Use the following choices to answer the question:
a. Catabolite repression
b. DNA polymerase
c. Induction
d. Repression
e. Translation


Mechanism by which the presence of glucose inhibits the lac operon.

Verified step by step guidance

1. Identify the key concept in the question: it asks for the mechanism by which glucose presence inhibits the lac operon.
2. Recall that the lac operon is a set of genes involved in lactose metabolism, and its expression is regulated depending on the availability of glucose and lactose.
3. Understand that when glucose is present, the cell prefers to use it over lactose, so it suppresses the lac operon to conserve energy.
4. Recognize that this suppression mechanism is called catabolite repression, where glucose presence leads to decreased levels of cyclic AMP (cAMP), reducing activation of the lac operon.
5. Match the correct term from the given choices to this mechanism, which is 'catabolite repression'.

Key Concepts

Catabolite Repression

Catabolite repression is a regulatory mechanism in bacteria where the presence of a preferred carbon source, like glucose, inhibits the expression of genes involved in the metabolism of alternative sugars. In the lac operon, glucose lowers cAMP levels, preventing activation of the CAP protein, thus repressing lac operon transcription.

Lac Operon Regulation

The lac operon controls the metabolism of lactose in E. coli and is regulated by both induction and repression mechanisms. When glucose is absent and lactose is present, the operon is induced to produce enzymes for lactose utilization; glucose presence inhibits this process through catabolite repression.

cAMP and CAP Protein Interaction

Cyclic AMP (cAMP) binds to the catabolite activator protein (CAP) to form a complex that enhances RNA polymerase binding to the lac operon promoter. Glucose reduces intracellular cAMP levels, preventing CAP binding and thus inhibiting transcription of the lac operon.