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PROFESSOR; Now, another important lipid that doesn't look anything like
what I've been talking, but is extremely important, is our friend
cholesterol. Cholesterol gets a bad name, but you couldn't
live without it because what this guy does-- now why is this a surfactant?
Well, obviously this is all hydrocarbon here. And the only polar group was this OH.
So it turns out, this is so insoluble in water that, by itself, it's not a
very good surfactant. But what it does do is dissolve very well
in a lipid bilayer. And in fact, this guy intercalates into the
phospholipid membranes. It increases the packing density, interestingly
enough, and it basically decreases the fluidity of the membrane.
So if you want to make that membrane stiffer, you put cholesterol in it.
And if you didn't have cholesterol, you would just be a pile of jelly.
It's the thing that creates a structural material out of that membrane.