Question

1.)A.)The lac operon is inducible by the presence of lactose. Loss-of-function mutations in the lacI gene, which encodes the lac repressor (pick all that apply):

A.)slow down the isomerization of lactose into allolactose
B.)decrease the amount of permease activity in the cell in the presence of lactose.
C.)prevent loss-of-function lacZ mutations from making the lac operon uninducible
D.)are recessive to wild type

B.)Mutations that eliminate the lacO operator site (pick all that apply):

A.)slow down the isomerization of lactose into allolactose
B.)decrease the amount of beta-galactosidase in the cell in the presence of lactose
C.)prevent lacS superrepressor mutations from making the lac operon uninducible
D.)are recessive to wild type

C.)Loss-of-function mutations in the lacZ gene, which encodes beta-galactosidase (pick all that apply):

A.)slow down the isomerization of lactose into allolactose
B.)decrease the amount of permease activity in the cell in the presence of lactose
C.)prevent lac repressor from binding the lacO operator site
D.)prevent IPTG from inducing the lac operon

D.)You are studying the Tory operon, which encodes the TorA and TorB genes, and is normally inducible by Torose. You find a mutation, m1, that causes the Tory operon to be uninducible. You examine the merodiploid (m1 TorA+ TorB-)/(+ ToryA- TorB+) and find that Tor A is uninducible and TorB is inducible. You conclude that:

A.)m1 acts in cis
B.)m1 acts in trans

Answer 1

1) Lac I gene is responsible for making the repressor protein that sits on the lacO site and inhibit the transcription.

So option A is wrong that it will not slow down the isomerization. B is also wrong because it has nothing to do with permease activity.

C is also wrong.

The correct answer is option D that is it is recessive to wild type.

2) LacO site has nothing to do with lactose isomerization and and amount of beta galactosidase. So, option A and B are wrong.  

Option C is correct option because if the lac O is mutated then the lacS won't be able to attach to the site and lacS super repression will not be there.

Option D is also correct as it is recessive mutation in wild type.

3) The only correct answer is A that is it will slow down the isomerization of lactose into allolactose.

All other options are wrong.

4) The correct answer is option A that is M1 acts in cis because if it would have been acting trans then the TorB would not be induced in merodiploid.