Re: How are cell membranes affected by alcohol and chloroform?

To understand the effects of chemicals like alcohol and chloroform on membranes, you first have to understand the structure of water and the cell membrane.  Water molecules interact strongly with one another through "hydrogen bonds".  The ability to form hydrogen bonds arises from the presence of polarized chemical bonds within a molecule.  Each of the O-H bonds of water is highly polarized.  (CLICK HERE FOR AN INTERESTING IMAGE OF SUCH INTERACTIONS)

In contrast to water, oganic solvents like ethanol and even more so chloroform, are non-polar because they can make few if any hydrogen bonds.

The structure of water leads to the hydrophobic effect.  Molecules, or parts of molecules, that are unable to form hydrogen bonds have a hard time dissolving in water.  The larger the molecule and the fewer hydrogen bonds it can make, the less water soluble it will be.

Biological membranes are composed of lipids and proteins.  The lipid molecules are amphiphilic -- that means they have a domain that is very soluble in water, because it can make  hydrogen bonds, and a domain that is hydrophobic -- which cannot.  The hydrophobic domains are packed together in the interior of the lipid bilayer.  This structure is stable in a hydrophilic enviroment (like water).  But if the environment becomes hydrophobic, because of the presence of hydrophobic molecules (like ethanol or chloroform), the bilayer structure will be destabilized -- it will break down.  As the membrane breaks down, holes form within it, allowing cellular contents to escape.  As the membrane breaks down, the cell will die.