Question

Now try adding the laci promoter (another cis-acting element) and the laci gene (the dna that encodes the lac repressor protein, which is a type of trans-acting element) to the stretch of dna. what happens?

Answer 1

Adding the laci promoter and gene introduces a regulatory mechanism to the lac operon, enabling the lactose-dependent expression of genes lacZ, lacY, and lacA through the action of the lac repressor protein.

Step-by-step explanation:

When adding the laci promoter and the laci gene to the stretch of DNA that includes the lac operon, we are introducing elements that will regulate the expression of the lacZ, lacY, and lacA genes. The lacI gene produces the lac repressor protein, which is a trans-acting element that can bind to the operator region of the lac operon. In the absence of lactose, the repressor binds to the operator, preventing the binding of RNA polymerase to the promoter, thus inhibiting the expression of lac operon genes.

When lactose is present, it is converted into allolactose, which binds to the repressor. This binding causes an allosteric change in the repressor, preventing it from binding to the operator and allowing RNA polymerase to transcribe the lac operon genes. As a result, the proteins needed for lactose metabolism are synthesized.