10. Lipids
Physical Properties of Biological Membranes
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Physical Properties of Biological Membranes
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in this video, we're going to begin our lesson on the physical properties of biological membranes, and we're going to start off by talking about lateral and trans verse diffusion. And so really, there are two main types of lipid diffusion that described the fluid like motion of lipids within a bi layer. And so the first type of lipid diffusion is going to be lateral diffusion. And so lateral diffusion, as its name implies, is gonna be an uncapped, ill ized lateral movement of lipids. And of course, lateral just means side to side. And so the lipids and lateral diffusion are going to always remain along the same sheet of the lipid by layer. And although this is an uncapped allies process, it's still an extremely fast process. And so, if we take a look at our image down below over here on the left hand side, notice that we're showing you lateral diffusion, and we're focusing specifically on this fast. Whoa lipid right here. And so lateral of course means side to side. And so this fossil lipid is capable of diffusing both to the left and to the right here. We're showing it diffused to the right to this position right here and so lateral diffusion. The side to side diffusion along the same by layer sheet is an incredibly fast process, even though it's an uncapped ELISA process. Now the second type of lipid diffusion is going to be trans verse diffusion, otherwise known as flip flop diffusion. And so trans verse or flip flop diffusion is going to be a catalyzed process, unlike the previous lateral diffusion, which was an uncapped allies process. And this will transfer lipids across to the opposite sheet of the lipid bi layer instead of keeping the lipid on the same sheet of the lipid bi layer like lateral diffusion did. Now, if there is not an enzyme present, then trans verse diffusion is going to be an extremely slow process. And this could be so slow that it could take days without an enzyme. And so really, an enzyme is required for this to occur, and it must be a catalyzed process to occur at a significant enough rate. Now. This slow right that occurs without enzyme is what allows the inner and the outer sheets of a biological membrane to maintain different lipid compositions. And so if we take a look at the right side of our image down below, notice that we're showing you trans verse or flip flop diffusion and noticed that we're focusing on this fossil lipid molecule right here. And notice that in trans verse diffusion, it's defusing across to the opposite by layer sheet and notice that it ends up here in this position in this opposite by layer sheet. By the end and without an enzyme, as we mentioned up above, it could take days. And so it's an incredibly slow, slow process. If there is no enzyme involved and so moving forward, we're going to talk about what specific enzymes allow trans verse or flip flop diffusion to occur at a significant rate. So I'll see you guys in our next video.
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Physical Properties of Biological Membranes
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So from our last lesson video, we already know that trans verse diffusion is an extremely slow process. And so, in order for trans verse diffusion to occur at a reasonably fast rate, it's going to require an enzyme to catalyze the process. And so in this video, we're going to talk about the enzymes that catalyze trans verse diffusion. And so really, there are three main types of membrane embedded enzymes that catalyzed trans verse diffusion. And so we've got those three enzymes number down below now. One thing to note is that these first two enzymes require energy in the form of ATP in order to catalyze trans verse diffusion. Whereas this last enzyme down here actually does not require ATP, so no ATP is required to catalyze trans verse diffusion. Now, the very first enzyme that we have here on this list is going to be the flip hace. Now. The flip pace, as its name implies with the flip, is going to flip very specific lipids from the outer sheet of the membrane to the inner sheet of the biological membranes. Now what helps me remember that flip paces will flip lipids from the outer sheet to the inner sheet and not vice versa, is that I correspond the eye with the flip with the I N N er, and so that helps remind me that the lipids final position is going to be in the inner sheet because of the I. And so that reminds me that flip paces flip lipids from the outer sheet to the inner sheet of the biological membranes. Now the next ends I'm that we have here is the opposite of the flip pace, which is the flop pace. And so the floppies, as its name implies, is going to flop lipids from the inner sheet to the outer sheet of the biological membrane. And so again, what helps me remember that flop paces will flop lipids from the inner to the outer sheet is I correspond the O and the flop pace with the oh and outer, and that reminds me that the lipids final position is going to be in the outer sheet, and so flop paces will flop lipids from the inner to the outer sheet. Now, the last enzyme that we have on this list is the scram Blace, and so the scramble is as its name implies, is going to scramble the lipids in either direction. So it scrambles them essentially in both directions, across the lipid bi layer, specifically down the concentration ingredient. And because the lipids are again moving down their concentration, Grady INTs it does not require ATP for them to flow down the concentration Grady INTs. And so, if we take a look at our image down below, notice that we've got the three different enzymes here on the far left, we have the flip HACE, which, of course, is going to flip the fossil lipid from the outer sheet to the inner sheet of the biological membranes. And so notice that the outer sheet is labeled as this top sheet here, and the inner sheet is labeled as this bottom sheet down here, and so notice that the flip pace does require a teepee energy in the form of a teepee in order to catalyze this process. Now, the next one that we have is the flop pace, which of course, is going to do the opposite of the flip pace and flop the fossil lipid from the inner sheet to the outer sheet, which is