Question

The lactose repressor regulates expression of a set of genes for lactose metabolism, which are adjacent...

The lactose repressor regulates expression of a set of genes for lactose metabolism, which are adjacent
to its binding site on the bacterial chromosome. In the absence of lactose in the medium, the binding of
the repressor turns the genes off. When lactose is added, an inducer is generated that binds to the
repressor, preventing it from binding to its DNA target, thereby turning off gene expression. Inside E. coli,
there are about 10 molecules of lactose repressor (10E-8 M) and one binding site (10E-9 M) on the bacterial
genome.
a. In the presence of lactose (or its non-metabolizable analog, IPTG), what is the ratio of lac promoter
occupied by RNA polymerase versus any of the other 3000 E. coli promoters? (P_ol-P_lac/ P_ol-P)
b. In the absence of lactose (or its non-metabolizable analog, IPTG), what is the ratio of repressor bound
Plac promoter versus RNA polymerase-bound Plac promoter (R-P_lac/ P_ol-P_lac)? Can you explain the
result?

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Answer #1

a. Answer:- 0:10

Explanation:- lac operon model in the presence of lactose:--

b. Answer :- 10:0

Explanation:- lac operon in the absence of lactose:-

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