Question) a) How does an Hfr strain of E. coli transfers chromosomal DNA to an F
ID: 271688 • Letter: Q
Question
Question)
a) How does an Hfr strain of E. coli transfers chromosomal DNA to an F- strain? What determines how much of the chromosomal DNA is transferred?
b)
Describe why there was growth or no growth in the conjugation minimal medium in the table below. Relate this their antibiotic resistance/sensitivity and their requirement for the amino acids Leucine, Threonine and Thiamine in order to grow.
Culture
Conjugation Minimal Medium
(+ Streptomycin)
E.coli 10-1, F-
E.coli 10-1, Hfr
E.coli 10-1, F- + Hfr
E.coli 10-2, F- + Hfr
E.coli 10-3, F- + Hfr
c) Define generalized and specialised transduction
Culture
Conjugation Minimal Medium
(+ Streptomycin)
E.coli 10-1, F-
E.coli 10-1, Hfr
E.coli 10-1, F- + Hfr
E.coli 10-2, F- + Hfr
E.coli 10-3, F- + Hfr
Explanation / Answer
1.
The Hfr cell transfers a portion of its bacterial genome to the F cell. The F factor in the Hfr cells are capable of initiating conjugative transfer. Through the mating bridge, the Hfr cells attempt to transfer most of the DNA to the other cell. The F part’s inherent factors drags all the DNA to the other cell.
The mating bridge and the contact time determines the amount of the transfer. However, the large size of the cell and inability to keep contact makes the entire genome transfer impossible.
3.
Generalized transduction is the gene transfer method from on bacterial cell to another. The bacteriophage infects the host and cause fragmentation of the genome into smaller fragments.
In specialized transduction, the viral genome is integrated into the bacterial genome and incorrect excision leads to formation of recombinants. The recombinant genome is transferred to bacterial cells and this recombination makes the specialized and generalized transduction differ from each other.
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