Sodium-potassium Atpase – Protein Functions

by Kevin Ahern, PhD

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    00:00 Now at the cellular level, I’ve been talking so far about the organismal level, the movement of materials through the body, but at the cellular level, proteins play very important roles in transport as well. And this transport system I'm going to show you, is one of the most important one that cells have, and it's one that's found in most cells. Now this transport system is called the sodium-potassium ATPase, and it's what we call a transmembrane ion transport. This is a protein that resides in the lipid bilayer. We can see in the lipid bilayer the green sodium-potassium ATPase. If we start with this on the left, we see that this protein has bound to two atoms of sodium, they are shown inside the Green chamber there, and we see a third one getting ready to enter. After the three have loaded, an ATP molecule is bound by the same sodium-potassium ATPase protein and it cleaves ATP. The cleavage of ATP causes the sodium-potassium ATPase to change shape. And now instead of being opened from below, it's open above. Well below is the inside of the cell and above is outside of the cell. And in the process of having that happen, the three sodiums are released.

    01:23 Now the release of those three sodiums is really important, because sodiums are at higher concentration outside the cell than they are inside the cell. Now as I said the release of the three sodiums into the outer part of the cell is very, very important because, what's happening is the cell has a need to get rid of that sodium as I’ll explain in just a minute. The difficulty that the cell has is the concentration of sodium is higher outside the cell than it is inside the cell. Now what that means is that the cell in pushing the sodium out, is having to fight a gradient. The sodium-potassium ATPase is making that happen and the way it's making it happen is by cleaving ATP. It takes energy to move things from low concentration to high concentration, just like it takes energy to move water uphill.

    02:17 So moving things in this way is equivalent to moving water uphill. Well after the sodium- potassium ATPase has released the three sodiums outside the cell, you can see next, it binds two potassium ions, and the two potassium ions comes into that open chamber that was left previously by the exit of the sodium. The entry of the two potassiums comes in, and you can notice at the bottom of that chamber, that there's a little blue thing. The little blue thing at the bottom of the chamber is a phosphate that was left behind when ATP got cleaved on the previous exchange. On the next step of the process, what happens is that the phosphate is released and the two potassiums come in. Now this allows potassium to also move against a concentration gradient. Now I’ve plotted the gradients on the side of this figure. You can see that for sodium for example, the sodium concentration gets increasing as we go up, and the potassium concentration increases as we go down, meaning therefore that both ions are being moved against a gradient. Now why is this important? Well it is important because cells have to maintain a balance of things, and the balance of things that they have to do is because of osmotic pressure. Osmotic pressure is a difficult thing for cells to manage, and the managing of the osmotic pressure is partly accomplished by this pump. This pump is what I describe to students as the cost of being alive, because to be alive, a cell has to be able to expend energy to keep the osmotic pressure within reasonable distance.

    03:55 With this I’ve concluded four more functions for proteins and as we've seen, the diverse function of proteins spans everything from antibodies protecting the body against infection, to gene expression, to helping cells to make the necessary proteins that they have to make, to transport functions listed as we can see here, that help both cells and organisms to move materials as necessary. The diversity of functions of proteins in the body is remarkable and necessary.

    About the Lecture

    The lecture Sodium-potassium Atpase – Protein Functions by Kevin Ahern, PhD is from the course Biochemistry: Basics.

    Included Quiz Questions

    1. It requires ATP
    2. It is a synport
    3. It uses energy from the sodium gradient to move potassium
    4. It is embedded in the mitochondrial membrane
    1. It exhibits cooperativity in binding to oxygen, but myoglobin does not
    2. It requires ATP to carry oxygen
    3. It saturates with oxygen at low oxygen concentrations
    4. It has a greater affinity for oxygen than myoglobin

    Author of lecture Sodium-potassium Atpase – Protein Functions

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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