AGRC1020 Lecture Notes - Lecture 1: Lipid Bilayer, Membrane Fluidity, James Danielli
6 Aug 2018
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Document Summary
The plasma membrane separates the living cell from its nonliving surroundings. This thin barrier, 8 nm thick, controls traffic into and out of the cell. Like all biological membranes, the plasma membrane is selectively permeable, allowing some substances to cross more easily than others. The main macromolecules in membranes are lipids and proteins, but carbohydrates are also important. Phospholipids and most other membrane constituents are amphipathic molecules. Amphipathic molecules have both hydrophobic regions and hydrophilic regions. The arrangement of phospholipids and proteins in biological membranes is described by the fluid mosaic model. Membrane models have evolved to fit new data. Models of membranes were developed long before membranes were first seen with electron microscopes in the. In 1915, membranes isolated from red blood cells were chemically analyzed and found to be composed of lipids and proteins. In 1925, e. gorter and f. grendel reasoned that cell membranes must be a phospholipid bilayer two molecules thick.
