Practice - Membrane Transport 1 - Online Tutor, Practice Problems & Exam Prep

The NaK ATPase pump transports 3 sodium ions out and 2 potassium ions in, consuming 1 ATP, creating a net positive charge outside the cell. Water movement is facilitated by aquaporins, essential for life due to their rapid transport capabilities. Glucose enters the cell via sodium-glucose symport, utilizing the sodium gradient established by NaK ATPase. This process allows glucose to move against its concentration gradient into the cell and then exit into the blood through facilitated diffusion. Membrane fusion processes like endocytosis and exocytosis differ from glucose transport, which does not require fusion.

Practice - Membrane Transport 1

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 k_t is analogous to K_M from enzyme kinetics, the Michaelis-Menten model. And similarly, lowercase k_d is analogous to lowercase k_cat. Alright. Looking at question 33. In one catalytic cycle, Na⁺K⁺ ATPase transports 3 sodium ions out, 2 potassium ions 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, specifically, a pump, located at the membrane and it pumps out 3 sodium ions and then brings in 2 potassium ions. And this actually creates, 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 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 they are 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 faster.

Moving on now to question 35. Glucose transport from the small intestine lumen to the blood uses a sodium-glucose symport. 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 symport. That's going to 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 Na⁺K⁺ ATPase, right? That is going to be pumping out sodium and bringing in potassium. God, this turned into a mess inside the cell. I have to delete the nucleus. There we go.

Moving on to question 36, a process not involved in the fusion of two membranes or two 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 thought of as cellular drinking. Exocytosis is like cellular vomiting, kind of. It's a vesicle fusing with the membrane and spilling its contents outward. And the entry of enveloped viruses into the cell, the virus as it moves into the cell, it will actually pinch in some membrane with it. And reproductive budding in yeast also involves fusion. Alright. Let's turn the page.

Here’s what students ask on this topic:

What is the role of the NaK ATPase pump in maintaining cellular homeostasis?

The NaK ATPase pump is crucial for maintaining cellular homeostasis by regulating ion gradients across the cell membrane. It actively transports 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell, consuming 1 ATP in the process. This creates a net positive charge outside the cell and a net negative charge inside. The resulting electrochemical gradient is essential for various cellular functions, including maintaining osmotic balance, generating action potentials in neurons, and driving secondary active transport processes like the sodium-glucose symport.

How do aquaporins facilitate water movement across the cell membrane?

Aquaporins are specialized channel proteins that facilitate the rapid movement of water molecules across the cell membrane. While water can diffuse through the lipid bilayer by simple diffusion, the rate is insufficient to meet the needs of living cells. Aquaporins selectively allow water to pass through, significantly increasing the rate of water transport. This is essential for maintaining cellular hydration, regulating osmotic pressure, and supporting various physiological processes such as kidney function and plant water uptake.

How does glucose enter the cell from the small intestine lumen?

Glucose enters the cell from the small intestine lumen via a sodium-glucose symport mechanism. This process utilizes the sodium gradient established by the NaK ATPase pump, which maintains a high concentration of Na⁺ outside the cell and a low concentration inside. The symport protein simultaneously transports Na⁺ and glucose into the cell, allowing glucose to move against its concentration gradient. Once inside the cell, glucose can exit into the blood through facilitated diffusion, moving down its concentration gradient.

What are the differences between endocytosis, exocytosis, and glucose transport?

Endocytosis and exocytosis are processes involving membrane fusion. Endocytosis is the inward pinching of the membrane to engulf extracellular material, often described as cellular drinking. Exocytosis is the fusion of vesicles with the membrane to release their contents outside the cell, akin to cellular vomiting. In contrast, glucose transport does not involve membrane fusion. Glucose enters the cell via facilitated diffusion or symport mechanisms, moving through specific transport proteins without the need for membrane fusion events.

Why are aquaporins essential for life?

Aquaporins are essential for life because they enable the rapid transport of water across cell membranes, which is crucial for maintaining cellular hydration and osmotic balance. While water can diffuse through the lipid bilayer, the rate is too slow to meet the physiological demands of living organisms. Aquaporins ensure that sufficient water can move in and out of cells to support vital processes such as nutrient absorption, waste removal, and temperature regulation. Their role is particularly important in organs like the kidneys, where efficient water reabsorption is necessary for maintaining body fluid balance.