Question

Evaluate these statements about regulation of the lac operon. Select True or False for each statement.
T/FThe lac operon is transcribed at the highest rate when extracellular glucose and lactose are abundant.
T/FThe repressor protein is bound to DNA of the operator when lactose is present.
T/FA mutation in the operator is likely to prevent transcription of the lac operon under any condition.
T/FA mutation that alters the catabolite activator protein is predicted to alter the regulation of many different operons.

Accepted Answer

Understand the lac operon: The lac operon is a set of genes in bacteria that are involved in lactose metabolism. It is regulated by the presence or absence of lactose and glucose, as well as by the activity of regulatory proteins like the repressor and the catabolite activator protein (CAP). Analyze the first statement: 'The lac operon is transcribed at the highest rate when extracellular glucose and lactose are abundant.' Recall that glucose inhibits the activity of CAP, which is necessary for high transcription rates of the lac operon. Therefore, transcription is not at its highest when glucose is abundant, even if lactose is present. Analyze the second statement: 'The repressor protein is bound to DNA of the operator when lactose is present.' Remember that lactose (or its isomer allolactose) binds to the repressor protein, causing it to change shape and release from the operator. This allows transcription to proceed. Thus, the repressor is not bound to the operator when lactose is present. Analyze the third statement: 'A mutation in the operator is likely to prevent transcription of the lac operon under any condition.' Consider that a mutation in the operator could either prevent the repressor from binding (leading to constant transcription) or disrupt the operator's function entirely, which might prevent transcription. The specific effect depends on the nature of the mutation. Analyze the fourth statement: 'A mutation that alters the catabolite activator protein is predicted to alter the regulation of many different operons.' Recall that CAP is a global regulatory protein that affects the transcription of multiple operons, not just the lac operon. A mutation in CAP would likely impact the regulation of many operons that rely on CAP for activation.

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Concetti chiave

Lac Operon Structure and Function

Repressor Protein and Induction

Catabolite Activator Protein (CAP) and Positive Regulation