Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 431


Fall 2008

Lecture Notes: 24 October

© R. Paselk 2008


Biological Membranes

Membrane shows up as a bilayer structure in electron micrographs (text Figure 11-1).

Fluid Mosaic Model: (text Figure 11-3)

This model has as its core element a lipid bilayer (predominantly glycero-phospholipid). This bilayer makes a very effective barrier for the flow of charged and polar species between aqueous compartments. Within the bilayer itself, however, flow occurs readily - it is a two- dimensional liquid with a viscosity similar to olive oil. Thus we see rapid exchange between adjacent phospholipid molecules on a face of the bilayer, but very rare exchange between faces (the polar "head" groups would have to cross the non-polar bilayer interior). A lipid bilayer membrane thus separates the interior of the cell from the outside.

Of course a cell also needs to communicate with the outside world - doors and windows are needed. Such communication occurs largely through proteins acting as pores, gates, and shuttles.

Pathway Diagrams

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Last modified 25 October 2008