Question

In regulation of gene expression in prokaryotes, choose which among the following options is correct.
I)Lactose acts as the suppressor for the gene expression
II)Tryptophan acts as the inducer for gene expression
III)Regulator gene is the one that produces the repressor molecule.
A. Option I is correct
B. Option II is correct
C. Option III is correct
D. Option II and I are correct
E. Option II and III are correct

Answer 1

Hint: The regulation of the gene expression in prokaryotes occurs at the transcription level where there are two proteins the activators and the repressor where the activators bind to the promoter for the enhancement of the RNA polymerase and the repressor binds to the operator gene to block the action of the RNA polymerase.

Step by step answer:Inducer is a molecule that binds to the repressor and that causes conformational changes in the repressor which can no longer bind to the operator. Allolactose which is an isomer of lactose and binds to the repressor and causes the allosteric shift in the presence of lactose. The altered repressor does not bind to the operator as it allows the RNA polymerase to transcribe the lac genes. So, the lactose serves as an inducer and not as a suppressor. Two tryptophan molecules bind to the trp repressor, where binding activates inactive repressor to bind the trp operator. The binding of tryptophan and repressor complex at the operator prevents the RNA polymerase from binding with the downstream gene that prevents the process transcription. Therefore, tryptophan serves as a compressor and inhibits the expression of genes by indirectly regulating gene expression to the binding repressor and not by directly binding to the DNA. The regulator genes regulate the expression of genes by the protein products which are formed mostly transcription factors, which are also called repressor which binds to the site of RNA polymerase and thus, preventing the binding and transcription.
Hence, the correct option ‘C’.

Note: The regulator genes regulate the expression of genes by the protein products which are formed mostly transcription factors, which are also called the repressor which binds to the site of the RNA polymerase and thus preventing the binding and transcription.