Control of gene expression - Lecture 10

Question 1

How do polymerases know when to transcribe a gene?

Answer 1

Due to the lac and Trp operon

Question 2

What is an operon?

Answer 2

A cluster of genes transcribed by the same promotor that gives rise to polycistronic mRNA genes usually related

Question 3

How does the lac operon work?

Answer 3

When there’s no lactose the lac operon is repressed
The repressor binds to the operator which stops RNA from clearing promotor
Allolactase binds to the repressor which dissociates from the operator

Question 4

What are cis-acting elements:?

Answer 4

Will only regulate DNA to which its directly joined
Dominant
A mutation in regulatory element

Question 5

What are trans-acting factors?

Answer 5

A mutation that alters the activity of regulatory proteins
Will regulate genes anywhere
Mostly protein transcription factors
Recessive

Question 6

What is lacO^c?

Answer 6

Mutated operator
Constitutive

Question 7

What is lacI-

Answer 7

Mutated repressor
Constitutive

Question 8

What is catabolite repression?

Answer 8

Several operons allowing the use of alternate carbon sources are repressed by glucose
They only become active when all glucose are used up
This occurs by catabolite repression

Question 9

What is the role of CRP?

Answer 9

Its required by RNA polymerase
cAMP binds to it which permits DNA binding
If there’s high glucose there’s low cAMP so the lac operon is off
If there’s low glucose there’s high cAMP so lac operon is off

Question 10

What is the Trp operon?

Answer 10

Contains genes for the synthesis of animo acid tryptophan
Trp repressor binds to operator in presence of tryptophan which prevents transcription
This means the Trp operon is repressed by tryptophan