Which describes a promoter?
a. the first part of an operon that regulates where, when, and to what level a gene is expressed
b. the part of an operon that, if attached by a repressor protein, suppresses the expression of a gene
c. a cluster of genes that are expressed or repressed as a group
d. an enzyme that dna unzip prior to transcription.

Answer;

a. A promoter is a sequence of nitrogenous bases in DNA that signals the DNA polymerase to begin to transcribe the gene.

Explanation;

-Promoters are DNA sequences located in the 5' region adjacent to the transcriptional start site. RNA polymerase and transcription factors bind to the promoter to initiate production of an mRNA transcript (transcription).

-It includes the binding site for RNA polymerase, the transcription start site, and sites where proteins that are responsible for regulating gene expression (transcription factors) can bind.