The cell with the receptor is the one that responds
- The idea
- Predict
- See it
- Why
- Check
The idea
“The cell that makes a signal is the one that responds to it.”
Making a signal sounds like doing something with it, so it's easy to picture the sender reacting. The cell with the receptor is the one that changes.
The short version
The mistake: The cell that makes a signal is the one that responds to it.
What's actually true: The sending cell makes the ligand. The receiving cell makes the receptor, and only a cell with the receptor responds.
- The sending cell expresses the gene for the signal, called the ligand. The receiving cell expresses the gene for the receptor.
- A cell responds only if it has a receptor the ligand fits. A cell can signal itself, but only if it makes the receptor too.
- So in a mutant, ask which cell lost which gene. A cell with no ligand gene can still receive. A cell with no receptor can still send.
On the exam: Find the receptor to find the responder. The sender only needs the gene for the signal.