Question

the model shows the lac operon found in a prokaryotic cell.
the lac operon in e. coli
what would change structure 4 so it would be unable to bind to structure 3?
a. the presence of lactose in the environment
b. the removal of the promoter gene
c. the production of enzymes for breaking down lactose
d. the binding of the lac repressor to the genes for the enzymes

Explanation:

• In the lac operon system, when lactose is present in the environment, it acts as an inducer.
• The lactose binds to the repressor (structure 4). This binding causes a conformational change in the repressor.
• As a result of this change, the repressor is unable to bind to the operator (structure 3).
• Option B: Removing the promoter gene would affect RNA polymerase binding (not the repressor - operator interaction).
• Option C: Production of enzymes is a consequence of the operon being on (after the repressor is not bound to the operator), not the cause of the repressor - operator un - binding.
• Option D: Binding of the lac repressor to the genes (operator) is the normal “off” state of the operon.

Answer:

A. The presence of lactose in the environment