Channels are open pores, carriers change shape
- The idea
- Predict
- See it
- Why
- Check
The idea
“A channel grabs each molecule and flips it across. A carrier is an open tunnel.”
Both proteins sit in the membrane and let solutes move down a gradient. It's easy to memorize that one changes shape and attach that fact to the wrong name.
The short version
The mistake: A channel grabs each molecule and flips it across. A carrier is an open tunnel.
What's actually true: A channel is an open pore that solutes pass straight through. A carrier binds each molecule and changes shape to move it.
- A channel has a water-filled pore. Ions or water pass straight through without the protein changing shape, so channels are fast.
- A gated channel changes shape to open or close, for example when a ligand binds. One opening lets many ions through.
- A carrier binds a molecule on one side, then changes shape to release it on the other. Each trip takes time, so carriers are slower and can saturate.
On the exam: A shape change for each molecule means a carrier. A pore the solute flows through means a channel.