Lipids

Chapter 10 - Lipids

• 10.1 Storage Lipids

• 10.2 Structural Lipids in Membranes

• 10.3 Lipids as Signals, Cofactors and Pigments

• 10.4 Working with Lipids

10.1 Storage Lipids

• Fatty Acids - Structure

• Fatty Acids - Physical Properties

• Triacylglycerols - the simplest Lipids

• Triacylglytcerols in Energy Storage Thermal insulation

• Triacylglycerols in food

• Waxes

Fatty Acid Structure

• Carboxylic Acids (COOH is C1)• hydrocarbon tails (C4 - C36)• Saturated fatty acids N:0• Unaturated Fatty acids

• Double bonds specified by (Δn)

• Branches

Fatty Acids - Physical Properties

• Solubility• Longer chains

• more hydrophobic, less soluble

• Double bonds increase solubility• Melting points

• Depend on chain length and saturation• Double bonds lead acyl chain disorder and

low melting temps• Unsaturated FAs are solids at Room Temp

Triacylglycerols

• Glycerol head group HO-CH2-CH(OH)-CH2-OH

• Ester linkage from each hydroxyl to Fatty acid

• Carboxylate charge is lost • TAGs more

hydrophobic than FAs

Triacylglycerols in Energy Storage & Thermal insulation

• Concentrated source of energy– Energy derived from oxidation reactions– More completely reduced state yields 2x the

energy/g as Carbohydrates

• Pure non-aqueous phase– Lipases hydrolize the ester linkages to

release Fatty Acids

Triacylglycerols in food

• Vegetable Oils – unsaturated- catalytic hydrogenation reduces

double bonds

- less specific than enzymatic methods makes some trans-fats

Waxes

• Esters of long chain fatty Acids with long chain alcohols

• Higher melting points• Hydrophobic

10.1 Summary

• Lipids are water insoluble

• Common Fatty Acids have 12-24 carbon atoms (an even number)

• Triacyl glycerols primary storage fats in food.

10.2 Structural Lipids in Membranes

Glycerophospholipids

• Phosphorylation of Glycerol creates a stereocenter on C2– L glycerol 3 phosphate

head group adds a negative charge

– Phospho diesters with:• Ethanolamine, Choline,

Serine, Glycerol, Inositol Phosphate, Phosphatidyl Glycerol

2 Fatty Acid chains esterified to remaining hydroxyls (diacyl

glycerol)• Common Glycerophospholipids have

– 16:0 or 18:0 at C1– 18:1 Δ(2) or 20:1 Δ(2) at C2

Ether Lipids

• Ether linkage instead of ester at C1

• Plasmalogens have a C1=C2 double bond

• Platelet activating factor is a signalling lipid with:– saturated acyl chain at

CI (ether linkage)– acetyl ester at C2– phospho-choline on C3

Galactolipids and Sulfolipids in Chloroplasts

• Galactose (or DiGal) attached to Glycerol C3

• Sulpho lipids contain sulphonate on sugar

• Sulphonate charge replaces typical phosphate charge

Archael "Extremophile" Lipids• Longer acyl chains and dual head groups can

can replace 2 normal phospholipids – Replace a bilayer with a monolayer

• Ether linkages• More stable at high temperatures, Acid

Environments

Sphingolipids• Sphingosine is a combination

acyl chain & Head group(HO-1CH-CH=CH-(CH2)12-CH3 2CH-NH3

3CH2-OH

• Acyl chain in amide linkage at C2 makes a ceramide

Head groups at C3• Sphingomyelins

– Phosphocholine or Phosphoethanolamine

• Glycosphingolipids– Cerebrosides have

Glucose, galactose– Globosides have

simple neutral Oligosaccharides,

– Gangliosides have more complicated anionic oligosaccharides

Glyco-sphingolipids specify cell

identitity

• Blood Groups–O, –A (+GalNac), –B (+Gal)

Lipid Degradation in Lysosomes

• Phospholipase A1 cleaves ester linkage at C1– glycerophospholipid =>

lysophospholipid + FA1

• Phospholipase A2 is a lysophospholipase– cleaves ester linkage at C2– lysophospholipid =>

