tIn the following experiment, a prototrophiv Hfr strain is mated with an auxotro
ID: 205368 • Letter: T
Question
tIn the following experiment, a prototrophiv Hfr strain is mated with an auxotrophic F- strain. The Hfr strain is str-s (streptomycin sensitive) and the F- strain is str-r (streptomycin resistant) met-, leu-, cys-.Cells are then grown on plates containing minimal media with streptomycin, methionine, and cysteine added.'
Mating: Hfr str-s, met+, cys+, leu+ X F- str-r, met-, cys-, leu-
The following growth was observed:
Why were no colonies observed after plating culture A?
Why were no colonies observed after plating culture C?
Why were cells able to grow after plating culture B?
I understand that this has to do with complementation, but I dont understand the specifics. Can you explain?
Cultures Growth A) Hfr cells only no colonies B) Hfr + F- cells 375 colonies C) F- cells only no coloniesExplanation / Answer
Culture A is Hfr cells only. These Hfr cells are streptomycin sensitive. When these cells are grown on a minimal medium plate containing streptomycin they cannot grow and form colonies as they are sensitive to streptomycin. This is the reason why no colonies were observed after plating culture A.
Culture C is F- cells only. These cells are auxotrophic and they cannot synthesize methionine, cysteine, and leucine amino acids. In order to grow these F- cells all these three amino acids should be supplied in the medium. When these cells are plated on a minimal medium plate containing streptomycin, methionine, and cysteine they cannot grow and form colonies as leucine amino acid that is required for their growth is not added to the medium. This is the reason why no colonies were observed after plating culture C.
When Hfr cells and F- cells are mated the genetic information gets transferred from the Hfr cell to the F- cell. After mating the F- cell will no longer be auxotrophic as it received the genetic information required for the synthesis of the amino acids methionine, cysteine, and leucine from the Hfr cell. So when these cells are plated on a minimal medium plate containing streptomycin, methionine, and cysteine the cells grow and form colonies on the plate. This is the reason why colonies were observed after plating culture B.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.