Question

The lac operon codes for enzymes that break down lactose, but this operon is only used when needed. This includes:

1. When the repressor is bound at the operator

2.When RNA polymerase is bound to the promotor WITHOUT the CAP molecule

3.When the CAP and cAMP molecules are bound to the RNA polymerase and lactose is bound to the repressor

4.When the CAP and cAMP molecules are bound to the RNA polymerase and lactose is NOT bound to the repressor

Answer 1

Bacteria use glucose first if both glucose and lactose are present, and the enzymes required for the lactose metabolism is produced only lactose is present in the medium.

lactose is an inducer of the lac operon, expression of the lac operon is inhibited by lac repressor, lac repressor binds to the operator and prevents the movement of RNA polymerase, but lactose inhibits lac repressor, so in the presence of lactose, lac repressor cannot inhibit lac operon.

CAP is catabolite activator protein, it binds to the CAP binding site and recruits RNA polymerase to the lac promoter, CAP requires cAMP to bind to DNA if glucose is present it inhibits cAMP synthase, so levels of cAMP is low so CAP cannot bind to the DNA if glucose is present so lac operon is expressed at low levels.

so the answer is

3.When the CAP and cAMP molecules are bound to the RNA polymerase and lactose is bound to the repressor