In a mutant that lacks adenylyl cyclase, the enzyme that synthesizes cAMP, predict which of the following conditions of extracellular lactose and glucose would cause regulation of the lac operon to differ from that of wild-type cells. a. no lactose, no glucose b. no lactose, abundant glucose c. abundant lactose, no glucose d. abundant lactose, abundant glucose

Verified step by step guidance

1. Understand the role of adenylyl cyclase: Adenylyl cyclase is responsible for converting ATP to cyclic AMP (cAMP). In the context of the lac operon, cAMP binds to the catabolite activator protein (CAP), which then binds to the promoter region of the lac operon to enhance transcription when glucose levels are low.
2. Analyze the effect of no adenylyl cyclase on cAMP levels: Without adenylyl cyclase, cAMP cannot be synthesized. This means that CAP cannot be activated, leading to reduced transcription of the lac operon regardless of lactose presence when glucose is low.
3. Evaluate condition a (no lactose, no glucose): In both mutant and wild-type cells, the lac operon would be off due to the absence of lactose, the inducer. The lack of adenylyl cyclase and thus cAMP does not change the regulation under this condition.
4. Evaluate condition b (no lactose, abundant glucose): Similar to condition a, the lac operon would be off in both mutant and wild-type cells due to the absence of lactose. High glucose levels would normally inhibit lac operon activity through catabolite repression, but the absence of cAMP in the mutant does not affect this since the operon is already off.
5. Evaluate condition c (abundant lactose, no glucose): In wild-type cells, low glucose would lead to high cAMP levels, activating CAP and thus enhancing lac operon transcription. In mutant cells, the absence of cAMP means CAP cannot be activated, leading to lower expression of the lac operon despite the presence of lactose. This condition shows a difference in regulation between mutant and wild-type cells.

Key Concepts

Lac Operon Regulation

The lac operon is a set of genes in E. coli that are responsible for the metabolism of lactose. Its regulation is influenced by the presence of lactose and glucose. When lactose is present, it binds to the repressor protein, allowing transcription of the operon. Conversely, high glucose levels inhibit the operon through catabolite repression, preventing cAMP production and thus reducing the activity of the operon.

cAMP and Adenylyl Cyclase

Cyclic AMP (cAMP) is a secondary messenger important for signal transduction in cells. It is synthesized from ATP by the enzyme adenylyl cyclase. In the context of the lac operon, cAMP levels are inversely related to glucose concentration; low glucose leads to high cAMP, which activates the CAP (catabolite activator protein) to enhance transcription of the lac operon. A mutant lacking adenylyl cyclase would therefore have low cAMP levels, affecting operon regulation.

Catabolite Repression

Catabolite repression is a regulatory mechanism that ensures bacteria preferentially utilize the most efficient energy source. In the case of the lac operon, when glucose is abundant, it inhibits the expression of genes involved in lactose metabolism, even if lactose is present. This is mediated by low cAMP levels, which prevent CAP from binding to the promoter, thus reducing transcription of the lac operon genes.