Question

1.)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

2.)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

3.)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

4.)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. Option A. Slow down the isomerization of lactose.

Option D recessive to wild type

Permease enzyme is secreted in the presence of Inducer I. Permease converts lactose to allolactose. If lacI is absent lacZ and lacY will not be transcribed. Hence permease will not be secreted.

If a wild type lac I isiintroduced, lac Z and Y will be synthesized only in the presence of lactose

3. Option C prevent lacS superrepressor mutations from making the lac operon uninducible

In this case, the repressor may bind to DNA but will not respond to inducer. Hence synthesis will continue all time. Tge operon is always on.