microbial genetics

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  1. required steps for DNA transfer
    • 1. cell-cell contact of donor and recipient (more than just touching)
    • 2. preparing the DNA for transfer = mobilization
    • 3. DNA transfer
    • 4. reformation of circular DNA in the recipient cell
  2. the most common way to transfer DNA
  3. conjugation
    plasmids transferring DNA molecules from one cell to another
  4. self-transmissible plasmids can do steps ? and ? driving their own cell to cell transfer
    • steps 1 and 2
    • 1: tra genes enable formation of a mating pair
    • 2. oriT genes determine where on the plasmid DNA transfer is initiated
  5. self-transmissible plasmids must have a complete set of ? genes
    tra: allow the plasmids to transfer themselves into other bacteria
  6. mobilized plasmids can do step bur NOT step ?
    step 2: can be transferred by other self-transmissible elements

    step 1: canNOT transfer itself into other bacteria
  7. examples of self-transmissible plasmid
    F plasmid: can integrate itself into the bacterial chromosome by homologous recombination, mutant that always expresses the tra genes

    R plasmid: a conjugation factor that promotes resistance to agents such as antibiotics and bacteriophage
  8. what are mobilizable plasmids?
    plasmids that lack genes to initiate self transfer but DO encode the functions needed specifically for transfer of their own DNA
  9. example of mobilizable plasmids
    ColE1: inhibits other E.coli strands
  10. mobilizable plasmids must have genes
    mob: proteins nick DNA at the origin of transfer (oriT) and initiate single stranded transfer of DNA into the recipient bacterium
  11. non-transmissible plasmids canNOT
    • 1. transfer itself into other bacteria
    • 2. be transferred by other self-transmissible elements
  12. cell to cell contact is dependent upon what system?
    • mpf system (mating pair formation):
    • functions as a secretion machinery for intercellular DNA transfer during bacterial conjugation
  13. is bacteria reproduced sexually?
    NO, it reproduces asexually
  14. cell to cell contact sex pilus is produced from a single protein called ? a product of the ? gene
    Pilin, traA
  15. cell to cell contact requires a ? donor cell. produced by the F plasmid is called ?
    sex pilus, "F pilus"
  16. cell to cell contact pilus extends from donor cell and contacts recipient cell to produce the ?
    mating pair
  17. the pilus ? bringing the cells into close contact. ? and ? stabilize cell to cell interaction
    the pilus depolymerizes bringing the cells into close contact. TraN and TraG stabilize cell to cell interaction
  18. the actual structure of the "tube" through which the DNA passes is made of several ?
    tra proteins
  19. DNA trasnfer is dependent on the plasmid encoded system
    Dtr (DNA transfer and replication)
  20. the DTR sstem includes ? gene products that cause ?
    include tra, cause initiation of DNA replication, DNA trasnfer, reformation of the plasmid in the recipient cell
  21. the F plasmid has how many different origins of replication and what are they ?
    TWO: oriV (otigin of replication) & oriT (origin of transfer)
  22. oriV is used only for plasmid replication during the ? and promotes what ?
    vegetable cell cycle, bidirectional theta-form replication 
  23. oriT is used during ? and promotes ?
    conjugative plasmid transfer, looped rolling circle replication
  24. to begin "looped rolling circle replication" production of ? at oriT
    a single stranded nick
  25. looped rolling circle replication steps
    • 1. leading strand is covalently linked to parental template for the lagging strand (if double stranded)
    • 2. prior to precursor synthesis, the linear branch had a 5' terminus ("A" protein acted there)
    • 3. rolling circle continues unabated forming concatemers (dd or dd)
    • 4. circular template for leading strand synthesis never leaves the circular part of the molecule
    • 5. DNA can only be nicked to start the process IF it is supercoiled
  26. a complex of two plasmid-encodes proteins ? bind to ?
    Tral and TraY, oriT
  27. ? is called the relaxase, when it nicks at oriT, it becomes convalently attached to the ? end of DNA
    Tral, 5'
  28. a plasmid that is not self-transmissible but that is mobilizable must have only the ? system
    Dtr (DNA transfer replication)
  29. the strand the is peeled off of the rolling circle is transferred into the
    recipient cell
  30. the end is transferred into the recipient cell first
    5' end
  31. the protein, bound to the 5' end is transferred into the recipient cell an remains in the ?
    region of cell-to-cell contact
  32. the 5' end is help at the while the strand that is peeled off into the recipient
    cell fusion point
  33. strand DNA synthesis takes place in the donor cell
  34. DNA-pol (I/II/III) used the 3' end as a primer and proceeds around the plasmid until it gets back to oriT
    DNA pol III
  35. strand DNA synthesis takes place in the recipient cell
  36. ? are produced and ? are synthesized
    RNA primers, okazaki fragments
  37. when the leading strand repilcation has gone all te way around the circle:
    Tral nicks at oriT again, releasing the entire displaced strand, ligation in the donor cell by Tral regenerates a complete double stranded circle
  38. synthesis of the complementary strand
    the product of one other tra gene is a primase, it makes RNA
  39. after competed conjugation the recipient is now what?
  40. transconjugant
    carries out F plasmid replication, initiated at oriV, each time it divides, has now become a potential donor, will exhibit "surface exclusion" aka entry exclusion
  41. a cell exhibiting surface exclusion expresses the ? and ? protein on its surface
    TranS and TraT
  42. a cell exhibiting surface exclusion can/can't form mating pairs with other f-plasmids
  43. a cell exhibiting surface exclusion can/can't be a recipient of the same plasmid or any other plasmid transferred during conjugation
    CAN'T; F cells can't serve as a recipent to other F cells, but they CAN however serve as recipient to a plasmid not similar to the F plasmid
  44. a cell exhibiting surface exclusion can/can't still be a recipient for conjugation that uses a pilus constructed from a different pilin
    it CAN
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microbial genetics
2013-10-10 21:29:37

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