Levels of Organization Image Map
What do scientists know about lipid organization in membranes?

Scientists believe that lipids form a double layer, because the alternative is for the charged groups to face each other. Because the electrical charges would repel each other, and because the charge groups are attracted to water, this is the logical way for lipids to self-organize (see below).
Lipid Organization Image
Membranes self-organize

Ever notice that when your mother cooks soup, when it cools the fat rises to the top and congeals? When hot, the fats do not aggregate well, but rather mix in with the water part of the soup. What happens if you pour a little oil or other kind of fat into a bowl of water? It will self-organize as a film of oil at the top. It floats because fat is lighter than water. It forms a film because the electrical forces of water grab the charged head groups and make them line up.
  • The amount of lipid in red blood cells, which have only protein on the inside,  is double what it would take to cover the outside diameter of the cell. Thus, it must occur in two layers. (See " How We Find Out" for more details.)
  • In water, lipids group together spontaneously to form membranes. Think about what this says about the importance of water. 
So how are proteins and lipids related to each other in the membrane? 
  • Scientists know that proteins are closely associated with membranes, because dissolving membranes will pull out both protein and lipid.
  • Drs. Danielli and Davson (see "Story Time") thought that membranes were built like a sandwich, with the protein "bread" on the outside and a  double layer of lipid "meat" on the inside.

  This is how Danielli and Davson thought about the structure of membranes. The blobs at the top and bottom of the diagram represented assumed layers of protein.

Membrane Image
Remember how the proteins are positioned in the cell membrane? If not, click here to go back.

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