did they prove that membranes exist as two layers of lipid?
When lipid molecules are in water, the nature of their chemistry
is such that they separate in a way that is a little more
complicated than just a single film of lipid. A key discovery
came in 1925, when two scientists, Groter and Grendel, discovered
that the total surface area of a lipid that could be separated from a red blood cell was
directly related to the
surface area of the red blood cells. Indeed, the amount of
lipid that could be extracted was exactly double that needed to
completely surround the cell.
Maybe the lipid
wrapped around the cell twice! We could guess at this just by knowing the chemistry.
A lipid molecule has two chains of carbon atoms. Think of it like
a kite with two tails. These carbon chains are not attracted to
water, but they are attracted to the carbon chains of other lipids.
The surface area of lipid extracted from a red blood cell is exactly
double the surface area of the cell. This observation led to
the idea that cell membranes must contain two layers
If we know the chemical properties of lipids, we
can figure out how they must self organize in cells, which contain
- One end has chains of carbon, which are
repelled by water
- The other end dissolves in water (that is, is
attracted to water)
- Thus, at the surface of water, one end of the
lipid is attracted to water and the carbon tails point out
away from water.
- A second layer can occur because the carbon
tails of two lipids attract each other.
do you think membrane lipids interact with proteins?