LIPIDS AND MEMBRANES

Fatty acids Hydrocarbon chain (saturated or un-) Carboxylic acid group C C HH HH

Fatty acids Nomenclature: C1 (COOH), C2, C3, etc.  C = C2, ßC = C3, etc. 18 C’s with 2 double bonds: C18:2(  9,12) (“  9” means between C9 and C10) (double bonds are normally at 9, 12, 15 and are cis) Palmitic acid—C16:0 Stearic acid—C18:0 Oleic acid—C18:1 (  9) Linoleic acid—C18:2 (  9,12)

Fatty acids Palmitic acid—16:0 Stearic acid—18:0 Oleic acid—18:1 (  9) Linoleic acid—18:2  9,12) Long, straight chains are less soluble (in aqueous medium) Short chains, and double bonds reduce melting temperature and increase solubility

Fats and oils --storage forms of C and energy-- accumulate in lipid bodies An adipocyte

Archeal membrane lipids have structures analogous to phospholipids

Phase transitions

Resistance to cold is associated with higher concentrations of linolenic acid.

Lipid composition Unsaturated Palmitic acid: 7.5–20.0% Stearic acid: 0.5–5.0% Mono-unsaturated Oleic acid: 55.0–83.0% Palmitoleic acid: 0.3–3.5% Polyunsaturated Linoleic acid: 3.5–21.0 % α-Linolenic acid: <1.5% Problems Free fatty acids Peroxides UV absorption (conjugated double bonds) 1,2 and 1,3 diacylglycerols Olive oil “Tests indicate that imported “extra virgin”olive oil often fails international and USDA standards - UC Davis Olive Center, July 2010”

Summary Fatty acids are distinguished by length and presence of double bonds: palmitic, steric, oleic, and linoleic acids are common. Storage lipids are generally triglycerides Membrane lipids include phospholipids, sphingolipids, and sterols Temperature-induced phase transitions represent a change from close-packed to more open conformations