Expression Regulation

Question 1

Lac operon in proks

Answer 1

inducible operon =effector binds to induce expression
lactose binds to repressor –> lactose-repressor complex releases from operator –> transcription of lac operon

Question 2

how is the lac operon both positively and negatively controlled

Answer 2

positively controlled - binding of CAP-cAMP enhances transcription
negatively controlled - binding of lac repressor inhibits transcription

Question 3

when is the lac operon most greatly expressed?

Answer 3

when lactose levels are high (releases lac repressor) and glucose are low (CAP-cAMP binds)

Question 4

glucose inhibits transcription of the lac operon by

Answer 4

reducing levels of intracellular cAMP

Question 5

What happens to the lacI gene if lactose is not available?

Answer 5

there is no change to lacI gene expression (LacI = repressor)

Question 6

Trp operon in proks

Answer 6

repressible operon = effector binds to repressor to repress expression
tryptophan binds to repressor –> tryptophan-repressor complex binds to operator –> blocks transcription of trp operon
—> want low tryptophan

Question 7

the trp repressor blocks transcription of the trp operon when the repressor

Answer 7

binds to tryptophan

Question 8

what does tryptophan acts as in the trp operon

Answer 8

co-repressor

Question 9

attenuation of the trp operon

Answer 9

prevents completion of transcription when tryptophan levels are high (ribosome stalls and allows formation of 3/4 which is a termination signal

Question 10

location and function of enhancers in euks

Question 11

location and function of silencers in euks

Question 12

positive regulatory elements and role

Question 13

negative regulatory elements and role

Question 14

benefits of regulating at early stages of expression

Question 15

benefits of regulating at late stages of expression