Question

Compare the regulation of the lac operon and the effect on the production of ß-galactosidae when E. coli is grown under the following conditions:

a) In the presence of high levels of lactose and absence of glucose

b) In the presence of high levels of lactose and high levels of glucose

Answer 1

Solution

a) In the presence of high levels of lactose and absence of glucose

=Strong transcription of the lac operon occurs. With more production of beta galactosidase

Because The lac repressor is released from the operator because the inducer (allolactose) is present.

The cAMP levels are high because glucose is absent, so CAP is active and bound to the DNA. CAP helps RNA polymerase bind to the promoter, permitting high levels of transcription

b) In the presence of high levels of lactose and high levels of glucose

=Low-level transcription of the lac operon occurs. Low or leaky level beta galactosidase production occure.

Because The lac repressor is released from the operator because the inducer (allolactose) is present.

The cAMP levels, however, are low because glucose is present. Thus, CAP remains inactive and cannot bind to DNA.