Glycerophosphate head group + FA2

• Phospholipase C cleaves phospho-glycerol ester linkages– glycerophospholipid => diacyl

glyceral + phospho head group

Sterols

• Have 4 fused rings

• Cholesterol is the major sterol in vertebrates

• Steroid Hormones– Testosterone,

Estrogen

10.2 Summary

• Polar Lipids major constituent of membranes• Glycerophospholipids are charged depending

on constituents• Galactolipids are abundant in chloroplasts• Archaebacteria have extreme lipids• Sphingolipids are built on a sphingosine

framework• Sterols have a polycyclic aromatic ring

structure

10.3 Lipids as Signals, Cofactors and Pigments

• Phosphatidylinositol signalling• Sphinogosine• Eicosanoids• Steroid Hormones• Plant signalling• Vitamin A and D• Vitamin E and K - Redox Cofactors• Dolichols

Phosphatidylinositol signaling

• PI is phosphorylated to give PI 4,5 bisphosphate

• On the inner (cytoplasmic) leaflet of the cell membrane

• Phospholipase C cleaves PI 4,5 bisphosphate to give– IP3 and DAG– both molecules active in signalling through

protein kinase C• Pleckstrin homology domains bind to inositol

3,4,5 triP

Homo sapiens (human) http://www.genome.jp/kegg/pathway/hsa/hsa04070.htm

Eicosanoids• Are derived from Arachadonic Acid 20:4(Δ5,8,11,14)• NSAIDs (Aspirin and ibuprofin) block production of

Prostaglandiins and thromboxanes• Prostaglandins - C8-C12 bond generates 5 membered ring. Stimulate

adenylyl cyclase

• Thromboxanes - C8 -C12 bond + Oxygen in heterocyclic ring

• Leukotrienes involved in asthma and other processes

Steroid Hormones

• low solubility in water • transported by

proteins, • can pass through

membranes

Vitamin A and D• Isoprene is a common

precursor for sterols, Vitamin D and Vitamin A– CH2=C(CH3)-CH=CH2

• D vitamins derived from Sterols

Vitamin E and K - Redox Cofactors

• Vitamin E and other tocopherols are antioxidants• Vitamin K is an isoprenoid blood Clotting cofactor

– Warfarin is a vitamin K derivative (named after the Wisconsin Alumni Research Foundation WARF)

– rat poison that kills by inducing hemorrhage, internal bleeding

– Can be used medically to inhibit clotting

• Dolichols– Serve as membrane anchors for the assembly of

oligosaccharides by glycosyl transferases

10.3 Summary

• Minor lipids are essential cofactors

• PI bisP => inositol trisP + DAG

• Eicosanoid hormones from arachidonic acid

• Steroid Hormones

• Fat Soluble Vitamins

• Fat soluble quinones - electron transport

• Dolichols - membrane anchors for "solid phase" oligosaccharide synthesis

10.4 Working with Lipids

• Lipid Extraction

• Adsorption Chromatography

• Gas Liquid Chromatography

• Specific Hydrolysis

• Mass Spectrometry

Lipid Extraction

• Lipid Definition: Any of a group of organic compounds, including the fats, oils, waxes, sterols, and triglycerides, that are insoluble in water but soluble in nonpolar organic solvents, are oily to the touch, and together with carbohydrates and proteins constitute the principal structural material of living cells. - First step is an organic solvent extraction to separate the lipids (by definition) from everything else - Commonly Chloroform Methanol Water Mixtures

Adsorption Chromatography

• Silica gel is insoluble in and more polar than CHCl3

• Polar lipids adsorb from the solvent, bind to the column

• Elution with successively more polar solvents eg. Acetone then MeOH

Gas Liquid Chromatography

• Good for analysis of volatile components

• Fatty acids analysed as Methyl esters after acid or base hydrolysis in MeOH

• Adsorption from gas phase to the liquid (instead of solid from liquid) slows the passage through the column

Specific Hydrolysis

• Acid or base hydrolysis is non-specific

• Enzymatic hydrolysis requires specific interactions

• Lipid identity can be deduced from Chromatograms taken before and after hydrolysis

Mass Spectrometry• Chromatography fractions or continuous flow can be

monitored by MS• Accurate masses of intact lipids, specific hydrolysis products,

and internal fragments can be used to deduce structure

10.4 Summary

• Extraction and Chromatography

• Phospholipase hydrolysis

• ID by chromatagraphy, specific hydrolysis and/or Mass. Spec.