Transcription and RNA Processing
▶︎ Watch it animatedinteractive step-through · ~3 min · optionalTranscription is the first step of gene expression, and Topic 6.3 is where you learn exactly what it makes — and what it does not. Transcription copies a gene's DNA into RNA; it does not build a protein. The enzyme that does the work is RNA polymerase, which reads one strand of the DNA — the template strand — in the 3′→5′ direction and assembles a complementary messenger RNA in the 5′→3′ direction, adding each new nucleotide to the growing strand's 3′ end. Keep those two arrows straight and the rest of the unit follows.
Transcription and RNA Processing · Open the full sandbox →In eukaryotes the RNA that comes straight off the gene is not ready to use. This first transcript, the pre-mRNA, is edited inside the nucleus before it can leave. Three processing steps turn it into a mature mRNA: a modified 5′ cap is added to the front, a poly-A tail of many adenines is added to the back, and the introns — the non-coding stretches — are spliced out so the remaining exons join into one continuous coding message. The cap and tail protect the transcript and help it get exported and translated; splicing removes the parts that don't code.
- Transcription makes RNA, not protein. Its product is an mRNA transcript; building a protein from that transcript is translation, a separate step.
- RNA polymerase is the enzyme of transcription. It transcribes the gene — no primer or DNA polymerase involved in making the message.
- The template strand is read 3′→5′; the new mRNA is built 5′→3′. Nucleotides are added to the transcript's 3′ end, so the two strands run antiparallel.
- Pre-mRNA is processed before it leaves the nucleus. A 5′ cap and a poly-A tail are added, and introns are spliced out so the exons join into the mature mRNA.
The mistakes here cluster around a few failure modes. One is thinking transcription makes protein — collapsing transcription and translation into a single step, or naming the wrong enzyme, when transcription's only product is an RNA copy made by RNA polymerase. Another is getting the directions backward — reading the template 5′→3′ or building the transcript the wrong way. And the third is misreading RNA processing — thinking the cap, tail, or splicing happens on protein, or that introns are kept and exons discarded, when in fact the introns are removed and the exons are joined. Every scenario in this topic asks you to keep those distinctions clean.
The work
3 ways in · any order
Lesson
Transcription and RNA Processing
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Transcription copies a gene into RNA — not protein — with RNA polymerase reading the template strand 3′→5′ and building the mRNA 5′→3′. In eukaryotes the pre-mRNA is then processed: a 5′ cap and a poly-A tail are added, and introns are spliced out so the exons join. The lesson walks the ways students misread that — fusing transcription with translation, flipping the directions, or garbling what processing keeps and removes — across ten scenarios.
Diagnostic
10-item topic check
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Ten items on transcription and RNA processing — that transcription makes an RNA copy, not a protein, using RNA polymerase (U6-BIO6); that the template strand is read 3′→5′ while the mRNA is built 5′→3′, so the directions can't be flipped (U6-BIO1); and that pre-mRNA is processed with a 5′ cap, a poly-A tail, and introns spliced out so the exons join (U6-BIO7). Take it cold to surface which of these are still tangled, or after the lesson to confirm they hold.
Targeted Practice
Drill a single misconception
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Pick one of the failure modes you missed and drill it on its own. The round is adaptive: two correct in a row clears it for now and moves you to the next. Two in a row is a checkpoint, not proof: if the error resurfaces later, the misconception comes back.