Explain how the process of splicing of pre-mRNA contributes to proteome diversity in eukaryotes.

IB DP Biology Higher Level (2023 syllabus) — D1.2 Protein synthesis · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Pre‑mRNA contains both introns (non‑coding) and exons (coding) that must be processed before translation.
Introns are removed and exons are joined together during splicing to form mature mRNA.
Alternative splicing allows different combinations of exons to be included in the mature mRNA from the same pre‑mRNA / gene.
This produces multiple different polypeptides / proteins from a single gene, increasing the size of the proteome beyond what the number of genes alone would allow.

Examiner tips

Use the exact terms ‘pre‑mRNA’, ‘introns’, ‘exons’, ‘splicing’, ‘alternative splicing’, ‘proteome diversity’.
Show the logical sequence: pre‑mRNA → splicing → mature mRNA → alternative combinations → multiple proteins.
Keep the answer concise – 4 points, one sentence each.

Common mistakes

Confusing introns with exons or vice versa.
Failing to mention alternative splicing as the mechanism that creates diversity.
Using vague language such as ‘different proteins’ without linking to exons and splicing.

Mark scheme (4 marks)

Pre-mRNA contains both introns (non-coding sequences) and exons (coding sequences) that must be processed before translation.
Introns are removed and exons are joined together during splicing to form mature mRNA.
Alternative splicing allows different combinations of exons to be included in the mature mRNA from the same pre-mRNA / gene.
This produces multiple different polypeptides / proteins from a single gene, increasing the size of the proteome beyond what the number of genes alone would allow.

Key terms in this question

pre-mRNA · splicing · proteome