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11. Biological Membranes and Transport

1

Passive Membrane Transport

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So now that we've differentiated between passive and active membrane transport in this video, we're going to talk more details about passive membrane transport. And so if we take a look at our membrane transport map over here, what you'll notice is that passive transport can be further categorized into simple, passive transport or simple diffusion and facilitated passive transport or facilitated diffusion. And really, that's the main focus of this video that there are two types of passive transport, simple and facilitated passive transport. And so the first type, the simple passive transport or simple diffusion, is as simple as it sounds. Simple diffusion is going to be non energetic, simple and direct diffusion straight through the membrane. And this means that the molecules are going to be squeezing between the Foss full lipids in order to defuse from an area of high concentration down to an area of low concentration. Now, the second type of passive transport here, the facilitated passive transport or facilitated diffusion again is also going to be non energetic because it is passive and we know passive means no energy, and so this is non energetic diffusion that is facilitated by a membrane transport protein. However, again, the membrane transport protein does not utilize a teepee or energy, since it's non energetic and so down below. In our example, uh, here we can differentiate between the two different types of passive transport. Simple, passive transport versus facilitated, passive transport or diffusion. And so over here, on the left hand side of this image, what we're showing you is simple diffusion. And really, what you can see is that the molecules are gonna be transported across a biological membrane from an area of high concentration to an area of low concentration. But because it's simple, it does not require facilitation from a protein. So these molecules are able to squeeze their way between the fossa lipids, just as we mentioned up above to get to the other side of the membrane. And so molecules that are capable of simple diffusion are going to be very, very small and very non polar molecules such as the gasses, carbon dioxide, oxygen and nitrogen gas. Now, on the other hand, over here on this side of our image, what we have is facilitated passive transport or facilitated diffusion, and so notice that the molecules are still being transported from an area of high concentration down to an area of low concentration, so still no energy is needed. This is still non energetic, however, which will notice is different is that there is this membrane protein here that is required to facilitate the diffusion. And so what you'll notice here is that we have molecules here that are charged, and we know that charged molecules can't really cross a membrane without facilitation. However, if they do have facilitation, they are able to be transported passively down their concentration ingredient, just as we see here. And that is what we're calling facilitated diffusion. And so this here concludes our video, distinguishing the two different types of passive membrane transport, which are simple and facilitated passive transport. And so we'll be able to get some practice applying these concepts in our next few videos, so I'll see you guys there.

2

Problem

The difference between simple and facilitated diffusion is that facilitated diffusion:

A

Requires a protein transporter.

B

Moves molecules against their concentration gradient.

C

Requires energy.

D

Freely diffuses molecules against their concentration gradient.

3

Problem

Simple diffusion and facilitated diffusion across a membrane both ___________________:

A

Move molecules against their concentration gradient.

B

Move molecules with their concentration gradient.

C

Require ATP.

D

Use a protein transporter.

E

Transport charged molecules from low to high concentration.

F

Transport large, charged molecules from high to low concentration.

G

Both b and f are true.

