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 cAMP receptor protein (CRP), which then enhances the transcription of the operon.
2. Consider the effect of glucose on cAMP levels: Normally, high levels of glucose inhibit the production of cAMP. Therefore, in the presence of glucose, cAMP levels are low, reducing the activity of CRP and thus decreasing the transcription of the lac operon.
3. Analyze the impact of lactose: Lactose acts as an inducer of the lac operon by binding to the repressor and preventing it from binding to the operator site. This allows RNA polymerase to transcribe the genes necessary for lactose metabolism.
4. Predict the regulation in mutant cells: In a mutant lacking adenylyl cyclase, cAMP cannot be synthesized regardless of glucose levels. This means that CRP cannot be activated, potentially altering the regulation of the lac operon.
5. Evaluate each condition: For each given condition (a-d), consider how the absence of cAMP synthesis would affect the regulation of the lac operon compared to wild-type cells, focusing on the presence or absence of lactose and glucose.

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, which prevents the synthesis of cAMP, a crucial signaling molecule.

cAMP and Adenylyl Cyclase

cAMP (cyclic adenosine monophosphate) is a secondary messenger that plays a vital role in cellular signaling. 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. In mutants lacking adenylyl cyclase, cAMP cannot be produced, disrupting this regulatory mechanism.

Catabolite Repression

Catabolite repression is a regulatory mechanism that ensures bacteria preferentially utilize the most efficient energy source. In the presence of glucose, the synthesis of cAMP is inhibited, leading to reduced activation of the lac operon, even if lactose is available. This mechanism allows cells to conserve energy by prioritizing glucose metabolism over lactose, which is less efficient. Understanding this concept is crucial for predicting how the lac operon will behave in different nutrient conditions.