Question

How does the binding of the trp corepressor to the trp repressor alter repressor function and transcription? What about the binding of the lac inducer to the lac repressor?

Short answer

The trp repressor gets activated by the trp corepressor that binds to the trp operator. It stops the transcription of the trp operon.

The binding of the lac inducer and lac repressor inactivates the repressor from binding to the lac operator. It does not stop the transcription of the lac operon.

Step-by-step solution

Description of the lac operon

Beta-galactosidase is the enzyme present in the bacteria such as E.coli that digests the lactose sugar. The beta-galactosidase gene is the gene that encodes for the enzyme beta-galactosidase that is a part of the lac operon.

The parts of the lac operon are lac I, lac Z, lac promoter, and lac repressor. The structural component works by switching the gene on and off.

Step 2: Description of the trp operon

E. coli genome contains another type of operon called trp operon, which involves in the tryptophan metabolism. The operon operates in the lower level of tryptophan, and a high level of tryptophan can stop the working of the operon.

The structural components present in the trp operon are trpE, trpD, trpC, trpB, and trpA that regulate the working of the trp operon.

Binding of trp corepressor with the trp repressor

The molecule that indirectly regulates the gene expression by binding with the repressor molecule is a corepressor. The trp corepressor binds with the trp repressor.

This complex goes and binds with the operator molecule and stops the working of the trp operon. The repressor function does change with the binding of the corepressor. Finally, the transcription of the trp operon will get turned off.

Binding of lac inducer with the lac repressor

There is a difference between binding the corepressor with the repressor and the inducer with the repressor. Allolactose is the inducer molecule that binds with the repressor and controls the activity of the repressor.

The lac inducer tends to block the repressor, which does not interrupt the transcription of the lac operon.

Hence, the trp corepressor induces the work of the repressor, and the lac inducer suppresses the work of the lac repressor.