Final answer:
The promoter is part of the DNA that initiates transcription and is not included in either the primary transcript or the mature mRNA. Instead, mature mRNA comprises only exons after introns are removed during processing, and it consequently lacks the DNA's promoter region.
Step-by-step explanation:
The primary product of transcription, known as pre-mRNA, includes regions not found in mature mRNA molecules. These regions include exons, introns, a promoter, and other elements involved in the regulation and initiation of transcription. Following transcription, pre-mRNA undergoes processing where introns are removed, and exons are spliced together. The resulting mature mRNA contains the exons which code for the protein, as well as a 5' cap and a poly-A tail, but it does not contain a promoter, which is only needed for the initiation of transcription (transcription initiation).
Among the answer choices for the question "Which of the following is found on the primary product of transcription but not on a mature mRNA molecule?" are:
- Start codon
- Promoter
- Exons
- Introns
- Stop codon
The correct answer is that the promoter is a region of the DNA that facilitates the start of transcription but is not included in the mRNA, whether primary or mature. All other options listed are either retained in the mature mRNA (start codon, exons, and stop codon) or are removed from the pre-mRNA during processing to form mature mRNA (introns).