Transporter and Transport Proteins Types – Biological Membranes

by Kevin Ahern, PhD

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    00:00 Now I've been describing various transport systems to you, and I want to give you some nomenclature that is important to understand. So the first nomenclature here is what we describe as a uniport. A uniport involves the movement of one molecule in one direction.

    00:17 So the GLUTs that I talked about for example, are moving glucose into the cell, and that's one molecule moving in one direction. A synport is a transport system that moves two molecules in one direction. Now I haven’t described any here, but there are systems that will bring multiple molecules in, of different types, as the A and B shown here. I should also note that some people use the term symport, s-y-m instead of 's-y-n, but they both refer to the same thing. Last there's an antiport. Now an antiport as its name would suggest, is a system that moves two molecules and they move them at opposite directions. That was what happened as we saw in the sodium-potassium ATPase and it is also what happened with the sodium-calcium transport system. Now in addition to these names right here, there are two others that I want to bring up. One is if the movement of molecules results in a net change in charge, such as we saw with the sodium-potassium ATPase, we describe that system as electrogenic, creating an electrical gradient. If the movement results in no change in charge, such as would happen if we move glucose across the membrane, the net movement is described as electroneutral.

    01:31 Now, earlier I talked about proteins that were involved in controlling the movement of ions across cell membranes. Now I want to say a little bit more about some of those proteins. So first of all carrier proteins are proteins like the sodium-potassium ATPase that I described that grab and move specific molecules across the membrane. They are typically either active transport or facilitated diffusion, but they're not openings in the cell membrane.

    01:57 A remarkable set of proteins that specifically allows the movement of specific ions are called ion channel proteins, and I refer to them earlier but I want to say a little bit about them right now. Ion channel proteins rely on diffusion, meaning that they don't have for example, an active transport, but the cell has ion channel proteins because, first of all, as I said, they allow specific ions to move across the membrane. This happen for example, when I described the movement of sodium into a nerve cell. The movement of sodium into a nerve cell happened because an ion channel protein open and allow the sodium to come in. Now a simple system like this is incredibly powerful because the opening, like I described, can allow diffusion to happen, and diffusion happens extremely rapidly. So because of this, the ion channel proteins can allow a big change in ion concentration as a result of a very simple thing happening. Now, ion channel proteins really need to be controlled, because if they're not controlled that ionic environment can change too drastically, and we've seen or heard the consequences of that with respect to osmotic pressure, and so forth. So controlling ion channel proteins is something I want to discuss.

    About the Lecture

    The lecture Transporter and Transport Proteins Types – Biological Membranes by Kevin Ahern, PhD is from the course Biochemistry: Basics.

    Included Quiz Questions

    1. They create electrical gradients across the cell membrane.
    2. They do not change the charge across a membrane as a result of their actions.
    3. They are always uniports.
    4. They always involve sodium.
    5. The movement of glucose across the cell membrane is an example of an electrogenic transport system.
    1. Sodium-potassium ATPase is an example of synport.
    2. Antiporters move two or more different molecules in opposite directions across the cell membrane.
    3. The net movement of glucose across the membrane is described as electroneutral.
    4. Symporters move molecules in the same direction across the cell membrane.
    5. Ion channels allow the movement of specific ions, and they rely on diffusion.

    Author of lecture Transporter and Transport Proteins Types – Biological Membranes

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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