does alcohol affect the structure of a cell membrane?
the normal organization of the
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.
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.)
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
that are not in their normal shape in the cell membrane may
not be able to do their jobs.
unit on "Making Protein Machinery"