A laboratory scientist notices that a certain bacterium does not utilize lactose when glucose is available in its environment. Describe a cellular regulatory mechanism that would explain this observation.

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Identify the phenomenon described: the bacterium does not utilize lactose when glucose is present, which suggests a regulatory mechanism controlling the use of alternative sugars based on glucose availability.

Recall the concept of catabolite repression, a common bacterial regulatory mechanism where the presence of a preferred carbon source (like glucose) inhibits the metabolism of other sugars (like lactose).

Explain that in the presence of glucose, the levels of cyclic AMP (cAMP) inside the bacterial cell are low, which affects the activity of the catabolite activator protein (CAP).

Describe how low cAMP means CAP cannot bind effectively to the promoter region of the lac operon, reducing transcription of genes needed for lactose metabolism.

Conclude that this regulatory mechanism ensures the bacterium prioritizes glucose metabolism over lactose, conserving energy by not producing unnecessary enzymes when glucose is available.

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Catabolite Repression

Catabolite repression is a regulatory mechanism where the presence of a preferred carbon source, like glucose, inhibits the use of alternative sugars such as lactose. This ensures the bacterium conserves energy by metabolizing the most efficient nutrient first.

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03:42

Repressible Operons

Lac Operon Regulation

The lac operon controls the metabolism of lactose in bacteria. It is activated only when lactose is present and glucose is absent, allowing the production of enzymes needed to break down lactose. Glucose presence suppresses this operon’s activation.

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07:06

The Lac Operon

cAMP-CAP Complex

When glucose levels are low, cyclic AMP (cAMP) levels rise and bind to the catabolite activator protein (CAP). This complex enhances transcription of the lac operon. High glucose reduces cAMP, preventing CAP binding and thus repressing lactose metabolism.

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