Signals multiply in the relay, not at the receptor
- The idea
- Predict
- See it
- Why
- Check
The idea
“A signal gets amplified at the surface, because each signal molecule switches on many receptors.”
A tiny signal sets off a huge response, so the boost seems to happen at the surface. Binding a receptor only starts the message.
The short version
The mistake: A signal gets amplified at the surface, because each signal molecule switches on many receptors.
What's actually true: Binding a receptor starts the signal. Relay enzymes inside the cell multiply it, because each acts on many molecules.
- Reception, the binding step, starts the signal without multiplying it. The gain comes later, in transduction, the relay inside the cell.
- When a relay protein is an enzyme, one active copy acts on many molecules, so each enzyme step multiplies the signal.
- In the cAMP pathway, the receptor switches on several G proteins, the first gain. Not every step multiplies. G protein to adenylyl cyclase is one to one.
On the exam: Binding starts the signal. Relay enzymes multiply it, because each one acts on many molecules.