Give falsifications for the incorrect choices and a an explanation of the correc

Question

Give falsifications for the incorrect choices and a an explanation of the correct answer thanks

Michael Munr Lecture 34: Which is True? A bacterial operon encodes the enrymes roquired for the bionynethesis of en essential macromolecule ". The opcron is regalated by a repressor protcia and "Qf" is as allosteric effector of this repressor. Which of the following is trve A When " binds to the repressor, the repressor binds to the eperator ?.when "Q. beds to the operator, RNA polymerase can bend to the pennter C. When "Q binds to the promoter, the repressor cannot bind so the operator D. When "Q hinds to the repressor, the repressor can hind to RNA polymera Reply

Explanation / Answer

An operon is a cluster of genes under a common promoter which facilitates productions or a certain protein. Here the operon produces the macromolecule Q. When the macromolecule is not required, a repressor protein switches off the operon and Q is not produced. The repressor is activated when Q binds to its allosteric site (an auxillary site away from the active site that changes the shape of the active site). So there is feedback inhibition that comes into play when excess Q is produced, so it binds to the repressor and inhibits the production of more of Q by switching off the operon.

A.This is the correct response as explained above. Q binds to the repressor at the allosteric site(it is an effector of this repressor), which changes the shape of the active site of the repressor and the repressor is able to bind to the operator.

B. The only way Q can be an allosteric effector of the repressor is when it binds to the repressor. So Q does not bind to the operator.

C. There is no competition between the molecule Q and the repressor protein to bind to the promoter. The only way Q can be an allosteric effector of the repressor is when it binds to the repressor.

D. This is one method by which synthesis of molecule Q can also be stopped but repressor proteins bind to the operon to inhibit it. The RNA polymerase is already bound to the promoter and when the repressor binds to the operator sites as well, it prevents the RNA polymerase to leave the promoter due to which transcription does not proceed to the elongation step and the operon is inhibited.

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