L5 - The lac operon 3

Question 1

what is ‘cis’ regulation?

Answer 1

(cis = on same side)
a cis-acting mutation only affects expression of a gene or operon that is in the SAME DNA molecule, regulatory sequence must be attached to target gene or operon

Question 2

what is ‘trans’ regulation?

Answer 2

(trans = on different sides)
a trans-acting mutation can affect expression of a gene or operon that is in a DIFFERENT DNA molecule, regulatory sequence doesn’t need to be attached to target gene or operon

Question 3

which regulatory state does operator act in?

Answer 3

operator acts in CIS: therefore operator only affects the operon it is attached to.
(i+, o(c), z+ / i+, o+, z-) B-galactosidase production is constitutive
(i+, o(c), z- / i+, o+, z+) B-galactosidase production is inducible

Question 4

which regulatory state does repressor act in?

Answer 4

repressor acts in TRANS: the repressor gene product can control an operon in a different DNA molecule (the repressor is a diffusible molecule)
(i+, o-, z- / i-, o+, z+) B-galactosidase production is inducible

Question 5

summary of regulation by (allo)lactose

Answer 5

1. lac operon genes required for metabolism of lactose by E.coli only transcribed when lactose present
2. in absence of lactose, the tetrameric lac repressor binds to DNA of lac operon at 2 sites: O1 and O2/O3
3. in the PRESENCE of lactose, allolactose binds to Lac repressor and causes conformational change. Hinge region disfigured and subunits don’t bind cooperatively to operator

Question 6

how does regulation by glucose occur?

Answer 6

via cyclic AMP (cAMP), glucose controls cAMP concentration

Question 7

when glucose is present is the cAMP concentration high or low?

Answer 7

glucose present = cAMP conc LOW

Question 8

when there is no glucose present is the cAMP concentration high or low?

Answer 8

cAMP conc high, enzyme Adenylate cyclase is also activated

Question 9

what is CAP?

Answer 9

catabolite activator protein (CAP) is a dimer that cAMP binds to form cAMP-CAP (this activates transcription)

Question 10

in the absence of cAMP what happens to CAP?

Answer 10

catabolite activator protein is INACTIVE