by Thad Wilson, PhD

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    00:01 The next one we’re going to go through is our ATPases.

    00:04 The prototype that we’re going to use for this is a V-type calcium or V-type sodium-potassium ATPase or a pump.

    00:13 Now, why are these pumps so important? Well, this is important because the last two things we went through, pores and ion channels, needed to have a concentration gradient for there to be any transport across the membrane.

    00:27 Here, we are creating the gradient or we are pumping against the gradient.

    00:33 So we don’t need to rely on a gradient, we can do it ourselves by using energy to get us across that particular cell membrane.

    00:42 So that’s why this is called active transport.

    00:45 And this is used to either establish a gradient or move something against other gradient.

    00:53 Okay, besides having ATPases in places like the plasma membrane, we can also use ATPases in other places such as the endoplasmic reticulum.

    01:04 There’s a certain kind of calcium pump located on the endoplasmic reticulum of muscle cells that allows us to pump in calcium.

    01:14 And why this is so important is this is going to help us relax a muscle by removing calcium from the cytosol of that muscle cell.

    01:24 Now, what are the important aspects of having these particular ATPases? Well, the first thing to think about is there needs to be ATP hydrolysis occur.

    01:35 Now, this occurs both on our pumps, as well as on our ABC transporters and these are not pumps in themselves but still require ATP hydrolysis or energy to cause the transport process to work.

    01:52 But let’s get back to our prototype.

    01:55 Usually, for our prototype, what we’re trying to do is pump a certain number of ions across the cell.

    02:03 For this sodium-potassium ATPase, we’re going to be pumping an unequal number across the membrane.

    02:10 So, three get kicked out of the cell and two potassium move into the cell.

    02:15 This unequal number though creates an electrogenic response, which means that there’s going to be an electrical gradient formed.

    02:25 Because you’re losing three positives and gaining two positives, that means there’s a positive difference there.

    02:31 As that difference occurs, you’re going to create an electrical gradient.

    02:35 So let’s go through that prototype in more detail.

    02:38 There’s a number of cyclical processes involved here and we’re going to take these one by one to explain to you how this process works.

    02:49 The first thing we’re going to talk about is to think about the number of different ions that are exchanged.

    02:55 So this, again, is a V-type pump, extrudes or pushes out three sodium and brings in two potassium.

    03:03 The the other things to think about is where this is primarily located.

    03:07 Usually, this is going to be on the basolateral side of most epithelial cells, and we’ll keep talking about epithelial cells throughout this particular course.

    03:18 But these cells are usually located along on a junction in which you’re moving something from one side of that cell across one membrane into the cytosol then across that membrane on the other side to be moved into somewhere like the blood.

    03:36 It involves a number of steps in which here have eight and we’ll try to animate these for you so you really understand how this sodium-potassium ATPase works.

    03:48 Okay. Now, that we have the basics of the sodium-potassium ATPase down, let’s now take each one of those steps in turn.

    03:56 So let’s first start off with the basic portion of the pump.

    04:00 So we have ATP bound to it, we have the outer gate closed, and we have nothing in the pump yet.

    04:10 We now have sodium that enters into the pump, in fact, three sodium to be precise.

    04:19 The next thing that happens is the hydrolysis of ATP.

    04:22 Hydrolysis means we break down ATP into an ADP and an inorganic phosphate.

    04:28 The inorganic phosphate stays bound.

    04:31 What this also does is close the inner gate.

    04:40 Now, the outer gate opens through a conformational change and that allows sodium to leave.

    04:50 This then allows the potassium, in fact, two of them to be precise, entering into the pump.

    05:05 Then, inorganic phosphate leaves the pump, closing the outer door.

    05:12 And now, ATP binds back to the pump which opens up that inner gate, allowing potassium to go into the cell.

    05:25 And that sets up the sodium-potassium ATPase pump cycle, where you need to have ATP bound, broken down, sodium entering, sodium to and exit the cell, potassium to enter the pump, and then, finally, potassium to enter the cell.

    05:43 And it’s very important to have that process working correctly to open and close the various gates at the appropriate time.

    05:51 It’s a great example of a sodium-potassium ATPase V-type pump.

    About the Lecture

    The lecture ATPases by Thad Wilson, PhD is from the course Membrane Physiology.

    Included Quiz Questions

    1. P-type
    2. V-type
    3. F-type
    4. ABC-type
    5. Passive Pore
    1. Inner gate opening
    2. Outer gate opening
    3. Sodium entry
    4. Sodium excitation
    5. Potassium release to the outside of the cell
    1. They use energy to create a gradient
    2. They undergo a conformational shape change
    3. They are bigger
    4. They don't produce an electrochemical gradient
    5. They exchange cations
    1. Energy is used to pump a substance across the cell membrane against a gradient.
    2. Energy is used to create a gradient.
    3. Energy is not necessary to create a gradient.
    4. A negative gradient is created.
    5. Ions are transported following their own gradient.
    1. …calcium into the endoplasmic reticulum away from the cytosol.
    2. sodium into the endoplasmic reticulum away from the cytosol.
    3. calcium out of the endoplasmic reticulum and into the cytosol.
    4. sodium out of the cell membrane.
    5. potassium into the cytosol.
    1. …three Na+ outside the cell and two K+ inside the cell.
    2. ...two Na+ outside the cell and two K+ inside the cell.
    3. ...three Na+ inside the cell and two K+ outside the cell.
    4. ...two Na+ inside the cell and two K+ outside the cell.
    5. ...four Na+ inside the cell and two K+ outside the cell.
    1. To create an electrogenic gradient
    2. To remove positive charges from the inside of the cell
    3. To remove negative charges from the outside of the cell
    4. To restore electrogenic balance
    5. To facilitate passive entry of water following sodium
    1. In the basolateral side of the cell membrane
    2. In the apical side of the cell membrane
    3. In the basal side of the cell membrane
    4. At the luminal side of tight junctions
    5. At the luminal side of gap junctions
    1. Three Sodium molecules enter the pump from the inside of the cell
    2. Three Sodium molecules enter the pump from the outside of the cell
    3. Two Potassium molecules enter the pump from the inside of the cell
    4. Three Potassium molecules enter the pump from the outside of the cell
    5. Two Sodium molecules enter the pump from the outside of the cell
    1. The hydrolysis of ATP
    2. Inorganic phosphate leaving the pump
    3. ATP binds to the pump
    4. Organic phosphate leaving the pump
    5. ADP binds to the pump

    Author of lecture ATPases

     Thad Wilson, PhD

    Thad Wilson, PhD

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    need to be more clear
    By rene p. on 16. September 2017 for ATPases

    somethings said are not so clear eventhough we can refer books............... In the quiz the na+ k+ atp ase is said to be p type pump..................... but in the lecture it says it is a v type pump........................ i want to know which is right..............................