acetylmandarin

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Oct 20, 2014
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This is probably a very minute detail, but it's bugging me because BR states two different things. On page 34 of their bio II book, it says "Addition of cholesterol to a membrane acts to decrease fluidity. The planar ring inserts between neighboring fatty acid side chains and interferes with the movement of those chains."


And then in passage X, there is a question that asks about the effect of cholesterol on the membrane. The 'correct' answer choice is that "cholesterol has the effect of increasing the fluidity of the membrane by inhibiting hydrocarbon chains from crystallizing."
 

laczlacylaci

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This depends on temperature.

@ low temps, the cell membrane is very non-mobile, addition of cholesterol increases it's fluidity. This is because cholesterol's large size interrupts the hydrophobic interactions of the membrane composed of phospholipids.
@ high temps, the cell membrane is very mobile, addition of cholesterol decreases it's fluidity. The nonpolarity of cholesterol stabilizes the interactions between fatty acid chains and the phospholipid.

A good way to remember this is that: during low temps, molecules are slower in interacting with each other (low KE), so it will want to move less. I like to think about it as it is frozen, doesn't move a lot. Cholesterol will try to reverse that and make it mobile. You can apply the same thinking toward high temp.
 
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acetylmandarin

acetylmandarin

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Oct 20, 2014
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so cholesterol just reverses whatever effect temp has then..thanks!
This depends on temperature.

@ low temps, the cell membrane is very non-mobile, addition of cholesterol increases it's fluidity. This is because cholesterol's large size interrupts the hydrophobic interactions of the membrane composed of phospholipids.
@ high temps, the cell membrane is very mobile, addition of cholesterol decreases it's fluidity. The nonpolarity of cholesterol stabilizes the interactions between fatty acid chains and the phospholipid.

A good way to remember this is that: during low temps, molecules are slower in interacting with each other (low KE), so it will want to move less. I like to think about it as it is frozen, doesn't move a lot. Cholesterol will try to reverse that and make it mobile. You can apply the same thinking toward high temp.[/QUO
 
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Kpw101

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Jul 18, 2013
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This is probably a very minute detail, but it's bugging me because BR states two different things. On page 34 of their bio II book, it says "Addition of cholesterol to a membrane acts to decrease fluidity. The planar ring inserts between neighboring fatty acid side chains and interferes with the movement of those chains."


And then in passage X, there is a question that asks about the effect of cholesterol on the membrane. The 'correct' answer choice is that "cholesterol has the effect of increasing the fluidity of the membrane by inhibiting hydrocarbon chains from crystallizing."
Instead of remembering what it does exactly just remember this one sentence: "Cholesterol optimizes membrane fluidity."

The membrane fluidity gets too high at high temps so Cholesterol optimizes it and makes it less fluid. Membrane fluidity decreases too much at low temps so Cholesterol optimizes it by increasing fluidity. Hope that helps!
 
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