Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 431	Biochemistry	Fall 2001
Lecture Notes:: 3 October	© R. Paselk 2001
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LIPIDS

What is a lipid? The portion of an organism which will partition into a non-polar solvent.

Types of Lipids: (overhead 11.1, P)

• Fatty acids: long chain carboxylic acids. (Figure 9-1 ) [overhead 11.2, P; 12-3, S].Three of the most common are:
  • Palmitic acid: (You can view an on-line model by clicking the Palmitic acid button at this site.)

• Stearic acid:

• Oleic acid: C9-C10 (D⁹double bond (You can view an on-line model by clicking the Oleic acid button at this site.)

• Triacylglycerols: Three fatty acids esterified to glycerol. (Figure p 222) [overhead 11.6]
• Glycerophospholipids: Two fatty acids and a phosphate esterified to glycerol. (Table 9-2, p 223; Figure 9-4, p 223) [overhead 11.8; Table 11.2, P; 11-4 V&V]:

• Sphingolipids: (Figure 9-7, p 226) (overhead 11.16 P; 11-6, V&V)
• Cholesterol: (Figure 9-10, p 228) [overhead 11-9, V&V] (You can view an on-line model by clicking the Cholesterol button at this site.)

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).
• Branched chains (bacterial only): Again, less van der Waals contact and thus lower melting points (more fluid).
• Cholesterol: Its planar shape enables it to stiffen bilayers

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.

Lipid Bilayer: Figures 9-13 - 918, pp 234-6 [overhead 11-12, V&V; 12-11]:

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

Pathway Diagrams

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Last modified 3 October 2001