Edexcel A Level (IAL) Biology -3.19 Post-Transcriptional Changes to mRNA- Study Notes- New Syllabus
Edexcel A Level (IAL) Biology -3.19 Post-Transcriptional Changes to mRNA- Study Notes- New syllabus
Edexcel A Level (IAL) Biology -3.19 Post-Transcriptional Changes to mRNA- Study Notes -Edexcel A level Biology – per latest Syllabus.
Key Concepts:
- 3.19 understand how one gene can give rise to more than one protein through post-transcriptional changes to messenger RNA (mRNA)
How One Gene Can Give Rise to More Than One Protein
📌 Introduction
Although each gene codes for a specific protein, one gene can actually produce several different proteins. This happens because of post-transcriptional modifications — changes made to the mRNA molecule after transcription but before translation.
🧩 Key Concept
Post-transcriptional modification = processing of pre-mRNA (the first copy made from DNA) into mature mRNA.
During this process, different combinations of exons (coding regions) may be joined together, while introns (non-coding regions) are removed.
This allows one gene → many possible mRNA forms → many possible proteins.
🔄 The Process Explained
- Step 1: Transcription
DNA → pre-mRNA (contains both exons + introns). - Step 2: Splicing
Introns are removed.
Exons are spliced (joined) together to form mature mRNA. - Step 3: Alternative Splicing
Different exons can be joined in different combinations.
Each unique combination forms a slightly different mRNA → different protein.
🧠 Example
Imagine exons as letters: A–B–C–D
Normal splicing: A + B + C → Protein 1
Alternative splicing: A + C + D → Protein 2
So, one gene can make Protein 1 and Protein 2 depending on which exons are included.
🧬 Other Post-Transcriptional Modifications
| Type | Description | Effect |
|---|---|---|
| Capping (5′ cap) | Addition of methylated cap at mRNA start | Protects mRNA from damage, helps ribosome binding |
| Poly-A tail (3′ end) | Addition of adenine bases | Increases mRNA stability |
| RNA editing | Some bases changed chemically | Alters amino acid sequence → different protein form |
🧫 Biological Importance
| Function | Explanation |
|---|---|
| Protein diversity | Increases number of proteins without increasing number of genes |
| Tissue specificity | Same gene can make different proteins in different tissues |
| Regulation | Allows cells to adapt protein production to needs (e.g., stress, growth) |
⚡ Quick Recap
Gene → pre-mRNA → mature mRNA → protein
Alternative splicing → exons rearranged → different proteins
One gene = many proteins
Gives flexibility & diversity without extra genes
Common in humans — explains how ~20,000 genes produce >100,000 proteins