Cholesterol and membrane fluidity

[alexamasan]

So does cholesterol increase or decrease membrane fluidity? I've always thought it decreased fluidity because cholesterol fits inside the fluid unsaturated phospholipid fatty acid legs, making them less fluid. My Cliffnotes AP bio says that too.

However, sadly on Chad's last organic chemistry video, he says that cholesterol increases membrane fluidity.

Honestly, I think Chad is the only one I've heard say that cholesterol increases membrane fluidity. I'd hate to say that Chad is wrong, but he might be. What do you guys think?

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[uncbestyet]

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[ataraxia7]

I don't think this is correct.

My understanding is that it depends on temperature. However, at normal physiological temperatures cholesterol increases the overall non-polar bonding in the membrane and thus reduces fluidity.

Source: Life, Science of Biology, 8th Edition, p. 99

Maybe someone else can weigh in here?

 

[ToldYouSo]

My AP Bio teacher talked to us specifically about this topic, that at higher temperatures, cholesterol decreases membrane fluidity but at lower temperatures, cholesterol makes the membrane more fluid then the phospholipids. So basically cholesterol makes the membrane more fluid but only at lower temperatures.

 

[uncbestyet]

Because of the way cholesterol is shaped, part of the steroid ring (the four hydrocarbon rings in between the hydroxyl group and the hydrocarbon "tail") is closely attracted to part of the fatty acid chain on the nearest phospholipid. This helps slightly immobilize the outer surface of the membrane and make it less soluble to very small water-soluble molecules that could otherwise pass through more easily.4

Without cholesterol, cell membranes would be too fluid, not firm enough, and too permeable to some molecules. In other words, it keeps the membrane from turning to mush.

While cholesterol adds firmness and integrity to the plasma membrane and prevents it from becoming overly fluid, it also helps maintain its fluidity.

At the high concentrations it is found in our cell's plasma membranes (close to 50 percent, molecule for molecule) cholesterol helps separate the phospholipids so that the fatty acid chains can't come together and cyrstallize.5

Therefore, cholesterol helps prevent extremes-- whether too fluid, or too firm-- in the consistency of the cell membrane.

 

[ToldYouSo]

Because of the way cholesterol is shaped, part of the steroid ring (the four hydrocarbon rings in between the hydroxyl group and the hydrocarbon "tail") is closely attracted to part of the fatty acid chain on the nearest phospholipid. This helps slightly immobilize the outer surface of the membrane and make it less soluble to very small water-soluble molecules that could otherwise pass through more easily.4

Without cholesterol, cell membranes would be too fluid, not firm enough, and too permeable to some molecules. In other words, it keeps the membrane from turning to mush.

While cholesterol adds firmness and integrity to the plasma membrane and prevents it from becoming overly fluid, it also helps maintain its fluidity.

At the high concentrations it is found in our cell's plasma membranes (close to 50 percent, molecule for molecule) cholesterol helps separate the phospholipids so that the fatty acid chains can't come together and cyrstallize.5

Therefore, cholesterol helps prevent extremes-- whether too fluid, or too firm-- in the consistency of the cell membrane.

Nicely put!

 

[Cholesterol Die]

Thanks a lot for all your replies. You have given me new insight on cholesterol and how important it is to maintain a normal level of the cholesterol. I never thought that it's not good to have very high level of cholesterol and that it is really risky.

 

[plutonium0587]

Because of the way cholesterol is shaped, part of the steroid ring (the four hydrocarbon rings in between the hydroxyl group and the hydrocarbon "tail") is closely attracted to part of the fatty acid chain on the nearest phospholipid. This helps slightly immobilize the outer surface of the membrane and make it less soluble to very small water-soluble molecules that could otherwise pass through more easily.4

Without cholesterol, cell membranes would be too fluid, not firm enough, and too permeable to some molecules. In other words, it keeps the membrane from turning to mush.

While cholesterol adds firmness and integrity to the plasma membrane and prevents it from becoming overly fluid, it also helps maintain its fluidity.

At the high concentrations it is found in our cell's plasma membranes (close to 50 percent, molecule for molecule) cholesterol helps separate the phospholipids so that the fatty acid chains can't come together and cyrstallize.5

Therefore, cholesterol helps prevent extremes-- whether too fluid, or too firm-- in the consistency of the cell membrane.

Just thought I would note that although this is correct, it is from http://www.cholesterol-and-health.com/Cholesterol-Cell-Membrane.html