Membrane Transport 1 - Video Tutorials & Practice Problems
On a tight schedule?
Get a 10 bullets summary of the topic
concept
Membrane Transport 1
Video duration:
8m
Play a video:
Video transcript
There are variety of ways that membrane transport can be accomplished and the simplest among these is simple diffusion which only occurs with non polar compounds because they must enter the non polar environment of the membrane. However, it's worth noting that water is a major exception here as it is a very polar molecule. However, it's small enough that it can still cross the membrane through simple diffusion. Facilitated fusion uses channels and carriers that have specificity for particular solute. Now, it is worth noting that water actually moves via facilitated diffusion as well as simple diffusion. And it's moved through channels called aquaporins. And this is because even though water can move via facilitated diffusion, it doesn't actually move fast enough for, the various biological processes that necessitate water crossing the membrane. So it actually also moves through these channels called aquaporins and here we have an example of a protein channel and the basic idea of a channel is it just carries molecules in one direction. And it is basically just, like an open tube in the membrane. So molecules, will just go through the channel. Some channels are gated, so they can have a gating mechanism, something to close off the channel. To carry just one type of solute. However, because they do carry solutes, water tends to move in conjunction with the solute of interest through the channel. Oftentimes, these are ions that are moving through and so water will associate with the ions and they'll all move through the channel together. That said, aquaporins are channels that specifically bring in water and not other stuff. Now, in addition to channels, there are also these carriers and carriers will move will move substances across the membrane and they can actually go in both directions. However, they because this is a facilitated diffusion process, they only move solutes down their concentration gradient. So a nice example of this is glucose transporter and glucose transporter, while it can transport, glucose in both directions, it tends to only move it in one direction down its concentration gradient. And in a very clever way, cells sort of trick the concentration gradient to ensure that glucose through this transporter is always moving into the cell and the way it does that is, whenever glucose enters the cell, it's actually very quickly converted to glucose 6 phosphate that you see right here. So because glucose is converted to this other molecule that maintains a low internal glucose concentration and a higher external glucose concentration because technically, the glucose in the cell is actually glucose 6 phosphate which is a we're going to talk about at length later when we talk about cellular respiration. So, the basic idea here is that these carriers also use facilitated diffusion to move molecules across the membrane. However, the these carriers can actually move the molecules electrochemical gradient of the solute. Now, these, simple diffusion and facilitated diffusion represent forms of passive transport, meaning that no energy is required for this transport to occur. It happens passively. The opposite being active transport, which requires energy. And actually, there's 2 types of active transport. There is primary active transport, which directly uses ATP to move solutes against their concentration gradients. And generally, these are found as pumps. And pumps, play a big role in maintaining specific electro chemical gradients across the membrane which is really important in neuroscience and also really important for cellular respiration and and something again we're going to talk about at great length. So, two really good examples of these primary active transporters, specifically pumps are the sodium potassium pump also called NaK ATPase occasionally. And these pumps move, the ions, sodium and potassium across the membrane. They pump out, they pump 3 sodiums and 2 potassiums at the expense of you can see one ATP right there. Another really good example of a pump is, these pumps that we're going to take a look at later in cellular respiration and these are proton pumps and they play a crucial role in ATP synthesis. So, due to the electron transport chain, these pumps will actually pump hydrogen ions into the, the intermembrane space of the mitochondria. And then this, this electrochemical gradient that is created, which is also called the proton motive force, This electrical chemical gradient will drive, ATP synthase, which is an enzyme that produces ATP from ADP and inorganic phosphate, as it transports hydrogen ions or protons down their electrochemical gradient. So, passive transport does not use energy and passive transport comes in the form of simple diffusion and facilitated diffusion and primary active transport uses energy directly in the form of ATP. Now, let's turn the page and talk about secondary active transport.