Cholesterol and Plasma Membrane Fluidity

[MedPR]

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In eukaryotic cells, the plasma membrane contains relatively large amounts of cholesterol. At such high concentrations, cholesterol has the effect of:

A. decreasing the fluidity of the membrane by inhibiting hydrocarbon chains from crystallizing
B. decreasing the fluidity of the membrane by promoting hydrocarbon chain crystallization
C. increasing the fluidity of the membrane by inhibiting hydrocarbon chains from crystallizing
D. increasing the fluidity of the membrane by promoting hydrocarbon chain crystallization.

 

[Pisiform]

C ??

 

[MedPR]

C ??

Yes. I thought Cholesterol made the plasma membrane more rigid?

 

[Ssina]

I thought cholesterol varies with temperature... like if it's too cold, it'll make the membrane more fluid, and when too hot, it'll make it less fluid!

 

[chiddler]

I thought cholesterol varies with temperature... like if it's too cold, it'll make the membrane more fluid, and when too hot, it'll make it less fluid!

I agree!

"2. cholesterol effects on membrane fluidity:

At high temperatures cholesterol tends to reduce membrane fluidity, probably by interacting with the hydrocarbon tails of the phospholipid and glycolipid molecules. At low temperatures cholesterol helps prevent membranes from freezing and thus tends to maintain membrane fluidity."

googled, no idea if accurate but rings cell bio bells.

This doesn't really explain why though. Does anybody know how cholesterol functions in increasing rigidity? More fluidity is understandable because it's kinky (aww yeah!) and is similar to unsaturated phospholipids. But the opposite?

 

[MedPR]

I figured it would decrease membrane fluidity by interrupting the continuity of neighboring phospholipids.

 

[chiddler]

I figured it would decrease membrane fluidity by interrupting the continuity of neighboring phospholipids.

Close association allows more intermolecular forces = more rigid. Interrupting the continuity = less intermolecular forces and therefore more fluidity, right?

 

[Pisiform]

You are right about temperature thingy. However, cholesterol just prevent extremes and maintains homeostasis in the cell membrane - not too fluid and not too rigid. The only plausible answer was C because if you imagine if you add impurities to something (here cholesterol I though of as) then the particles won't come together just like in crystallization in chemistry. you need less impurity to make a good pure crystal ... presence of cholestrol would disrupt that and hence increasing fluidity. But I agree the question is a bit weird

 

[MedPR]

Close association allows more intermolecular forces = more rigid. Interrupting the continuity = less intermolecular forces and therefore more fluidity, right?

You are right about temperature thingy. However, cholesterol just prevent extremes and maintains homeostasis in the cell membrane - not too fluid and not too rigid. The only plausible answer was C because if you imagine if you add impurities to something (here cholesterol I though of as) then the particles won't come together just like in crystallization in chemistry. you need less impurity to make a good pure crystal ... presence of cholestrol would disrupt that and hence increasing fluidity. But I agree the question is a bit weird

Makes sense. I had that entirely backwards in my mind. I picked answer B, btw.

Thank you.

 

[SaintJude]

Yeah, I doubt a specific question on the effects of cholesterol on membrane fluidity will appear on the MCAT, because it's effect has been noted to both increase and decrease fluidity. A 2004 research publication was posted in the Cellular Biochemistry Journal that concluded that cholesterol decreases membrane fluidity.

It says " Increasing membrane C/PL causes a decrease in membrane fluidity, and these changes are associated with a reduction in membrane permeability, a distortion of cell contour and filterability and a shortening of the survival of redcells in vivo."

But for a simplified concept for intro Bio, Pisiform is right on point. Cholesterol would disrupt the constant pattern and reduce hydrocarbon chain crystallization

 

[MedPR]

Yeah, I doubt a specific question on the effects of cholesterol on membrane fluidity will appear on the MCAT, because it's effect has been noted to both increase and decrease fluidity. A 2004 research publication was posted in the Cellular Biochemistry Journal that concluded that cholesterol decreases membrane fluidity.

It says " Increasing membrane C/PL causes a decrease in membrane fluidity, and these changes are associated with a reduction in membrane permeability, a distortion of cell contour and filterability and a shortening of the survival of redcells in vivo."

But for a simplified concept for intro Bio, Pisiform is right on point. Cholesterol would disrupt the constant pattern and reduce hydrocarbon chain crystallization

Thanks