7) Consider an E. coli cell that has a defect in the gene that produces the cata

Question

7) Consider an E. coli cell that has a defect in the gene that produces the catabolite activator protein (CAP), ma it unable to produce this protein. This cell would king A) function normally with regards to lac operon expression B) only turn on transcription of the lac operon in the presence of lactose not turn on transcription of the lac operon regardless of levels of glucose D) only turn on transcription of the lac operon in the absence of glucose E) turn on transcription of the lac operon all the time 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 successully solated 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 polymer The bactera RNA polymerase is unable to transceribe the information on the plsmid cterial 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

7) B , Since CAP is not produced then it is no longer available to bind cAMP and therefore the cAMP-CAP complex is absent. As RNA Pol has poor affinity for DNA, trancsription will not happen at a higher rate.

8) D, Transcription of genes will not occur since repressor is unable to bind to lactose, and it will remain active and occupy the operator, thus RNA pol will not get access to promoter due to steric hindrance and the transcription will not take place.

9) C, since the plasmid contains genes for amplicillin resistance then the recombinants can be identified by growing them on ampicillin containing plates. Those which are able to survive or resistant colonies are recombinants.

10) A, or E TSA medium tryptic soya agar medium components may be inhibiting production of purple pigment.

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