Read Which Strand Is Transcribed
Promoter orientation determines which strand is read, while eukaryotic RNA polymerases specialise by transcript type.
Transcription is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Orient the transcription unit
RNA polymerase binds the promoter and moves toward the terminator, reading the template strand 3′→5′ while synthesising RNA 5′→3′. Reversing promoter and terminator reverses the transcription direction and swaps coding/template strand roles.
Know the nucleolar polymerase
RNA polymerase I is associated with the nucleolus and synthesises the major rRNA precursor.
Read a transcription Christmas tree
In an electron micrograph of many polymerases transcribing one rRNA gene, the lateral branches are growing rRNA transcripts. They are shortest near initiation and lengthen in the direction of RNA elongation; the central axis is the DNA template. Use branch length to orient the transcription unit. Choose C.
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- ✓Template read 3′→5′; RNA made 5′→3′.
- ✓Promoter direction chooses the template strand.
- ✓RNA polymerase I: major rRNA precursor.
- ✓Growing rRNA transcripts lengthen from the start toward the end of a transcription unit.
The coding strand is not the strand copied directly into RNA.
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