A Levels Biology (9700)•9700/11/M/J/25

Explanation
RNA Splicing Removes Introns in Eukaryotes
Steps:
- Identify non-coding RNA sequences: These are introns, which do not code for proteins.
- Recall transcription process: In eukaryotes, pre-mRNA contains both exons (coding) and introns (non-coding).
- Understand removal step: After transcription, introns are spliced out to form mature mRNA.
- Match to cell type: This splicing occurs only in eukaryotic cells, not prokaryotes.
Why B is correct:
- Introns are non-coding sequences removed via splicing in eukaryotic cells, as defined in molecular biology for mRNA processing.
Why the others are wrong:
- A: Exons are coding sequences retained, not removed, in eukaryotes.
- C: Exons are coding and not removed; prokaryotes lack introns entirely.
- D: Introns exist but are not removed in prokaryotes, which have simpler transcription without splicing.
Final answer: B
Topic: Protein synthesis
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