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Date of Award

5-3-1996

Document Type

Restricted Thesis: Campus only access

Degree Name

Bachelor of Science

Department

Biology

First Advisor

Dr. Suzanne Barbour

Second Advisor

Dr. William Shanabruch

Abstract

Many years ago, the membrane of a cell was thought to be nothing more than a divider which separated the processes of life from the external environment. It was known that the primary constituents of the membrane were molecules known as phospholipids, which are composed of glycerol backbone with a polar head group (i.e. phosphoserine, phosphocholine, phosphoinositol, or phosphoethanolamine) esterified into the sn-3 position and long chain fatty acids (lauric, myristic, palmitic, stearic, arachidic, lignoceric, or arachidonic acid) esterified into the sn-1 and sn-2 positions. There was, however, very little information on how these molecules arranged themselves to form the membrane. In 1925, Gorter and Grendel, using the knowledge that phospholipids would float on the surface of water in a unimolecular layer in which the polar "head groups" face the water and the fatty acyl "tails" point away, demonstrated that the surface area of the phospholipids from an erythrocyte was approximately twice the area of the original cell. They inferred from this that since erythrocytes have no internal membranes, the phospholipids must arrange themselves in some kind of bilayer. Later experiments showed that phospholipids spontaneously form either bilayered sheets or vesicles and that lipid bilayers have a very low density in the center of the bilayer, suggesting that the lipid content in this region significantly exceeds amount of protein. Finally, electron microscopy demonstrated that the membrane looks like a "railroad track," with two dark, parallel outer regions and a clear center area. All this evidence led to Singer and Nicolson to form the model of the membrane we use today, the fluid mosaic model.

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