Question

The transcription unit is represented by the following diagram. Select the correct answer based on this.

(a)A- Promoter B-terminator C-coding strand D- structural gene
(b) A- Promoter B- coding strand C- terminator D- structural gene
(c) A- Terminator B- coding strand C- structural gene D- promoter
(d) A- Promoter B- structural gene C-coding strand D- terminator

Answer 1

Hint: The process of mRNA synthesis using DNA coding strand as the template is known as Transcription and it occurs in the nucleus.

Complete answer:
The transcription unit has three regions in DNA and they are a promoter, the structural gene, and terminator. RNA polymerase binds to the promoter which is found near the beginning of the gene i.e. near the 3’- end. The DNA opens up in the promoter region and each gene has its promoter. So A is a promoter and B is a structural gene.
One strand of DNA (template strand) acts as a template and as RNA polymerase reads this template it builds an RNA molecule out of complementary nucleotides, making a chain that grows from 5' to 3'. RNA polymerase moves forward along the template strand which is in the 3' to 5' direction. The RNA transcript (coding strand) carries similar information as the DNA but is present with uracil (U) instead of thymine (T). So C is a coding strand.
Terminators signal that the RNA transcription is complete. They tell the transcript to be released from the RNA polymerase. Here it is present near the 5’-end of the template strand. So D is a terminator.
So, the correct answer is ‘A- Promoter B- structural gene C-coding strand D- terminator’.

Note: A sequence of nucleotides in DNA or RNA that encodes the synthesis of a gene product (either RNA or protein) is known as a gene. A gene is a physical and functional unit of heredity and is made up of DNA.