AP BIOLOGY

Detailed explanation-1: -In molecular genetics, a repressor is a DNA-or RNA-binding protein that inhibits the expression of one or more genes by binding to the operator or associated silencers. A DNA-binding repressor blocks the attachment of RNA polymerase to the promoter, thus preventing transcription of the genes into messenger RNA.

Detailed explanation-2: -The lac repressor protein binds to the operator and blocks RNA polymerase from binding to the promoter and transcribing the operon. The promoter is the binding site for RNA polymerase, the enzyme that performs transcription. The operator is a negative regulatory site bound by the lac repressor protein.

Detailed explanation-3: -A repressor protein binding to the operator gene prevents the transcription of the structural genes for the operon in the absence of inducer.

Detailed explanation-4: -A repressor protein binds to a site called on the operator. In this case (and many other cases), the operator is a region of DNA that overlaps with or lies just downstream of the RNA polymerase binding site (promoter).

Detailed explanation-5: -Repressor proteins can be DNA– or RNA-binding: DNA-binding repressors – block the binding of RNA polymerase to the promoter. As a result, the gene is prevented from being transcribed into mRNA. RNA-binding repressors – bind to mRNA, preventing protein translation.