lec 27 transcription cont.

Question 1

all genes on an operon are transcribed onto what?

Answer 1

a single mRNA

Question 2

lac operons consist of

Answer 2

a repressor, promoter, operator, and structural genes (lacZ, lacY, etc.)

Question 3

in negative regulation, what happens to the lac operon when lactose is not present/present?

Answer 3

when lactose is not present, the lacI attaches to the operator to stop transcription. When lactose is present, the allolactose inducer attaches to the repressor to prevent it from attaching to the operator, allowing transcription

Question 4

when glucose is low, and positive regulation is occurring what happens?

Answer 4

cAMP is made in low glucose and it attaches to CAP to form the CAP-cAMP complex which binds to the promoter, resulting in enhanced transcription

Question 5

what happens when lactose and glucose are present?

Answer 5

cAMP cannot be made so it cannot help in transcription and due to glucose being present, very small amounts of transcription using lactose occurs

Question 6

what does the trp on the trp operon do?

Answer 6

it acts as a co-repressor

Question 7

what happens when trp is low?

Answer 7

the transcription will occur because low trp means it cannot bind to the repressor

Question 8

what happens when trp is high?

Answer 8

the transcription will be repressed by trp binding to the repressor