A slowdown isn't always a gene switched off
- The idea
- Predict
- See it
- Why
- Check
The idea
“If an enzyme's output drops, the cell must have turned its gene off.”
Class time goes mostly to gene regulation and operons. So when a cell makes less of something, you think of the gene first.
The short version
The mistake: If an enzyme's output drops, the cell must have turned its gene off.
What's actually true: Cells can act at transcription, mRNA breakdown, translation, protein breakdown or enzyme activity. The data show which.
- DNA is transcribed into mRNA, and mRNA is translated into protein. Control at one step changes that step and the ones after it.
- If mRNA fell, the gene is transcribed less or its mRNA breaks down faster. If mRNA held steady but protein fell, translation slowed or the protein breaks down faster.
- If only activity fell, the enzyme itself changed. An inhibitor may bind it, or a phosphate may be added. That can happen in seconds.
- An end product can inhibit its enzyme in seconds and repress its genes more slowly. Name the level your data show.
On the exam: Find the earliest level that changed. That's where the control acts.