L8

Question 1

Cis regulatory element:

Answer 1

Non-coding DNA sequence regulating transcription of adjacent genes

Question 2

Trans regulatory element:

Answer 2

Diffusible gene product regulating gene expression throughout the genome

Question 3

Mutations in the operator

Answer 3

O^c: change in the DNA sequence of the operator (repressor unable to bind). Leads to constitutive expression of the operon.

Question 4

Operators are cis-acting:

Answer 4

regulates the expression of all adjacent genes on the same allele.

Question 5

Mutations in gene 1 (repressor)

Answer 5

I-: change in DNA sequence of gene 1 resulting in no synthesis of the repressor, is constitutive, I+ is dom to I-

Question 6

Repressors are trans-acting:

Answer 6

can regulate all structural operon genes, whether on same DNA molecule or on a different one

Question 7

I^s

Answer 7

Change in DNA sequence of gene 1 resulting alteration of allosteric site of the repressor, cannot bind allolactose and thus constitutively inhibits the expression of the operon, even in presence of lactose

Question 8

Mutations in the promotor

Answer 8

• are cis-acting
• P- results in no expression of entire operon
• P+ is dom to P-

Question 9

Positive regulation of the lac operon

Answer 9

• Binding of the activator to the activator binding site (ABS) heightens rate of transcription
• The DNA binding site of activators is only functional when an effector binds to its allosteric site

Question 10

Mutations affecting CAP

Answer 10

CAP-: change in DNA sequences of the ABS in the operon promoter (CAP can’t bind to mutated ABS)
- trans-acting