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1. The expression of genes is regulated in S. pneumoniae positive and negative regulators that respond...

1. The expression of genes is regulated in S. pneumoniae positive and negative regulators that respond to signals from the environment.

a. How can the presence or absence of glucose change the expression of the lac operon?

b. How can the presence or absence of lactose change the expression of the lac operon?

c. How could the presence of absence of tryptophan change expression of the trp operon?

d. How could the presence of absence of chorismate change expression of the trp operon?

e. If a medium contained both chorismate and tryptophan, how would the expression of the trp operon change, if at all?

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Answer #1

a) When glucose is absent ,cyclic AMP combines with catabolic activator protein and binds to the promoter region of Lac operon facilitating transcription of lac operon. But when glucose is present repressor molecule binds to operator region of lac operon and prevents transcription of lac operon.

b)When lactose is present ,repressor gets released from operator region (by binding of allolactose) and RNA polymerase transcribes lac operon.When lactose is present ,repressor binds tightly to the operator region of lac operon,preventing RNA polymerase from transcribing lac operon.

c)tryptophan operon is repressed in presence of tryptophan and expressed when tryptophan levels are low.When repressor binds to tryptophan ,it blocks expression of operon.

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