Cell Membrane Hydrophilic
Country: United States
Date: Fall 2010
What in the cell membrane attracts water?
It's what 'on', not 'in' the cell membrane, that attracts water. If
you look at a cut-away of the cell membrane, it looks like a sandwich
in a way. Think of one side of the sandwich as the 'inside' -- facing
the cytoplasm of the cell -- and the other side as the 'outside',
facing the extracellular matrix. The 'bread' of this sandwich -- the
layers facing the cytoplasm or facing outside the cell -- is made of
ions that attract water, and allow the cell to contact water. The
inside of the cell is also water, so the membrane must have ions on
the inside surface too. But between the inside surface and the outside
surface (the 'meat' of the sandwich) is made of stuff that is not
attracted to water, but those are shielded from the water by the ions,
just like the break shields the greasy meat from your hands.
The actual molecules of cell membranes are 'lipids', but with an ionic
head group. Think of them as a pushpin, with a head and a long 'tail'
The long tails attract each other to form a flat sheet (called a
lamella), with the ionic head groups facing outward. You can search
for images of this on the internet or in biology books that depict it
To answer your explicit question, basically, the ions on the one end
of the lipid molecules are able to interact with water molecules very
readily, and that is what attracts the water. A more detailed
explanation would require some thermodynamics -- but not sure of your
grade level, so let me know if you want more detail.
I don't know your grade level, so I'm speaking in general terms - let
me know if you want a more technical description. There are several
other posts on AAS that address other aspects of cell membrane
function and content:
Hope this helps,
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Update: June 2012