8) Consider a population of E. coli mutants that have a defect in their lacl gen
ID: 274284 • Letter: 8
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8) Consider a population of E. coli mutants that have a defect in their lacl gene, resulting in the production of a repressor protein that binds to the operator of the lac operon, but does not bind to lactose itself. If you placed these cells in a growth media containing lactose, what would happen? A) Transcription of the lac operon would only occur in the absence of lactose. B) Transcription of the lac operon would occur only in the presence of lactose. C) Transcription of the lac operon would occur normally D) Transcription of the lac operon would not occur 9) You are studying a species of bacteria that produces a lovely purple pigment, making the colonies a bright purple color when grown on a Petri dish. You are interested in finding the gene responsible for this color production. You transform a culture with a plasmid containing a transposon and an ampicillin resistance gene (bla). Realizing your transformation efficiency will be low, how might you identify bacteria that have been successfully transformed? A) Identify colonies that are not purple. B) Grow them on media containing streptomycin. C) Grow the bacteria on a plate containing ampicillin. D) Incubate them at different temperatures. E) Look for colonies that are purple. 10) Following from the previous question about purple-pigmented bacteria, assume you have successfully isolated your transformed mutants. You grow them up in culcture and spread them on the surface of multiple TSA plates. Following incubation, you observe mostly purple colonies along with an occasional clearish/white colony. What might best explain the presence of these clearish/white colonies? A) The medium lacks nutrients necessary for production of the purple pigment. B) The transposon from your plasmid has inserted itself into the middle of a gene coding for production of the purple pigment, making it defective. C) The bacterial RNA polymerase is unable to transcribe the information on the plasmicd. D) The bacterial transposon has inserted itself in the middle of the gene for RNA polymerase, preventing transcription. E) The TSA is inhibiting production of the purple pigment.Explanation / Answer
8) D) Transcription of the lac operon would not occur. Under normal condition, when lactose is absent, repressor binds to lac promoter and prevents transcription of the genes. When lactose is present, lactose binds with the repressor and inactivates it, in turn, transcription is started since repressor is not available to bind at promoter. In given condition, repressor is mutated so that it is neutral to lactose however it can bind to operator preventing transcription. Since repressor will remain bound to the operator irrespective of presence/absence of lactose, transcription will not occur.
9) C) Grow the bacteria on a plate containing ampicillin. Transformation is the transfer of DNA into the bacterial cell. We are introducing a transposon with ampicillin resistance gene, so all the transformed cells will be able to survive in a medium containing ampicillin. The purple color is not necessarily always formed.
10) B) The transposon from your plasmid has inserted....
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