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Question

Biology Question on the molecular basis of inheritance

In negative operon

A

co-repressor binds with repressor

B

co-repressor does not bind with repressor

C

co-repressor binds with inducer

D

CAMP have negative effect on lac operon.

Answer

co-repressor binds with repressor

Explanation

Solution

The tryptophan operon (trp operon) in bacteria is a repressible operon. Here repressor is inactive and it becomes active as DNA binding protein only when complexed with a co-repressor (tryptophan). In absence of tryptophan, the operator site is open to binding by RNA polymerase, which transcribes the structural genes of tryptophan operon, leading to production of enzymes that synthesize tryptophan. When tryptophan becomes available, the enzymes of tryptophan synthetic pathway are no longer needed and tryptophan (co-repressor)-repressor complex blocks transcription. The regulation of this operon is also a negative control.