Binding alone doesn't name a membrane protein's job
- The idea
- Predict
- See it
- Why
- Check
The idea
“A protein that grabs a molecule is an enzyme, and one that holds on is an anchor.”
Almost every membrane protein holds onto something, so grabbing looks like catalysis and holding looks like anchoring.
The short version
The mistake: A protein that grabs a molecule is an enzyme, and one that holds on is an anchor.
What's actually true: It may relay a signal, speed a reaction, move a substance or hold on. What it binds and what follows tell you which.
- A receptor binds a signal, like a hormone, and relays it inside without changing it. An enzyme speeds up a reaction that changes its substrate.
- Junction proteins grip neighboring cells. Anchoring proteins grip the cell's own cytoskeleton and help hold its shape.
- A transporter moves a substance across the membrane. Some proteins do several jobs, so go by the evidence in the question.
On the exam: Ask what the protein binds and what happens next.