(A) Which two out of the following possible properties of cholesterol in membran
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Question
(A) Which two out of the following possible properties of cholesterol in membranes are INCORRECT?
Select the two that are False.
1. Its presence in the membrane impedes the close packing of phospholipid tails at low temperature, helping to maintain membrane fluidity.
2. Its large polar head group makes it highly energetically unfavorable for it to flip between the leaflets of the membrane, and a given cholesterol molecule does so spontaneously only about once per day.
3. At high concentrations it keeps the membrane fluid over a large temperature range, eliminating a sharp phase transition.
4. Its presence in the membrane impedes the flexion of phospholipid tails at high temperature, limiting excessive membrane fluidity.
5. It is found in essentially all membranes in all cells, including procaryotic, plant and animal cells.
6. It can flip between leaflets of the bilayer quickly, contributing to the ability of membranes to rapidly change their curvature.
B) Which two out of the following possible properties of phospholipids in membranes are INCORRECT?
Select the two that are False.
1. Their head groups include derivatives of amine alcohols, sugars and amino acids.
2. They are not the only type of long-chain lipids in eucaryotic cell membranes.
3. They can rotate, diffuse laterally, and flex their fatty acid chains very rapidly in membranes at the temperature of the living cell.
4. They can flip between leaflets of the bilayer quickly, contributing to the ability of membranes to rapidly change their curvature.
5. Their different major varieties are uniformly distributed between leaflets of the smooth endoplasmic reticulum after synthesis, but are highly asymmetrically distributed between leaflets of the plasma membrane.
6. The complex phospholipid composition of cell membranes gives those membranes a much sharper phase transition temperature than that of artificial membranes composed of a pure single variety of phospholipid
Explanation / Answer
2) Its large polar head group makes it highly energetically unfavorable for it to flip between the leaflets of the membrane, and a given cholesterol molecule does so spontaneously only about once per day.
5) It is found in essentially all membranes in all cells, including prokaryotic, plant and animal cells.
These two statements are false.
B)
4. They can flip between leaflets of the bilayer quickly, contributing to the ability of membranes to rapidly change their curvature.
6. The complex phospholipid composition of cell membranes gives those membranes a much sharper phase transition temperature than that of artificial membranes composed of a pure single variety of phospholipid.
These two statements are incorrect.
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