For an E. coli strain with the lac operon genotype I⁺ P⁺ O⁺ Z⁺ Y⁺, identify the level of transcription of the operon genes in each growth medium listed. Specify transcription as 'none,' 'basal,' or 'activated' for each medium, and provide an explanation to justify your answer.

Growth medium contains lactose and glucose.

Verified step by step guidance

1. <span>Step 1: Understand the components of the lac operon. The lac operon in E. coli consists of the genes lacZ, lacY, and lacA, which are involved in lactose metabolism. The operon is regulated by the presence of lactose and glucose in the environment.</span>
2. <span>Step 2: Identify the role of the I⁺, P⁺, O⁺, Z⁺, and Y⁺ components. I⁺ represents the wild-type repressor gene, P⁺ is the promoter, O⁺ is the operator, Z⁺ is the beta-galactosidase gene, and Y⁺ is the permease gene. These components are all functional in this genotype.</span>
3. <span>Step 3: Consider the effect of lactose on the lac operon. Lactose acts as an inducer by binding to the repressor protein (produced by I⁺), causing it to change shape and release from the operator (O⁺), allowing transcription to proceed.</span>
4. <span>Step 4: Consider the effect of glucose on the lac operon. Glucose presence leads to low levels of cyclic AMP (cAMP), which is necessary for the activation of the catabolite activator protein (CAP). CAP-cAMP complex is required for high levels of transcription of the lac operon.</span>
5. <span>Step 5: Determine the level of transcription. In the presence of both lactose and glucose, the repressor is inactive due to lactose, but the low cAMP levels due to glucose mean that CAP is not activated. Therefore, transcription occurs at a basal level.</span>

Key Concepts

Lac Operon Structure

The lac operon in E. coli consists of several key components: the promoter (P), operator (O), and structural genes (Z and Y) that code for enzymes involved in lactose metabolism. The genotype I⁺ P⁺ O⁺ Z⁺ Y⁺ indicates that all necessary elements for operon function are present and functional. Understanding this structure is crucial for analyzing how the operon responds to different growth conditions.

Regulation of the Lac Operon

The lac operon is regulated by the presence of lactose and glucose. When lactose is present, it binds to the repressor protein, allowing transcription to occur. However, the presence of glucose inhibits the operon through catabolite repression, which prevents the activation of transcription even if lactose is available. This dual regulation is essential for understanding transcription levels in various growth media.

Transcription Levels

Transcription levels of the lac operon can be categorized as 'none,' 'basal,' or 'activated.' 'None' indicates no transcription occurs, 'basal' refers to low-level transcription under certain conditions, and 'activated' signifies high transcription rates. In the context of the provided growth medium containing both lactose and glucose, the presence of glucose will lead to 'none' or 'basal' transcription due to catabolite repression, despite lactose being available.