In terms of lac operon regulation, what happens when E. coli is grown in medium

Question

In terms of lac operon regulation, what happens when E. coli is grown in medium containing both glucose and lactose? A. Both CAP and the lac repressor are bound to the DNA. B. CAP is bound to the DNA but the lac repressor is not. C. Lac repressor is bound to the DNA but CAP is not. D. Neither CAP nor the lac repressor are bound to the DNA. E. All of the above or None of the above B. Where would you most likely find chromatin in the beads on a string conformation? A. Heterochromatin B. Actively transcribed chromatin C. Silenced chromatin D. Deacetylated chromatin E. 30 nm fiber chromatin

Explanation / Answer

A)

When both the glucose and lactose are present in the medium, E. coli grows faster utilizing glucose first. The lactose is not utilized as the lac repressor is bound to the DNA. When available glucose is very low or absent then adenyl cyclase produces high levels of cAMP that binds to catabolite activator protein (CAP) and both cAMP and CAP bind to DNA activating transcription of lac operon. Therefore, option C is correct.

B)

The histone proteins are wrapped around DNA in a nucleosome which is atively transcribed. This DNA encoding genes is loosely packed and is associated with RNA polymerase, so that , it is readily transcribed. This DNA is found in euchromatin. Therefore, option B is correct.

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