Toxic Substance

How does alcohol affect the structure of a cell membrane?

Alcohol disrupts the normal organization of the lipid carbon chains (see picture below.)

Your scientist/author of this module believes that alcohol sticks to a membrane near its surface with water. Some of the evidence that supports this idea was obtained with a simple artificial lipid membrane. Several methods demonstrate that alcohol binds just underneath the charged head group of surface lipid, displacing some of the water that is normally there. The importance of this physical disruption is not so much what it does to the lipid, but what it does to the proteins (not shown) that are embedded in the lipid. Disturbing the shape of the lipids changes the shape of the proteins, and thus changes the functions of the protein.

This drawing uses lollipop symbols for the phospholipids (the lipid portion of cell membranes.) The presence of alcohol (the black blob) shifts the lipid molecules out of place and breaks up their orderly arrangement. This makes the membrane more liquid like. (Like changing cold butter to a more liquid form like warm margarine.)

Why does shifting the lipids cause problems?

Think about how the substitution of alcohol for water might affect the large, complex sugars and proteins that are embedded in the lipid membrane. Ask yourself:

Wouldn't the substitution cause proteins to change shape?
If they changed shape, could that cause them to change function?

Although the lipid of a membrane has no special function of its own, it does influence the large functional molecules (proteins and sugars) that the membrane contains. This is not a good thing.

Changing a protein's shape or location can change the protein's function. Some membrane proteins are affected more by alcohol than are other proteins.

For a learning activity about alcohol intoxication, see Activity #4

Proteins that are not in their normal shape in the cell membrane may not be able to do their jobs.

See unit on "Making Protein Machinery"