*Humboldt State University* ® *Department of Chemistry*

Richard A. Paselk
Chem 431	Biochemistry	Fall 2008
Lecture Notes: 22 October	© R. Paselk 2008
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Lipid Properties: An important consideration for lipids of all sorts is their fluidity. Thus membranes must be fluid enough to allow the diffusion of proteins, transport processes etc. but not so fluid as to weaken the membranes structure. For storage want fat to be fluid enough to flow to fill out body shape at normal operating temperatures. A number of strategies are used by organisms to adjust lipid fluidity:

Fatty acid chain length: longer chains have higher melting points (less fluid at a given temperature). Unsaturation: double bonds introduce a "kink" in the chain, harder to stack, so less van der Waals contact and thus lower melting points (more fluid). (text Figure 10-2cd) Branched chains (bacterial only): Again, less van der Waals contact and thus lower melting points (more fluid).
Cholesterol: Its planar shape (text Figure 10-17) enables it to stiffen bilayers. It is also the source of the steroid nucleus for Steroids (text Figure 10-19)

Lipid Bilayers

Detergents & Micelles: Polar heads of detergents and soaps (such as long chain fatty acids) tend to associate with polar solvents such as water, while non-polar "tails" are excluded by water and are forced to associate with themselves making globules known as micelles. (text Figure 11-4a)

Lipid Bilayer (text Figure 11-4b):

diagramatic drawing of an idealized lipid bilayer

Note that for a flat bilayer the lipids should be cylindrical, while for curved bilayers want "cone" and "wedge" shaped lipds.

The lipid bilayer forms the core for the lipid bilayer membrane as seen in the Fluid Mosaic Model of biological membranes.

Humboldt State University ® Department of Chemistry

Richard A. Paselk

Lipids, cont.

Lipid Bilayers