AP BIOLOGY

Detailed explanation-1: -The operator is a DNA sequence present between the promoter region and the first coding gene. This operator region serves as repressor protein binding site; option B is correct.

Detailed explanation-2: -These proteins bind to regions of DNA, called regulatory elements which are located near promoters. The promoter is the region of a gene where RNA polymerase binds to initiate transcription of the DNA to mRNA. After regulatory proteins bind to regulatory elements, the proteins can interact with RNA polymerase.

Detailed explanation-3: -The operator is a special DNA sequence located between the promoter sequence and the structural genes that enables repression of the entire lac operon, following binding by the inhibitor (lac i) protein. Expression of the lac operon is, in fact, regulated by the presence of lactose itself.

Detailed explanation-4: -Some regulatory proteins are repressors that bind to pieces of DNA called operators. When bound to its operator, a repressor reduces transcription (e.g., by blocking RNA polymerase from moving forward on the DNA).

Detailed explanation-5: -Most of the operons involved in amino acid synthesis are regulated by these two mechanisms. The trp operon is negatively controlled by the trp repressor, a product of the trpR gene. The trp repressor binds to the operator and blocks transcription of the operon.