You are studying the lac operon Explain the role of allolact

You are studying the lac operon. Explain the role of allolactose in regulation of the lac genes. Explain why the lac genes are not transcribed in the presence of glucose. You isolate a mutant in which the lac promoter is never induced! Propose a mechanism (in which regulatory element might there be a mutation?).

Solution

a). Allolactose is an inducer of lac operon in E.coli. Binding of allolactose to the lac repressor bring conformational changes, which results in reduced binding affinity of the lac repressor to the operator region. In the absence of repressor, the transcription proceeds further.

b).

The lac operon is under both the positive and negative regulation. This dual regulation allows the cell to choose the regulation under different conditions. For example, if a cell is supplied with both the glucose and lactose, the cell chooses glucose, this is possible because of dual regulation.

In the presence of glucose, the synthesis of beta galactosidase is repressed until all the glucose available is oxidized. This helps to conserve energy and utilizes it to synthesize the Lac enzymes before going through creating the machinery required for lactose metabolism.

Lactose is an inducer molecule of lac operon, when inducer binds to the repressor, its shape is altered, in this state; operator cannot bind to the repressor. Operator is a part of operon, which is a DNA binding site for a repressor, binding of repressor to the operator site terminates the process of transcription in prokaryotes.