The big idea: Translation can be controlled by how long mRNA lasts. Nucleases break mRNA down; once it is gone, no more of its protein can be made.
The points to remember
- One mRNA molecule can be translated many times while it lasts.
- Nucleases are enzymes that break mRNA down into nucleotides.
- In human cells an mRNA can last from minutes to days.
- Short-lived mRNA gives a short burst of protein; long-lived mRNA gives more protein.
- Controlling degradation is a way to control translation.
Remember it as: No mRNA, no more protein.
Real example: mRNA vaccines. The mRNA in an mRNA vaccine is translated by the body's cells into a virus protein for a short time, then broken down within days, so the protein is made only briefly.
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Short-lived and long-lived mRNA: Cells can make some mRNAs break down quickly and protect others.
| Short-lived mRNA | Long-lived mRNA | |
|---|---|---|
| Lasts | Minutes | Hours to days |
| Protein made | A little, briefly | A lot, for a long time |
| Useful for | Proteins needed only for a moment | Proteins needed in large amounts |
| Control | Production stops soon after transcription stops | Production goes on after transcription stops |
Two levels of control: Transcription controls how much mRNA is made; degradation controls how long it stays. Together they set how much protein a cell makes.
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How it is asked: 1A items: what happens when nucleases bind mRNA (it cannot be translated again), or how a cell stops making too much of a protein (nucleases break down its mRNA).
IB-style questionExplain[2 marks]
Explain how breaking down mRNA can regulate the amount of a protein made by a cell.
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See the answer broken into clear points, with guidance on how each point earns marks.