Question

1) The lac operon is…

a) Positive repressible

b) Both negative inducible and positive repressible

c) Positive inducible

d) Negative inducible

2) An activator regulatory protein…

a) Is involved in negative regulatory control

b) Is a cis acting regulatory element

c) Recruits RNA polymerase to the promoter

d) Prevents RNA polymerase from binding the promoter

3) For the lac operon, the presence of the substrate (lactose) activates the repressor. True or False?

a) true

b) false

4) cAMP…

a) Activates catabolite activator protein (CAP)

b) Deactivates the repressor

c) Activates the repressor

d) Activates RNA Polymerase

5) For the lac operon, when glucose is absent and lactose is absent

a) There is reduced transcription of the structural genes

b) There is enhanced transcription of the structural genes

c) None of the above

d) Transcription is turned off

6) For the lac operon, when glucose is present and lactose is present

a) None of the options

b) cAMP-CAP is bound to the promoter and the repressor is bound to the operator

c) cAMP-CAP is not bound to the promoter and the repressor is not bound to the operator

d) cAMP-CAP is bound to the operator and the repressor is bound to the promoter

Answer 1

1) negative inducible means the operon is normally repressed in the cell by a repressor protein binding to the operon, and the expression of the operon is induced by an inducer which prevents the binding of the repressor to the operator. the lac operon is repressed normally in the cell by the repressor protein binding to the operator, in the presence of an inducer, the repressor is inactivated so the lac operon is expressed that is lac operon is negative inducible

positive repressible means operon is expressed always and an activator protein binds to the operon always  and when and in the presence of a regulatory molecule it binds to the activator and inactivates it so that activator cannot bind to the DNA so the operon is not transcribed, such a regulation is not found in the lac operon.

positive inducible means the activator is not normally bound to the operon, but in the presence of a regulatory molecule the activator binds to the regulatory molecule so it can bind to the operon and activate the expression of operon, CAP protein binds to the operon and induces the expression of operon when bound with cAMP , CAP protein activates the expression of lac operon so the lac operon is positive inducible.

so the answers are negative inducible, positive inducible.