Question

Explain the transcription unit.

Hint:

Promoter (start) → structural gene (copied) → terminator (stop).

Answer 1

Step 1: Definition:
A transcription unit is a segment of DNA that has the three components needed to be transcribed into RNA by RNA polymerase: a promoter, a structural gene, and a terminator.

Step 2: The three components:
(1) Promoter — located upstream (towards the 5' end of the coding/sense strand), it is where RNA polymerase binds and it decides which of the two DNA strands is transcribed (the template strand) and the direction of transcription. (2) Structural gene — the region actually transcribed into RNA, read from the template strand in the 3'→5' direction to make an RNA that is complementary and antiparallel to it. (3) Terminator — located at the downstream (3') end of the coding strand, it marks the point where transcription stops.

Final Answer:
A transcription unit = promoter + structural gene + terminator, together defining where transcription starts, what is copied, and where it ends.