What is Lipid Lipids: insoluble in water, but soluble in organic solvents including diethyl ether, chloroform, methylene chloride, and acetone Amphipathic: hydrophobic in nature Lipids include: Open Chain forms fatty acids, triacylglycerols, sphingolipids, phosphoacylglycerols, glycolipids, lipid-soluble vitamins prostaglandins, leukotrienes, and thromboxanes Cyclic forms cholesterol, steroid hormones, and bile acids

Lipid: Structure Open chain: Cyclic forms/Fused ring: long nonpolar tail with a polar head Saponifiable Cyclic forms/Fused ring: - based on the steroid ring skeleton

LIPID: CLASSESS Fatty acids and their derivatives Triacylglycerols Phosphoacylglycerol, phosphoglycerides Sphingolipids Wax esters Isoprenoids (based on isoprene structure)

LIPID: Structural features / phosphoacylglycerol GENERAL STRUCTURE The structural features of storage and membrane lipids. (a) The storage lipids are composed of nonpolar triacylglycerol. (b) The membrane lipids are composed of glycerophospholipids and sphingolipids which have polar and nonpolar regions

Fatty Acids Nonpolar hydrophobic tail Polar hydrophilic head Fatty acid: a molecule with a carboxyl group as the polar end and a hydrocarbon chain as the hydrophobic/nonpolar end. an unbranched-chain carboxylic acid, mostly in even numbers of carbon Nonpolar hydrophobic tail Polar hydrophilic head

Fatty Acids Nonpolar hydrophobic tail Polar hydrophilic head derived from hydrolysis of animal fats, vegetable oils, or phosphodiacylglycerols of biological membranes Amphiphatic Nonpolar hydrophobic tail Polar hydrophilic head

Fatty Acids Length of fatty acid plays a role in its chemical character • Usually contain even numbers of carbons (can contain odd, depending on how they are biosynthesized) • FA - C=C bonds, are unsaturated fatty acid - C-C bonds, are saturated fatty acid

Fatty Acids

Fatty Acids Unsaturated fatty acids have lower melting points than their saturated counterparts; the greater the degree of unsaturation, the lower the melting point

Fatty Acids In most unsaturated fatty acids, the cis isomer predominates; the trans isomer is rare 16:19 Palmitoleic acid Cis double bond results in a bent chain and lower mp.

Fatty Acids Palmitoleic 16:19 – degree of unsaturation or abbreviation symbol CH3(CH2)5CH=CH (CH2)7COOH – chemical formula 7 9 5 3 1 11 13 15 Palmitoleic acid

Fatty Acids Oleic acid 18:19 Stearic acid 18:0 structure

Fatty Acids

CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH CH3(CH2)3(CH2CH=CH)4(CH2)3 COOH Fatty Acids - examples Stearic 18:0 CH3(CH2)16COOH Oleic acid 18:19 / 18:19 / 18:1- 9 CH3(CH2)4CH2CH2CH2CH=CH(CH2)7COOH Palmitoleic 16:19 CH3(CH2)5CH=CH (CH2)7COOH Linolenic 18:29,12 CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH Arachidonic 20:45,8,11,14 CH3(CH2)3(CH2CH=CH)4(CH2)3 COOH

Triacylglycerols Glycerol part Fatty acid chains Triacylglycerol (triglyceride): an ester of glycerol with three fatty acids Nonpolar class of lipid, very hydrophobic Glycerol part Fatty acid chains

Triacylglycerols (TAGs) TAGs which are solids at room temperature are rich in saturated acids and are called fats. TAGs which are liquids at room temperature are rich in unsaturated acids and are called oils. e.g. oil seeds include peanut, corn, safflower, palm, olive and soybean.

Triacylglycerols (TAGs) Hydrolysis of TAGs will produce 1 glycerol and 3 fatty acids. Biologically this is done by lipases. Chemically base hydrolysis is called saponification.

Hydrolysis of Triacylglycerols (TAGs)

Saponification Saponification – reactions of triacylglycerol with … to produce … , which is the sodium salt

Phosphoacylglycerols (Phospholipids) Phosphatidic acid When one alcohol group of glycerol is esterified by a phosphoric acid rather than by a carboxylic acid, phosphatidic acid produced Phosphatidyl ester = phosphoacylglycerol 1 glycerol bonded to 2 fatty acids + phosphate group

Phosphoacylglycerols = glycerophospholipids Phosphoacylglycerols – amphiphatic, polar, hydrophilic The second most abundant group of naturally occurring lipids, and they are found in plant and animal membranes second alcohol

Phosphatidyl esters = phosphoacylglycerol = glycerophospholipids Fatty acid

Functions of phospholipids: as participate in the transduction of biological signals across the membrane play an important role in the important source of acetylcholine (common neurotransmitter substance occur in mammals)

Phospholipids glycerophospholipids & sphingolipids have a polar head & 2 hydrophobic tails Extra space taken by the non-polar tails, these lipids unable to assemble into micelles So, bilayer is form - nonpolar side combines by hydrophobic interactions to exclude water in the centre region of bilayer Salts of fatty acid with polar head and a single nonpolar assemble into spherical structures - micelles

Sphingolipids No glycerol Contain sphingosine, a long-chain amino alcohol Found in Abundant in nervous system Bares structural similarity to phospholipids

Sphingolipids (simplest) Primary alcohol group esterified to phosphoric acid which esterified to choline

Sphingolipids + sugar residue = Glycolipids glycosphingolipid Glycolipid: a compound in which a carbohydrate is bound to an -OH of the lipid In most cases, sugar is either glucose or galactose many glycolipids are derived from ceramides Glycolipids with complex carbohydrate moiety that contains more than 3 sugars are known as gangliosides

Ganglioside Most complex glycosphingolipid

Waxes A complex mixture of esters of long -chain carboxylic acids (fatty acids) and alcohols Found as protective coatings for plants and animals

Steroids Steroids: a group of lipids that have fused-ring structure of 3 six-membered rings, and 1 five-membered ring. Most abundant steroid:cholesterol E.g.: vit D, estrogen, cortisone

Cholesterol The steroid of most interest in our discussion of biological membranes is cholesterol Amphiphilic – but more hydrophobic than glycerophospholipids and sphingolipids

Phytosterol Plant steroid

Vitamins E, K, -carotene Isoprenoids Based on isoprene structures Vitamins E, K, -carotene

Example isoprene

Eicosanoids Eicosanoids a family of compounds that have the 20-carbon skeleton Arachidonic acid as precursor Example: prostaglandins and leukotrienes

Lipid soluble vitamins

Lipid: Functions Storage molecules for energy Membrane components Messenger Mediate the hormonal responseand synthesis of hormones

Fluid-mosaic model