Practice - Membrane Transport 1 - Video Tutorials & Practice Problems
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Practice - Membrane Transport 1
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Let's finish up with some membrane transport questions. If you haven't done 32 yet, pause the video now. For the process of solute transport, the constant kt is analogous to Kilometers from enzyme kinetics, the Michaelis Menten model. And similarly, lower case kd is analogous to lower kcat. Alright. Looking at question 33. In one catalytic cycle, NaK ATPase transports 3 sodium out, 2 potassium in, and it has to burn 1 ATP in order to complete this process. So it converts ATP to ADP and inorganic phosphate. Of course, this is a transporter or it's a I mean it's a pump specifically located at the membrane and you pump out 3 sodium molecules and then you bring into potassium I'm sorry, I said molecules, I meant ions. Then you bring in 2 potassium ions. And this actually creates a, essentially a net positive charge outside, a net negative charge inside. And this is due to the fact that even though we're just moving positively charged particles here, we're moving 3 positives out for every 2 we bring in. So that creates an imbalance, positive outside and net in, eventually, you get net positive outside and net negative inside. The movement of water across the membrane is facilitated by proteins specifically channels called aquaporins. And these selectively filter for water. They only allow water to pass through and these are basically, essential to life because while water is capable of moving through the membrane by simple diffusion, it actually, not enough water can pass through the membrane in order to sustain, living processes. So aquaporins are essential for life because they allow water to pass through the membrane much much much faster. Moving on now to question 35. Glucose transport from the small intestine lumen to the blood. Uses a sodium glucose import. And it uses a facilitated diffusion transporter, which is for glucose to be clear. And basically what this looks like if we have our cell here and, you know, this will have like little furry doodads on this side. Here's the blood. Here's the lumen of the intestine. This cell miraculously somehow knows to put on this particular side the glucose import glucose sodium import. That's gonna take glucose and sodium into the cell and this works because in the lumen, you have a high sodium concentration and in the cell you have a low sodium concentration. And you know why you have low sodium concentration in the cell? Because of NaK ATPase, right? That is going to be pumping out sodium bringing in potassium. God, this turned into a mess inside the cell. I have to delete the nucleus. There we go. K There's our ion. Anyhow, that is going to establish this gradient. Right? And so of course out here because all the sodium is getting pumped you're going to have high sodium out here too. So that's why this symport works and it's going to bring glucose into the cell and there's there's a lot of glucose in the cell, right? So that's moving against its concentration gradient. However, because there's a lot of glucose in the cell, glucose can travel into the blood simply through facilitated diffusion. That's because it's moving down its concentration gradient. So, it catches a ride in with sodium and then leaves via its own devices. Moving on to question 36, a process not involved in the fusion of 2 membranes or 2 regions of the same membrane is the entry of glucose into the cell. I mean we just talked about it. It's moving through a channel. This doesn't require any sort of membrane fusion event whereas endocytosis is the, membrane basically pinching inward. It's sort of it's almost thought of as like cellular drinking. Exocytosis is like cellular vomiting kind of. It's, a vesicle, you know, fusing with the membrane and spilling its contents outward. And, entry of, enveloped viruses into the cell, the virus as it moves into the cell, it will actually, pinch pinch in some membrane with it. And reproductive budding in yeast also includes, infusion. Alright. Let's turn the page.