 think it was really clear that I wanted to keep talking in that last lecture because carriers are really cool and this is all facilitated diffusion so the only difference is whether we're going through a carrier or whether we're going through a channel. Carriers here's the take-home message they are only open to one side at a time. Okay think about that. I think of carriers as little like Pac-Man things that can open in to the cell or they can open out of the cell. They can't be open to in and out both at the same time. Contrast that with the channel. The channel is a tube and when the tube is open if it's a gated channel and that channel is open it's a direct path between the extracellular fluid and the intracellular fluid. Which one's going to be faster do you think? Is it going to be faster for molecules to move through a channel or through a carrier? Channels are faster. In fact there are water channels that allow I don't know it was like within one second like a hundred million miles. I can't remember what the fact was. It's something absurd how quickly water can move in and out of a channel as opposed to a carrier that has to change its confirmation in order to move something through and really carriers move things through like one at a time. Channels move things through one at a time but you can get a really fast line right you can get like everybody can crowd into line together and they might have to go through single file but everybody's trying to get through and they can make it happen. The carrier is like like that roundy round door where you know what if that thing fills up okay that was a bad example but it has you have to get all the way through everybody has to get all the way through before the next group can get back in. Did you fall like what nobody knows what I just said okay so we now have a sense of why carriers are different than channels but they're doing the same thing so we're just moving molecules in this case we're moving the green things you can see here we've got a green thing going in usually in a carrier the molecule that's being moved has a binding site in the carrier and the carrier what is it it's a protein that's what the channel is too channels are proteins and often when something binds to a protein it changes its shape so the molecule binds to the carrier protein that changes its shape and the shape change usually opens the molecule the carrier to a different direction we're now facing inside or outside opposite of what we were and the binding site usually goes away once the binding site goes away the molecule falls off and is now in on the other side of the cell membrane all of our carriers work the same way these guys just do facilitated diffusion because they're moving molecules down their cell member down their concentration gradient through the some okay let's talk about active transport next