What is the difference between carrier and channel proteins?

Answer 1

Both are integral membrane proteins involved in moving a molecule or ion across a membrane. Both have only one or a couple specific targets, so there are many kinds for specific molecules. The difference is how they accomplish this task.

Carrier proteins transport molecules by changing shape. First, a molecule on one side fits the binding site, and by changing their configuration, the carrier can push the molecule to the other side of the membrane. A macroscopic analog might be a mailbox - a structural change of the transporter (the swinging door) facilitates the movement of a specific shape to the other side. Carrier proteins are affected by temperature and can be saturated (that is, they "max-out" at a rate of transport because there is a finite number of transporter molecules in the membrane and a configuration change is needed for every transport event). To keep the same analogy, the mail door can only swing so fast!

Channel proteins usually transport ions or very small molecules down a concentration gradient, and are more like a hollow tube that can open or shut. They filter and transport molecules based on size and charge. A way to think about this is like a light switch - a on/off switch that allows flow of something (in this case, electricity) to the other side downstream in energy, perhaps doing work in the process. In almost all cases, channels cannot be saturated. If the tube is open, that specific type of molecule can go through without the channel having to change shape.