So now that we've covered secondary active transport, in this video, we're going to talk about a specific example of secondary active transport, and that is the glucose active symporter model. Now, this is a classic and relevant example of secondary active transport. And more specifically, we're going to be looking at the intestinal epithelial sodium glucose symporters. And so just to get a better idea of exactly what we're talking about when we refer to intestinal epithelial cells, let's take a look at our image down below. And so notice that we've got our anatomical figure over here and we're zooming into this specific region. And, you can see that we have the stomach, the pancreas, and the intestinal lumen right here. And so if we zoom into the intestinal lumen wall right here in this region, what you'll notice is that the wall is made up of these villi structures that you see right here, these curved structures that give more surface area to the intestinal lumen and allow for better absorption of materials that we eat. And so what you'll notice is that these villi are lined with individual intestinal epithelial cells. And also these villi are closely associated with our bloodstreams, which we have right here in the villi. And so if we zoom into this particular region over here on the right-hand side of our villi, notice that, again, zooming in will show a bunch of individual intestinal epithelial cells. And these little structures that you see here would be the microvilli. Again, allowing cells to increase surface area and increase their absorption of materials that get into our intestines. And so notice that now we're zooming into one individual intestinal epithelial cell here, and that is going to be this image that you see down below. And so really, this image down below is the main image for this lesson, and all of the other images are just there to give you guys a little bit of context. 3 important components that you guys should know. And we've labeled each of these three components as a, b, and c, and you'll be able to see each of these 3 components corresponds with the images that we have down below. So you can see component a is right here, component b is over here, and component c is right here. And so, of course, we know from our previous lesson videos that secondary active transport is indirectly driven by primary active transport. And so that's exactly where we start with component a is primary active transport. And more specifically, it's actually the sodium potassium pump that is going to maintain a transmembrane sodium gradient. And this transmembrane sodium gradient, we know is going to be really high on the outside of the cell, and really low on the inside of the cell. And so if we take a look at our image down below at component a over here, notice that it's just the sodium potassium pump that we talked about from our previous lesson videos. And so we know that it hydrolyzes ATP, and in the process, it transports 3 sodium ions to the outside of the cell as it transports 2 potassium ions to the inside of the cell. And so again, this is establishing a concentration gradient for sodium that is really high on the outside of the cell and really low sodium on the inside of the cell. And so that transitions us directly into the secondary active transport part of this lesson, and that is exactly where the sodium glucose symporters come into play. And so the sodium glucose symporters are going to co-transport, as their name implies, sodium and glucose in the same direction across the membrane. And that's what makes them symporters because the 2 molecules are being transported in the same direction. And so really, what powers the transport of this co-transport here is that there are 2 sodium ions that are going to be imported down their concentration gradients or with their concentration gradients from high to low. And, these 2 sodium ions being imported down their concentration gradients is really what powers the movement of 1 glucose molecule being imported into the cell against its concentration gradient from an area of low concentration to an area of higher concentration. And so if we take a look down below at our image, notice that we have component b up here at the top right, and this is our sodium glucose symporter, our secondary active transporter model. And so notice that no ATP hydrolysis is directly involved here with this, sodium glucose importer. So we know it's gotta be a form of secondary active transport, and it's utilizing the gradient that was established by the sodium potassium pump, the sodium gradient that was established. So there's low sodium on the inside and high sodium on the outside. And so as sodium gets imported down its concentration gradient from high to low, it's powering the movement of glucose from the intestinal tract into the intestinal epithelial cell against its concentration gradient. And so now that transitions us to the last part here of our lesson, part c. And that is just to know that as glucose is pumped into the intestinal epithelial cell from the intestinal tract to the inside of the cell, it's also simultaneously being moved into the bloodstream via a GLUT2 uniporter. And of course, we know uniporters will transport 1 molecule in one direction across the membrane, and that is going to be glucose. And so if we take a look at our image down below, notice down below part c here, we have the GLUT2 uniporter, which is going to transport glucose, in one direction across the membrane so that it can diffuse into the blood. And of course, once glucose is in the blood, that glucose can diffuse to pretty much every cell in our bodies. And so one thing to note here is that the sodium glucose symporter that we talked about in part b and this, GLUT2 uniporter that we just talked about in part c are actually operating on opposite sides of the intestinal epithelial cells. And so if we take a look back down below, notice again that the sodium glucose importer is operating on the intestinal tract, side of the cell. And notice that the GLUT2 uniporter is operating on the opposite side of the cell that's closer to the bloodstream. And so all of these systems here are operating together to allow glucose that gets into our digestive system when we eat foods and transport that glucose from our intestinal tract into our intestinal epithelial cells, and then through, the intestinal epithelial cell into the blood where, again, it can be transported to every cell in our bodies. And so really, it's this sodium glucose importer here that is our example of secondary active transport. And really, this is the conclusion of our lesson on glucose active importer model, and we'll be able to get a bunch of practice in our next couple of videos. So I'll see you guys there.
Glucose Active Symporter Model - Online Tutor, Practice Problems & Exam Prep
Glucose Active Symporter Model
Video transcript
The Na+-Glucose symporter transports the two molecules into the cell, while the Na+-K+ ATPase uses ATP to transport Na+ ions out of the cell. What would be the result of a mutation leading to a nonfunctional Na+-Glucose symporter?
Imagine that you perform a series of experiments to test the rate of glucose transport (V0) into epithelial cells using the Na+-Glucose symporters. These experimental epithelial cells contain no intracellular Na+ but have the same glucose concentration as their surroundings. In experiment #1, you transfer your cells to test tubes that contain different extracellular [Na+] & then measure the rate of glucose transport (V0). In experiment #2, you introduce leakage Na+ channels into the cell membranes & then repeat the same experiment. Label the data on the plot below as showing results to either Experiment #1 or Experiment #2.