Levels of Organization Image Map

 


How do we know what chemicals make up a membrane?

The first clue was the observation that fatty substances easily entered cells, while other kinds of chemicals passed slowly or not at all. Secondly, if you pull out the red pigment in red blood cells, most of what is left is lipid.

Oil Shaken in Water Picture

Oil Layered on Water Picture

You can observe how lipids organize themselves. Have you ever seen cold soup with a film of fat on top? Or do this: shake up a bottle of water that has some oil in it. If you let the water stand undisturbed for a few hours, you will see the oil rise to the top and form a film all by itself. Vessels Image

 

Using vessels like those shown on the right, we can collect oil separate from water by draining off the lower liquid compartment. Membrane lipids can be extracted by homogenizing tissue in water and letting the lipid separate. More efficient is to use an organic solvent, like hexane (see toxic hazards in protein unit). Such solvents can produce purer separations of oil from water.

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