Question

Which of the following statements are correct with reference to a transcription unit in DNA? A. A transcription unit in DNA is defined primarily by three regions: promoter, structural gene and terminator.
B. The promoter is said to be located towards the $5'$-end of the structural gene.
C. The promoter is a DNA sequence that provides binding site for RNA polymerase.
D. The promoter defines the template and coding strands.
E. The terminator is located towards the $3'$-end of the coding strand and it defines the end of the process of transcription.

• A. A, C, D and E only
• B. A, B, C, D and E
• C. A, B, C and D only
• D. B, C, D and E only

Hint:

Crucial Rule: All "ends" ($5'$ or $3'$) in transcription unit descriptions are given with respect to the \textbf{Coding Strand}, even though the coding strand doesn't actually code for anything!

Answer 1

The Correct Option is B

Step 1: Understanding the Question
The question asks to verify several statements about the structure and conventions of a transcription unit in DNA. A transcription unit is the sequence of DNA that acts as a template for RNA synthesis. Step 2: Key Formula or Approach
To solve this, understand the parts of a transcription unit and the nomenclature rules: - Promoters are "start" signals. - Terminators are "stop" signals. - By convention, all numbering and positioning (5' or 3') are based on the coding strand (not the template strand). Step 3: Detailed Explanation
Statement A: A transcription unit consists of the promoter, the structural gene (to be copied), and the terminator. This is correct.
Statement B: The promoter is located at the 5'-end (upstream) of the structural gene (referenced to the coding strand). This is correct.
Statement C: The promoter is the DNA sequence where RNA polymerase enzyme binds to initiate the process. This is correct.
Statement D: By binding to the asymmetric promoter, the enzyme knows which direction to travel, which effectively decides which strand will be the template. This is correct.
Statement E: The terminator is at the 3'-end (downstream) of the coding strand and signifies the finish line for transcription. This is correct.
Step 4: Final Answer
Since all five statements are factually accurate according to molecular biology principles, option (D) is the correct answer.