Small molecules change genes through a protein
- The idea
- Predict
- See it
- Why
- Check
The idea
“The signal molecule binds the DNA itself and switches the gene on or off.”
It's easy to picture a sugar or hormone landing right on the gene it turns on. There's a protein in between that does the DNA part.
The short version
The mistake: The signal molecule binds the DNA itself and switches the gene on or off.
What's actually true: A small molecule binds a protein, such as a repressor or receptor, and a protein carries the change to the DNA.
- Proteins bind specific DNA sequences. Repressors, activators and other transcription factors each fit a particular sequence near a gene.
- A small molecule binds one of those proteins and changes its shape. In the lac operon, allolactose, the inducer, binds the repressor so it lets go of the operator.
- A signal that stays outside the cell binds a membrane receptor. A relay of proteins inside then changes a transcription factor.
On the exam: When a small molecule changes a gene, find the protein it binds. Proteins are what grip the DNA.