CBG Lecture 18: Bacterial Conjugation

Question 1

what experiment showed that physical contact is needed between bacteria to allow conjugation

Answer 1

U tube with filter small enough to block bacteria going through
no conjugation/gene transfer happened

Question 2

why is the transfer of genetic material not reciprocal

Answer 2

as it occurs only in one direction

one cell acts as donor, other recipient

Question 3

what is donor ability imposed by

Answer 3

its a hereditary state imposed by a fertility factor (F)

Question 4

what is F

Answer 4

a fertility factors

Question 5

which is recipient, F+ or F-

Answer 5

F- is recipient

F+ is donor

Question 6

how is the F factor transmitted

Answer 6

during physical contact or conjugaion

Question 7

what does the F plasmid do

Answer 7

directs the synthesis of pilli which initiate contact with a recipient and draw it closer, allowing the F DNA to pass through a pore into the recipient cell

Question 8

what happens during conjugation

Answer 8

the pilus pulls 2 bacteria together
then a bridge (essentially a pore) forms between the two cells then one stran dof plasmid DNA passes into the recipient bacterium and each single strand becomes dbl again

Question 9

how do HFr cells arise

Answer 9

result from the intrgration of the F factor into the chromosome as opposed to the plasmid

Question 10

what does HFr stand for

Answer 10

high frequency (indicates a high frequency of recombination)

Question 11

what happens during conjugation between HFr and F=

Answer 11

a part of the chromosome is transferred with F and random breakage interrupts the transfer before the entire chromosome is transferred

Question 12

in conjugation between HFr and F-, what happens after random breakage interrupts the transfer of chromosmoe

Answer 12

the chromosomal fragment can the recombine with the reipient chromosome

Question 13

what is interrupted mating

Answer 13

crossing Hfr str(s)wildtype with F- str(r) mutant then put into kitchen blender to disrupt mating cell pairs, then plated onto a medium containing streptomycin to kill Hfr

Question 14

in which strains does every cell donate chromosomal alleles during F transfer

Answer 14

Hfr cells

Question 15

why is the frequency of recombinance for HFr cells greater than F cells

Answer 15

because F factor is integrated into chromosome and evey cell donates chromosomal alleles during F transfer

Question 16

which type of bacterial strains are used for genetic mapping? why

Answer 16

Hfr strains because they transfer chromosomal markers efficiently

Question 17

what is an F’ f prime cell

Answer 17

when the integrated F factor leaves the chromosome of an Hfr cell and moves back into the cytoplasm and in some rare cases carries a few host chromosomal genes with it

Question 18

which cells are involved in mapping by interrupted conjugation

Answer 18

Hfr and F=

Question 19

what are exoconjugants

Answer 19

the remaining f- cells after the Hfr cells have been killed after interrupted conjugation

Question 20

define auxotrophic

Answer 20

cant synthesise aas themselves

Question 21

what is fertility factor F

Answer 21

an episome

Question 22

what is an episome

Answer 22

plasmid which can either be free in the cytoplasm or integrated into the bac chromosome

Question 23

where does transfer between Hfr and F- begin

Answer 23

in the middle of F factor at oriT

Question 24

where is oriT

Answer 24

origin of transfer, in the middle of F factor

Question 25

does recombination take place between HFr and F- cells

Answer 25

not always but there must be crossing over if transfer is to be permanent

Question 26

what happens if transfer between HFr and F- cells is interrupted

Answer 26

linear DNa is broken down F- remains F-

Question 27

between HFr and F- cells does all the transferred material remain in the recipient

Answer 27

no only any parts which is invorporated into the bacterial chrom by corssing over

Question 28

what gene is responsible for the production of the sex pilus

Answer 28

tra (transfer) genes

Question 29

what is an insertion sequence of F plasmid

Answer 29

IS = insertion sequence

through these sequences the plasmid will eventually be able to insert in the chromosome by homologous recombination

Question 30

what is an F’ cell

Answer 30

bacterial chrom with F plasmid containing a few chromosomal genes

Question 31

what is Hfr cell

Answer 31

just bacterial chromosome with integrated F plasmid in bac chrom

Question 32

what is F- cell

Answer 32

just bact chrom (no F plasmid)

Question 33

what is F+ cell

Answer 33

bac chrom with F plasmid

Question 34

what does plating onto streptomycin do

Answer 34

kill HFr cells

Question 35

in 1957: Jacob and Wollman – 2 experiment, what did plating onto strp medium lacking leucine and threonine do

Answer 35

kill untransform F-, so only selects transformed F-

Question 36

which number of crossing over events will be lowest frequency

Answer 36

quadruple crossover