Explain how alternative splicing of a pre-mRNA transcript enables a single gene to produce more than one functional protein.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Pre‑mRNA contains both exons (coding sequences) and introns (non‑coding sequences) that must be processed before translation.
During RNA processing, different combinations of exons can be retained (and/or different exons excluded) to produce distinct mature mRNA molecules from the same pre‑mRNA.
Each distinct mature mRNA is translated to produce a polypeptide with a different amino‑acid sequence (primary structure).
Because protein function depends on its three‑dimensional structure (which arises from its amino‑acid sequence), each polypeptide isoform can have a distinct function.
During RNA processing, different combinations of exons can be retained (and/or different exons excluded) to produce distinct mature mRNA molecules from the same pre‑mRNA.
Each distinct mature mRNA is translated to produce a polypeptide with a different amino‑acid sequence (primary structure).
Because protein function depends on its three‑dimensional structure (which arises from its amino‑acid sequence), each polypeptide isoform can have a distinct function.
Examiner tips
- Use the word ‘exons’ and ‘introns’ – examiners look for correct terminology.
- Show the step‑by‑step flow: pre‑mRNA → alternative splicing → different mature mRNAs → different proteins.
- Mention that the different proteins have different primary structures, leading to different functions.
Common mistakes
- Confusing exons with introns or omitting introns entirely.
- Failing to state that the different mRNAs are translated into different polypeptides.
- Using vague terms like ‘different proteins’ without linking to amino‑acid sequence or function.
Mark scheme (4 marks)
- Pre-mRNA contains both exons (coding sequences) and introns (non-coding sequences) that must be processed before translation.
- During RNA processing, different combinations of exons can be retained (and/or different exons excluded) to produce distinct mature mRNA molecules from the same pre-mRNA.
- Each distinct mature mRNA is translated to produce a polypeptide with a different amino acid sequence / primary structure.
- Because protein function depends on its three-dimensional structure (which arises from its amino acid sequence), each polypeptide isoform can have a distinct function.
Key terms in this question
alternative splicing · pre-mRNA
Related
- All IB DP Biology Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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