4

Passive Membrane Transport

7m

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Okay, So now that we've differentiated between the two different types of passive membrane transport, simple diffusion and facilitated diffusion and this video, we're going to talk a little bit about the kinetics of passive transport, which is going to help us even further distinguish between simple diffusion and facilitated diffusion. As we'll see now, you might recall that way back in our previous lesson videos, we actually covered enzyme kinetics and from those old videos on enzyme kinetics, we already know that kinetics is just the field that studies the rates, velocities and speeds of particular processes. And so the rate or velocity of passive transport is driven by the extent of the concentration Grady int across the membrane. And so the greater the concentration is of the defusing substance on one side of the membrane, the faster the rate of simple the fusion. And so, of course, what this means is that the rate of simple diffusion will form linear data when plotted onto a graph like what we have down below right over here. And so this graph should look familiar to you guys because it's the same exact graph from our old lesson videos on enzyme kinetics and so on the Y axis. What we have is V not which is the initial reaction velocity. And of course, the reaction here in this scenario is just diffusion. And so v not is just the initial velocity of diffusion. And on the X axis, what we have is the substrate concentration in quotes because technically, it's not a substrate if diffusion is the only thing that's occurring, But really you can just think of the substrate, concentration and quotes here as just the concentration of the defusing substance. And so right now we're just focusing on this green line right here for simple diffusion. And the most important thing that you should take away here from this Green line is that simple diffusion will form linear data when plotted onto this graph. And so, as we increase the concentration of the defusing substance from left to right, we will also increase the rate or the velocity of simple diffusion in the same manner. And that's what creates this linear data that we see right here. And that's exactly what we said up above right here. The greater the concentration, the faster the rate of simple diffusion forming linear data. And so, of course, because linear data is associated with simple diffusion, uh, this means that the data is explained by the equation of a line which recall is just why equals M X plus B and so so far, this is pretty easy. Pretty straightforward. Simple diffusion forms a linear straight line now, in terms of the rate of facilitated diffusion. On the other hand, you may have already noticed that it's a little bit different by looking at this blue curve that we have here. And so one of the first differences you probably noticed is that simple diffusion forms a straight linear line, whereas facilitated diffusion forms this curve. But another thing that you should notice is that the rate of facilitated diffusion is even faster than the rate of simple diffusion at any concentration of defusing substance. And so, no matter what value of concentration of defusing substance, you choose here if you go up and look at the velocity levels that correspond with them. What you'll notice is that the rate of facilitated diffusion is always faster than the rate of simple diffusion. Now, although the rate of facilitated diffusion is even faster than the rate of simple diffusion. There is one limitation that we should take into account, however, and that is that the rate of facilitated diffusion is limited, and it's limited by the amount of transport protein that's present in the membrane. And so what this means is that ultimately, when we increase the concentration of defusing substance enough, the rate of facilitated diffusion will reach a limitation. A V max, if you will, a maximum rate of diffusion and this maximum rate of diffusion is again limited by the amount of transport protein. And so this limitation here is very similar to how an enzyme catalyzed reaction is limited by the amount of enzyme. And so you can really think of the transport protein that's involved and facilitated diffusion as being very similar to an enzyme in that respect, in terms of the limitation and so because facilitated diffusion is limited by the amount of transport protein. Therefore, what this means is that passive facilitated diffusion rates. Instead of forming linear data, they're going to form a hyperbolic Michaelis Menton type curve. And so that's exactly why we have this curve right here for facilitated diffusion approaching some kind of maximum velocity that's limiting it. And again, that's limited by the amount of transport protein. And so the biggest take away here is that facilitated diffusion is going to be hyperbolic form, hyperbolic data, whereas simple diffusion will form linear data. And so, of course, this hyperbolic curve right here the data is explained through the McHale is meant in equation, which is what we have right here. And so really, the only difference here is that we have Katie are instead of the meticulous, constant K M that we're used to seeing in our enzyme kinetics. But really, the K T. R is pretty much the same exact thing. It's analogous to the K M. And so the K TR would represent the substrate concentration at which the transport protein is half saturated and so you can see that the TR and transport reminds us that it's going to be for the diffusion and the transport of ah, a specific molecule. And so again, the biggest takeaways that you guys should get from this video is that simply by plotting the data onto a graph like this, a biochemist can tell if a molecule is diffusing via facilitation. because it will form a hyperbolic McHale is meant in curve or if the molecule is diffusing by simple diffusion because it forms linear data that's explained by the equation of a line, and so that will help us differentiate between facilitated and simple diffusion even more. And that concludes our lesson on the kinetics of passive transport, and we'll be able to get some practice applying these concepts and our next couple of videos, so I'll see you guys there.

5

Problem

The rate of movement (flux) of a substance X into cells was measured at different concentrations of X to construct the following graph. Does the graph’s data suggest diffusion of X into cells is mediated by a protein transporter?

A

Yes, diffusion of X is mediated by a protein transporter (facilitated diffusion).

B

No, diffusion of X is not mediated by a protein transporter (simple diffusion).

6

Problem

The rate of transfer across a membrane is measured for a given molecule. The diffusion rate is seen to be hyperbolic with respect to the concentration of the diffusing molecule. The method of transport is which of the following?

A

Facilitated diffusion.

B

Active transport.

C

Simple Diffusion.

D

Symporter diffusion.

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