Question

In a transcription unit, the promoter is said to be located towards
A.3' end of the structural gene
B.5' end of the structural gene
C.5' end of the template strand
D.3' end of the non-template strand

Answer 1

Hint: Transcription is the process where an RNA molecule is produced from a template DNA strand. A transcription unit is a portion of the DNA strand which possesses the gene of interest. In any transcription unit, there are many factors responsible for transcription, one such factor would be the promoter region which is present at the 5’ end of the structural gene.

Complete answer:
Transcription is the process wherein the DNA is read and a functional RNA is produced employing a polymerase enzyme. The main function of transcription is to prepare a translatable code of the DNA.
Transcription is controlled by several factors and one important factor is the promoter sequence or promoter unit. As the name suggests this specific sequence promotes the transcription process by enabling the binding of the polymerase enzyme.
The promoter sequence is a 100 to 1000 base pair long DNA sequence present at the beginning of the transcriptional unit or upstream of the structural gene. The coding strand or the sense strand contains legible codable information of the gene which runs from 5’ to 3’ direction and the non-coding or template strand is the strand, which posses the antisense code, which is used as the template, to obtain an mRNA strand with the code present in the sense strand.
Since the structural gene is said to be on the sense strand, the promoter sequence is present on the 5’ end of the structural gene within the transcription unit.
Therefore the correct option is B. 5' end of the structural gene

Note:
The transcription unit has the promoter sequence on the upstream region of the gene or at the beginning of the transcription site.
It promotes transcription by binding to polymerase enzymes and initiating replication.
The promoter sequence is present in both the DNA strands and together aid in the binding of the polymerase enzyme.
But when the question states the position of the structural gene, the promoter site should be mentioned according to the direction of the sense or coding strand. Therefore it’s the 5’ end of the structural gene.