I had a test today in Biochemstry.

 

In one of the questions the professor asked:

 

Assuming you interfere with the van-der-waals intercations between phospholipids that create a biological plasma membrane, what will happen ?:

 

1) The fluidity of the membrane will go down.

2) The fluidity of the membrane will go up.

3) It will have no effect on the membrane fluidity.

 

Is there a single *definitive* answer for this question ?.

2. Van der Waals forces are responsible for the interactions between the phospholipids' fatty acid chains in the interior of the membrane. Interfering with these interactions will lessen the intermolecular bonding between phospholipids, allowing them to more easily move past each other. This will increase membrane fluidity.

 

This principle can be seen when comparing animal fat and vegetable oil. Animal fat consists primarily of saturated fatty acid chains, while vegetable oils contain unsaturated fatty acid chains. Because the cis double bond in a fatty acid chain creates a "kink" in the chain which disrupts the close packing of the fatty acid chains (thereby decreasing the strenght of the van der Waals interactions), vegetable oils (liquid at room temperature) are much more fluid than animal fats (solid at RT).

Thanks Yggdrasil, that's what I thought so too.

 

I was worried because one of the students said he thought the professor implied during the test, that only cholesterol affects the membrane fluidity, and so changing the van der waals interactions between the phospholipids won't have any meaningful effect. This seems to me like pure B.S. yes, the cholesterol can affect membrane fluidity, but it's not the only factor playing here, and no matter how much cholesterol you have in the membrane, if you interfere with the hydrophobic interactions between the phospholipids, you are going to increase the fluidity.

IIRC bacteria regulate their membrane fluidity through the number of cis bonds in their phospholipids.

Assuming you interfere[/b'] with the van-der-waals interactions

On a side issue, surely this is a poorly phrased question. Interfere with is, to me , equivalent to change. That may mean increase or decrease. On that basis, without knowing which, you cannot give a single, simple answer.

Ophiolite, I thought the exact same but couldn't be bothered sayinhg it

I had a test today in Biochemstry.

 

In one of the questions the professor asked:

 

Assuming you interfere with the van-der-waals intercations between phospholipids that create a biological plasma membrane' date=' what will happen ?:

 

1) The fluidity of the membrane will go down.

2) The fluidity of the membrane will go up.

3) It will have no effect on the membrane fluidity.

 

Is there a single *definitive* answer for this question ?.[/quote']

 

That really is a horrible question.

 

First of all, if the meaning of fluidity in the plasma membrane means that hydrophobic channels allow hydrophobic residues pass, then fluidity will most certainly decrease if you interfere with van der Waals interactions, which increase hydrophobicity and are required in order for amphiphilic proteins to proceed through a channel.

 

If on the other hand, fluidity means breaking up the hydrophobic forces keeping it all together, as in actually making it more "fluid-like" then fluidity will increase.

 

If I were taking that test, I would have assumed the first meaning.

 

I hate multiple choice questions.