preQ: Under which conditions will E. coli cells express (transcribe and translate) lots of beta-galactosidase?

A) In medium with glucose as the only sugar

B) In medium with glucose and lactose

C) In medium with lactose as the only sugar

D) In medium with galactose

E) All of the above

preQ: If the repressor gene is mutated, so that no repressor protein is made, then

a) The lac operon will never be induced

b) The lac operon will always be induced

c) The lac operon will be induced whenever lactose is present

d) The lac operon will be induced whenever glucose is absent

e) The lac operon will be induced only when both lactose and glucose are present

preQ: What causes induction of the lac operon?

A) When repressor binds to the operator, regardless of CAP

B) When CAP binds to the promoter, regardless of Repressor

C) When Repressor binds to inducer

D) When both A) and B) occur

E) When CAP binds to the promoter and Repressor is not bound to the operator

preQ: In wild-type E. coli cells in medium with glucose, and no lactose:

A. CAP binds to promoter

B. Repressor binds to operator

C. Both CAP and Repressor bind to promoter and operator, respectively

D. Neither bind

preQ: If a mutation eliminates binding of inducer to the repressor, but the repressor still binds to DNA;

A) The lac operon will be always induced

B) The lac operon will never be induced

C) The lac operon will be induced whenever glucose is absent, regardless of the presence or absence of lactose

D) The lac operon will be induced only when both glucose and lactose are present

E) The lac operon will be induced only when glucose is present and lactose is absent

Lac operon demonstration

• Need volunteers for– RNA polymerase– Repressor protein– CAP protein

postQ: Under which conditions will E. coli cells express (transcribe and translate) lots of beta-galactosidase?

A) In medium with glucose as the only sugar

B) In medium with glucose and lactose

C) In medium with lactose as the only sugar

D) In medium with galactose

E) All of the above

postQ: If the repressor gene is mutated, so that no repressor protein is made, then

a) The lac operon will never be induced

b) The lac operon will always be induced

c) The lac operon will be induced whenever lactose is present

d) The lac operon will be induced whenever glucose is absent

e) The lac operon will be induced only when both lactose and glucose are present

postQ: What causes induction of the lac operon?

A) When repressor binds to the operator, regardless of CAP

B) When CAP binds to the promoter, regardless of Repressor

C) When Repressor binds to inducer

D) When both A) and B) occur

E) When CAP binds to the promoter and Repressor is not bound to the operator

postQ: In wild-type E. coli cells in medium with glucose, and no lactose:

A. CAP binds to promoter

B. Repressor binds to operator

C. Both CAP and Repressor bind to promoter and operator, respectively

D. Neither bind

postQ: If a mutation eliminates binding of inducer to the repressor, but the repressor still binds to DNA;

A) The lac operon will be always induced

B) The lac operon will never be induced

C) The lac operon will be induced whenever glucose is absent, regardless of the presence or absence of lactose

D) The lac operon will be induced only when both glucose and lactose are present

E) The lac operon will be induced only when glucose is present and lactose is absent