the final position and again. It's going to use energy in the form of ATP to catalyze that process. And then last but not least, what we have is the scram Blace here, and the scramble is notice. It's going to flip the fossil lipids and flop the, uh, fossil lipids, Uh, and both directions here. And so it's going to transport lipids down their concentration Grady int, which is why no ATP is required for this process. And so, if you think about this for a moment, notice that both the flip pace and the floppies are gonna help create diversity between these two different sheets of the biological membrane, whereas the scramble is is really going to eliminate the diversity between these two different sheets. And so by controlling the expression of what specific enzymes are going to be in the membrane, a cell can control the composition and the diversity between its outer and its inner biological membranes sheets. And so this here concludes our introduction to the enzymes that catalyze trans verse diffusion, and we'll be able to get some practice applying these concepts as we move forward. So I'll see you guys in our next video
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Physical Properties of Biological Membranes
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In this video, we're going to introduce the transition temperature of lipid bi layers, and so the transition temperature is also commonly referred to as the melting temperature and is abbreviated as the T M. And so this is the specific temperature where a membrane will either lose or gain. It's fluid ity, depending on if the temperature is above or below the transition or melting temperature. And so at temperatures above the TM, membranes are going to transition from having a thick gel like viscosity toe having a very fluid like viscosity. And so it's important to note that the more fluid like the membrane is, the more permeable the membrane will also be. And so the more permeable, the the easier it is for substances to cross or penetrate through the membrane. And so if we take a look at our image down here on the left hand side, notice that we're showing you this graph where we have the membranes, fluid ity on the Y axis and the temperature on the X axis increasing from left to right and notice that we have the specific transition or melting temperature Mark. Here is the TM, which is corresponding with a very unique position on this graph, where the membrane is either losing or gaining its fluidity again, depending on if the temperature is above or below the TM at temperatures below the TM Over here on this part of the x axis, notice that the membrane takes on a very gel like viscous and rigid structure, like what we see here and this gel like structure is going to be less permeable. And so substances that used to be able to easily cross to the memory are gonna have a much harder time crossing the membrane. Uh, if the membrane is gel like and less permeable and of course, at temperatures above the TM over here on this part of the X axis, notice that it corresponds with a membrane fluidity that is very fluid like like the ones that we see here, and so notice that the membranes are much more separated and much more permeable. And so this will allow substances to cross through the membrane much, much easier. Now it's important to note that these membrane transition temperatures, like the ones that we see right here, are primarily dictated by the same exact two factors that affect the fatty acids melting point and recall. We talked about ah fatty acids melting point much earlier in our lesson and so down below right here in this box, notice that we have the two primary factors that affect the temperature, the melting or transition temperature. And again, these two primary factors are the same two factors that affect the fatty acids melting point. So we already are familiar with these two factors. The first is the length of the chains of the fossil lipids. And so the longer those hydrocarbon chains are, the higher the transition temperature or the melting temperature will be. And of course, the second primary factor is going to be the degree of saturation or the amount of double bonds present in the hydrocarbon chains of the fossil lipids. So the more double bonds that air present, the lower the melting or transition temperature will be Now. It's also important to recall that when it comes to a biological membrane that there are other molecules that can also affect the fluidity of the membrane, such as proteins or cholesterol, which we know is also embedded in the membrane. So we cannot forget about these other molecules as well. That can also help to affect the fluidity, the fluidity of the membrane and the permeability of the membrane. And so cells are actually able to control the fluidity of their membrane and the permeability of their membrane by affecting these two primary factors, as well as by affecting the other molecules that are embedded in the molecules in the membrane. And so this year concludes our introduction to the transition temperature of lipid bi layers, and we'll be able to apply the concepts that we've learned here in our next video, so I'll see you guys there.
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Problem
ProblemThe fluidity of a bilayer is generally increased by:
a) The binding of water to the fatty acyl side chains.
b) An increase in fatty acid chain length.
c) An increase in the number of double bonds in the fatty acid hydrocarbon chains.
d) A decrease in temperature.
A
The binding of water to the fatty acyl side chains.
B
An increase in fatty acid chain length.
C
An increase in the number of double bonds in the fatty acid hydrocarbon chains.
D
A decrease in temperature.
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Problem
ProblemWhich of the following would increase the transition temperature of a membrane?
a) A decrease in the fatty acid tail length.
b) An increase in the number of double bonds in the fatty acid chains.
c) Loose packing of fatty acid tails.
d) Free fatty acids in the environment.
e) None of the above would increase the transition temperature.
A
A decrease in the fatty acid tail length.
B
An increase in the number of double bonds in the fatty acid chains.
C
Loose packing of fatty acid tails.
D
Free fatty acids in the environment.
E
None of the above would increase the transition temperature.