A Levels Biology (9700)•9700/11/M/J/22

Explanation
Non-template strand in transcription
Steps:
- Recall that transcription uses the template strand to synthesize RNA, while the non-transcribed (coding) strand has the same sequence as the mRNA (with T instead of U).
- In diagrams, the template strand is shown being read 3' to 5' by RNA polymerase, with RNA growing 5' to 3'.
- Identify the strand not bound to or read by the polymerase as the non-transcribed one.
- Match diagram labels: the strand parallel but not antiparallel to emerging RNA indicates the coding strand.
Why A is correct:
- Option A depicts the strand matching mRNA sequence, defining it as the non-template (coding) strand per central dogma.
Why the others are wrong:
- B shows the template strand, as it's antiparallel and read by polymerase.
- C illustrates the RNA transcript, not a DNA strand.
- D labels the promoter region, unrelated to transcribed/non-transcribed strands.
Final answer: A
Topic: Protein synthesis
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