Active Transport: Sodium-calcium Exchanger – Biological Membranes

by Kevin Ahern, PhD

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    00:00 Now, active transport as I said before can have a variety of energy sources. One of the energy sources we saw with the sodium potassium ATPase was ATP energy, but ATP is only one source of energy to move ions across, or move other substances across a membrane. A really good example is shown here. This is the sodium calcium pump, and the sodium-calcium pump uses the sodium gradient to move calcium across a lipid bilayer. This is illustrated in the slide here. Now you can see the protein that's involved in this transport is shown in green.

    00:39 And as you look at this you can see that you have in the case of this, you have the intracellular space on the bottom and the extracellular space or the portion outside the cell, at the top. As we look at this, we see that on the top there's a greater concentration of sodium and also of calcium on the outside of the cell. What the cells is trying to do is pump calcium from the inside to the outside. Why do cells want to do that? Well, for a very important reason. Calcium must be very tightly controlled in terms of concentration within cells. The reason that that has to happen is because calcium, in high concentrations will cause chromosomes to precipitate, so the calcium concentration must be very, very carefully controlled. One of the ways it's controlled is by a system such as you see on the screen. Well this system doesn't use ATP to move calcium out; instead it uses the high concentration of sodium to move calcium out. You can actually see this happening in this process. And the left of the green wheels that you see there, calcium has bound and you see a sodium that is moving into the other side of the chamber. That happens because sodium is at high concentration and really would like to move into the cell. So the sodium gradient is actually driving calcium to move out. We can see that process happening here. Here's the calcium loading, here's the sodium coming in, and the pressure coming in for the sodium ions moving across the chamber, causes the wheel to turn. As the wheel turns, sodium flows in, in the direction it wants to flow anyway, and calcium is expelled out.

    02:19 Now, no ATP was involved in this and the driving force was the concentration of sodium on the outside compared to the inside. The greater that difference is, the stronger this process can occur. Well, of course the greater this difference is, is a function of the sodium- potassium ATPase. So the sodium-potassium ATPase is doing a lot of things. It's helping to maintain nerve signals, it's helping to maintain osmotic balance, and you can see here, it's helping to move ions across the lipid bilayer.

    About the Lecture

    The lecture Active Transport: Sodium-calcium Exchanger – Biological Membranes by Kevin Ahern, PhD is from the course Biochemistry: Basics.

    Included Quiz Questions

    1. The concentration gradient of one ion can be used to power the transport of a substance into or out of the cell.
    2. It always requires ATP.
    3. It never requires a protein.
    4. It is only involved in moving molecules into cells.
    5. It only moves Na+ or K+ ions into or out of the cell.

    Author of lecture Active Transport: Sodium-calcium Exchanger – Biological Membranes

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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