Ethanol and cell membranes

[Mdr1985]

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I've asked this question to 10 different people, professors included, and managed to get 10 different answer. . .

Ethanol is polar, correct? (my biology instructor today told me it wasn't, whilst my ochem professor told me it was)

The phospholipid bilayer depends on being surrounded by a polar substance to hold it together, and if surrounded by non polar substances would dissociate. . . correct?

If the above two are in fact true, why is it that ethanol dissolves cell membranes? If it's polar, I'd think it would act like water does and hold the membrane together, but everyone says ethanol dissolves cell membranes. What am I missing? I'd understand it it was cycloheptanol or something that was mostly organic/non-polar, but we're talking about ethanol here. . . two little C's and a very polar OH group.

Any insight would be greatly appreciated!

 

[notbobtrustme]

Ethanol is only slightly polar. It doesn't have enough charge separation to form a distinct polar/non-polar layer like water does. It is polar enough to dissolve in water though.

It's just a question of semantics.

 

[aspiringdoc09]

I've asked this question to 10 different people, professors included, and managed to get 10 different answer. . .

Ethanol is polar, correct? (my biology instructor today told me it wasn't, whilst my ochem professor told me it was)

The phospholipid bilayer depends on being surrounded by a polar substance to hold it together, and if surrounded by non polar substances would dissociate. . . correct?

If the above two are in fact true, why is it that ethanol dissolves cell membranes? If it's polar, I'd think it would act like water does and hold the membrane together, but everyone says ethanol dissolves cell membranes. What am I missing? I'd understand it it was cycloheptanol or something that was mostly organic/non-polar, but we're talking about ethanol here. . . two little C's and a very polar OH group.

Any insight would be greatly appreciated!

It shares both polar and nonpolar characteristics. It's a solvent. It's polar due to the -OH group and nonpolar due to the hydrocarbon chain. If you had organic chem., then when you compare ethanol to ethane, clearly ethanol wins the polarity contest. It can be miscible with nonpolar substances. Or it can mix with water due to hydrogen bonding. As you know, the phospholipid bilayer is also amphipatic, so the polar heads face the polar solvents (i.e. water) and the nonpolar tails are hydrophobic. Think in terms of the fluid mosaic model. The cell membrane contains lipids (such as cholesterol) and proteins. Ethanol due its polar and nonpolar properties can leak through the cell membrane and destroy the fluidity by denaturing proteins and affecting the lipids (Like dissolves like in this case). Therefore, the cell membrane will have holes due to this disruption. Also, think about ethanol effects on DNA. We use ethanol to extract DNA due to its ability to break the DNA's bonding with water. It's all about destroying bonds and how structures function in the default state. Denatured alcohol is used in histoprep to preserve cells and cellular structures, but that's a whole different beast. Hopefully, this helps from a biochemistry perspective.