lipids and membranes - · lipids and membranes. ... membrane lipids include phospholipids,...
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Fatty acids
Nomenclature: C1 (COOH), C2, C3, etc. αC = C2, ßC = C3, etc.18 C’s with 2 double bonds: C18:2(Δ9,12)(“Δ9” 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 (Δ9)• Linoleic acid—C18:2 (Δ9,12)
Fatty acids
• Palmitic acid—16:0• Stearic acid—18:0• Oleic acid—18:1 (Δ9)• Linoleic acid—18:2 (Δ9,12)
Long, straight chains are less soluble (in aqueous medium)Short chains, and double bonds reduce melting temperature and increase solubility
http://www.uptodate.com/contents/fish-oil-and-marine-omega-3-fatty-acids
Long chain n-3polyunsaturatedfatty acids (PUFA),found in fish oil butprobably synthesizedby algae in fish diets,have important effects on humanhealth.
Long chain saturated fattyacids are pheromones formany insects, advertisingfecundity in queens and/orsuppressing reproduction inworkers.
Van oystaeyen et al., Science 343, 287 (17 Jan 2014)
Membrane lipids (phospholipids)
glycerol C1-attached fatty acid normally saturated glycerol C2-attached fatty acid normally unsaturated glycerol C3: phosphate plus hydrophilic group...
P-lipid breakdown by hydrolysis: catalyzed by phospholipases e.g.: snake venom P-lipase (PLA2) hydrolyzes C2 fatty acid, which bursts erythrocytes
Membranes Lipid bilayer: heads in contact with aqueous solution; tails isolated from it. Note the different lipids in membranes: inner and outer leaflets are distinct.
erythrocyte: • inner: phosphatidylethanolamine,
phosphatidylserine predominate • outer: phosphatidyl choline, sphingomyelin
predominate
Lipid solubility
! on water surface: heads in water, tails in air ! submerged single tail lipids (e.g., sodium
laurylsulfate) at “critical micelle concentration”: spontaneous formation of micelles
! submerged phospholipids form liposomes, bilayer leaflets
• longer chains raise the transition temperature, decrease fluidity
• double bonds lower the transition temperature, increase fluidity
• membranes leak during the transition • cholesterol (et al.) makes the gel more fluid and
the liquid crystal less fluid (also Ca2+) • enzymes in membranes generally work better in
liquid crystal phase, but complexes may stay together better in a gel
Lipid compositionUnsaturatedPalmitic 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%PolyunsaturatedLinoleic acid: 3.5–21.0 %α-Linolenic acid: <1.5%
ProblemsFree fatty acidsPeroxidesUV absorption (conjugated double bonds)1,2 and 1,3 diacylglycerols
Olive oil “Tests indicate that imported “extra virgin”olive oil often fails internationaland 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 triglyceridesMembrane lipids include phospholipids, sphingolipids, and sterolsTemperature-induced phase transitions represent a change from
close-packed to more open conformations