BMSC 210 Last 3 Lectures before Midterm 2

  1. Mechanisms to diminish viral infections
    • -RNA interference, CRISPR
    • -restriction modification system
  2. Restriction Modification System
    • -only works against double stranded DNA viruses 
    • -RE's cleave DNA 
    • -modification of host DNA protects its own DNA
  3. How Viruses evade bacterial restriction systems
    • -chemical modification of viral DNA (glycosylation or methylation)
    • -proteins that inhibit RE system
  4. Most viruses are?
  5. Viral Metagenome
    • -sum total of all viral genes in an environment
    • -most yet to be discovered
  6. Baltimore Classification of Viruses
    • -7 classes of viruses 
    • -1975 nobel prize
  7. Positive strand RNA virus
    -single stranded RNA genome with SAME orientation as its mRNA
  8. Negative strand RNA virus
    -single stranded RNA genome with orientation COMPLEMENTARY to its mRNA
  9. ____ bacteriophage genomes are the simplest?
  10. Influenza
    • -enveloped
    • -polymorphic virus
    • -segmented genome (8 segments)
  11. Hemagglutinin
    • -found as spikes on influenza virus
    • -cause clumping of RBC
  12. How can influenza elude immune system?
    • -antigenic shift
    • -antigenic drift
  13. Antigenic shift
    • -portions of RNA from two distinct strains infect the same cell and are reassorted 
    • -generates virions with unique surface proteins
    • -produces pandemics
  14. Antigenic shift
    -structures of neuraminidase and hemagglutinin proteins are subtly altered
  15. Retroviruses
    • -animal viruses that cause certain cancers and immunodeficiency syndrome (AIDS)
    • -class VI viruses
    • -require reverse transcriptase
  16. Hep B virus
    • -class VII virus (ds DNA)
    • -replicates through RNA intermediate
    • -has reverse transcriptase
  17. Bacterial Viruses
    • -diverse
    • -best studied infect enteric bacteria
    • -most have dsDNA genomes
    • -most naked, some lipid envelopes
    • -complex structures
  18. Bacteriophage life cycle
    • -virulent mode
    • -temperate mode
  19. Virulent mode
    -viruses lyse host cells after infection
  20. Temperate Mode
    • -viruses replicate their genomes in tandem with host genome without killing host
    • -virus can also be lytic
  21. Bacteriophage T4
    • -linear dsDNA genome
    • -infects E. coli
    • -virulent life cycle
    • -DNA contains 5-hydroxymethylcytosine (resistant to all known RE)
  22. Early and Middle Proteins
    -enzymes needed for DNA replication and transcription
  23. Late Proteins
    -head and tail proteins and enzymes required to liberate mature phage particles
  24. Temperate phage
    -can undergo stable genetic relationship within the host
  25. Lysogeny
    -state where most virus genes are not expressed and virus genome is replicated in synchrony with host chromosome
  26. Lysogen
    -bacterium containing a prophage
  27. Lambda virus
    • -linear dsDNA genome
    • -complementary single stranded regions 12 nucleotides long at the 5' terminus of each strand 
    • -upon cell penetration DNA ends base pair, creating COS site, where DNA ligates and forms double stranded circle
  28. Animal Viruses
    • -entire virion enters cell (unlike prokaryotes)
    • -contain all known modes of viral genome replication
    • -many can be enveloped (as virus leaves host cell it steals part of host cell lipid bilayer)
  29. Retroviruses
    • -RNA viruses that replicate through DNA intermediate
    • -enveloped
    • -contain reverse transcriptase, integrase and protease 
    • -contain specific tRNA
  30. Retroviral genome
    • -unique
    • -two identical ssRNA molecules in + orientation
    • -contains specific genes gag, pol, env
  31. gag
    -encodes structural proteins in retroviral genome
  32. pol
    -encodes reverse transcriptase and integrase in retroviral genome
  33. env
    -encodes envelope proteins in retroviral genome
  34. Defective viruses
    -require other virus (helper virus) to provide some function
  35. satellite viruses
    -defective viruses for which no intact version exists, rely on unrelated viruses as helpers
  36. viroids
    • -infectious RNA that lack protein coat
    • -smallest known pathogens
    • -cause important plant diseases
    • -small circular ssRNA genomes
    • -do not encode any proteins
  37. Prions
    • -infectious proteins whose extracellular form contains no nucleic acids
    • -misfolding results in neurological symptoms
  38. Infectious prion
    -pathogenic form transmitted between animals or humans
  39. sporadic prion
    -random misfolding of a normal healthy prion protein in uninfected individual
  40. inherited prion
    -mutation in prion gene yields misfolded protein more often
  41. How old is the earth?
    -4.5 billion years
  42. Stromatolites
    • -microbial mats with layers of filamentous prokaryotes
    • -3.5 billion years old
    • -used to be anoygenix filamentous, now oxygenic cyanobacteria
  43. Surface origin hypothesis
    • -formed in inorganic compounds in ponds on surface
    • -temp changes, meteor impacts, dust clouds and storms argue against it
  44. Subsurface origin hypothesis
    • -started in thermal springs on ocean floor
    • -more stable conditions
    • -H2 and H2S for energy supply
  45. Early earth was _____ therefore primitive cells were ______ and likely _______
    • anoxic
    • anaerobic
    • chemolithotropic
  46. When did bacteria and archaea diverge
    -4 billion years ago
  47. Banded Iron Formations
    -laminated sedimentary rocks, prominent features in geological record
  48. Oldest eukaryotic microfossils
    -2 billion years old
  49. Transfection
    -transformation of bacteria with DNA extracted from a bacterial virus
  50. Competent
    -cells capable of taking up DNA and being transformed
  51. Electroporation
    -method where electricity is used to force cells to take up DNA (competency)
  52. Transduction
    -transfer of DNA from one cell to another by a bacteriophage
  53. Generalized vs Specialized transduction
    • -general is any portion of host genome packaged into virion
    • -specialized specific region of host chromosome is integrated in virus genome
Card Set
BMSC 210 Last 3 Lectures before Midterm 2
BMSC 210 Last 3 Lectures before Midterm 2