The end product of a metabolic pathway may bind a repressor to make the latter active enough to bind to operator. In this case the end-product is called as
A
Inducer
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B
Apo-repressor
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C
Co-repressor
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D
Regulator
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Solution
The correct option is C Co-repressor
A substance that inhibits the expression of genes not by direct binding to DNA but instead indirectly regulates gene expression by binding to repressors is known as co-repressor.
For example, in trp operon, two tryptophan molecules serve as co-repressor and bind to the trp repressor. This binding activates the inactive repressor to bind to the trp operator.
Binding of the tryptophan repressor complex at the operator prevents the RNA polymerase from binding the downstream genes and thus presents their transcription.
An inactive repressor that needs the binding of a corepressor for activation is termed as an apo-repressor or inactive repressor.
When tryptophan is not present in the cell, the repressor is inactive and can not bind to the operator and is called apo-repressor.
A molecule, that regulates gene expression by binding to repressors or activators to prevent or start the transcription, respectively, is inducer.
Allolactose serves as an inducer in the lac operon and binds to the repressor and decreases the repressor's affinity for the operator site; thereby facilitating transcription.
A regulator gene controls the expression of one/more genes by its encoded repressor proteins.