared to bacteria, RBC?
    • bacteria: smaller 1000nm X 3000nm
    • RBC 10,000nm
  10. what is the capsid?
    protein coat made of protein subunits called capsomeres
  11. describe the 3 common shapes of viruses based on the capsid
    • capsomeres in a spiral formation that form
    • a tube around the nucleic acid
  12. describe the 3 common shapes of viruses based on the capsid
    • common types is icosahedron
    • 20 sides
  13. describe the 3 common shapes of viruses based on the capsid
    • many diff. shapes
    • Bacteriophages have icosahedral head and helical tail
    • Smallpox virus has several covering layers no identifiable capsid
  14. Describe the viral envelope
    • no cell membrane
    • no enveloped= naked virus
    • Some viruses -particularly animal
    • viruses have envelopes similar in composition to a cytoplasmic membrane around
    • capsid  = enveloped viruses
  15. Compare viruses with cells
  16. Describe stages of lytic replication of bacteriophages
    • Cannot replicate on their own
    • Dependent on host cell machinery
    • Replication usually results in celllysis and death
    • Lytic replication cycle
    • 5 stages
    • 1.Attachment
    • 2.Entry  
    • 4. Assembly
    • 3.Synthesis
    • 5. Release
  17. Describe lysogeny of bacteriophages
    • variation that some viruses do
    • virion attaches
    • DNA enters cell but host DNA not destroyed
  18. Compare replication of bacteriophages with animal viruses
    • Synthesis of animal viruses
    • •Depends on type
    • of nucleic acid
    • Retroviruses
    • - ssRNA
    • genome
    • •Uses reverse transcriptase
    • to make DNA from the RNA
    • •DNA serves as template to make more
    • viral RNA and proteins
    • •HIV is a retrovirus
  19. Describe entry, synthesis,and release of animal viruses
    • Still 5 basic steps – attachment,
    • entry, synthesis, assembly, release
    • •But usually have envelopes
    • Attachment –viral protein attaches to
    • receptor on host cell surface
    • Entry
    • •Naked viruses – direct penetration
    • •Enveloped viruses enter by                        membrane fusion or endocytosis
  20. What is the biggest challenge of treating viruses?
    Because viral replication uses cellular structures and pathways for growth and maintenance of healthy cells, any strategy for the treatment of viral diseases that involves disrupting viral replication may disrupt normal cellular processes as well
  21. What is the role of viruses in cancer?
    • Under normal conditions, division of cells is under strict genetic control
    • •Some genes for cell division are turned off permanently
    • •Or genes that inhibit cell division are turned on
    • •Or a combination may occur
    • Uncontrolled cell division produces a tumor
  22. what are protooncogenes?
    • genes that control cell division
    • •If these are turned on or not repressed, get uncontrolled growth
  23. What are prions?
    • powerful protein
    • normal prion
    • •Proteinaceous infectious agent
    • Discovered in 1982 by Stanley Prusiner
    • All mammals make a protein called PrP.
    • Protein can fold two ways
    • •Normal, cellular PrP
    • •Abnormal, Prion PrP
    • •Prion PrPconverts                                                  cellular PrP into                                                    abnormal form
  24. How do prions cause disease?
    • •Prion PrP converts cellular PrP into
    • abnormal form
    • As new protein is being made the prion PrP
    • causes new molecules to refold into prion form
  25. What are some examples of prion diseases
    • scrapie in sheep
    • chronic wasting disease of elk and deer
    • creutzifeld- jakob disease in humans
  26. How are prions destroyed?
    • incineration or autoclaving in 1N NaOH
    • EU made enzyme called Pnonzyme that removes prions from medical equipment
    • no treatment
  27. Viruses that have an intracellular and extracellular state "outside"
    • a-helical
    • b-polyhedral
    • c-complex small pox
    • d-complex rabbies
  28. Describe stages of lytic replication of bacteriophages
    1. Attachment?
    • •Attack results from a random collision
    • •Depends on precise fit between attachment proteins of virion
    • and receptor proteins on surface of host
  29. Describe stages of lytic replication of bacteriophages
    2. Entry?
    • •Genome moves through tube into bacterium
    • •Empty capsid is left on outside
  30. Describe stages of lytic replication of bacteriophages
    3. Synthesis?
    • •Viral enzymes degrade bacterial DNA
    • •Synthesis of viral proteins – viral structures and viral enzymes
  31. Describe stages of lytic replication of bacteriophages
    4. Assembly?
    •viral particles self-assemble inside host cell
  32. Describe stages of lytic replication of bacteriophages
    5. Release?
  33. induction?
    prophage may later be excised from chromosome