2. Cell Chemistry & Cell Components
Simple and Facilitated Diffusion
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So now that we know from our last lesson video that facilitated diffusion requires transport proteins, in this video, we're going to talk about some of the transport proteins of facilitated diffusion. And really there are two main types of transport proteins involved in facilitated diffusion. And we have those 2 numbered down below, number 1 and number 2. And so the first type of transport protein involved in facilitated diffusion are the porins, otherwise known as channels. And so as their name implies, porins and channels, they're going to form an obvious membrane spanning tunnel that will allow molecules to move across the membrane, by traveling through the tunnel that these porens or channels create. And so porens implies the word pore and pore is like a hole or like a tunnel. And channels, once again, are basically like tunnels as well. Now aquaporins are specifically used to transport water molecules across or through the cell membrane, essentially facilitating osmosis so that osmosis, the diffusion of water across a semipermeable membrane, can occur at a faster rate, thanks to the aquaporins. Now the second type of transport protein involved in facilitated diffusion are the transporters, otherwise known as carriers. Now the transporters or carriers, unlike the horns and channels, they do not form an obvious membrane spanning tunnel. Instead, the transporters or carriers, they're only open on one side of the membrane at a time, and they must undergo conformational changes in order to move molecules across the membrane. So let's take a look at our image down below to get a better understanding of these ideas. So notice on the left hand side over here what we're showing you are porens and channels. And so notice that porins and channels, they're going to create a membrane spanning tunnel that is basically going to allow molecules to move through the membrane, through the tunnel, and cross to the other side. Now aquaporins are specifically porens that allow water molecules to diffuse across the membrane at faster rates, essentially allowing osmosis to occur faster. And you can see that channels, like ion channels like this, can allow ions that, have charges, like a a positive charge, for example, to move through the tunnel here and get to the other side of the membrane. And so over here, what we see is that there are obvious membrane spanning tunnels, and so there's an opening on both sides of the membrane. Now, when we take a look at the right hand side of the image over here, notice that we're showing you transporters or carrier proteins. And so, when you look at these, notice that it does not form an obvious membrane spanning tunnel like these do over here. Instead, the transporters are only open to one side of the membrane at a time. And so in order to transport these molecules from one side of the membrane to the other side of the membrane, this transporter or carrier protein must undergo a conformational change. And so notice that over here, the transporter or carrier has undergone a conformational change that can allow the molecule on the inside to, be released, to the other side of the membrane. And so, what you'll notice is that, here, the transporter or carrier protein is only open to one side of the membrane, which is over here, and it's closed on this side of the membrane. And so, transporters or carriers are only gonna be open to one side of the membrane at a time, and it's only after the conformational change occurs where they can change their shape and, be open on the other side of the membrane. And so both of these are types of transport proteins involved in facilitated diffusion allowing molecules to be transported down their concentration gradients passively without any energy input. And so this here concludes our lesson on this, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.
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