What is Lipid Lipids: 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 1.Open chain: – long nonpolar tail with a polar head – Saponifiable 2.Cyclic forms/Fused ring: - based on the steroid ring skeleton

1.Fatty acids and their derivatives 2.Triacylglycerols 3.Phosphoacylglycerol, phosphoglycerides 4.Sphingolipids 5.Wax esters 6.Isoprenoids (based on isoprene structure) LIPID: CLASSESS

LIPID: Structural features 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 GENERAL STRUCTURE / phosphoacylglycerol

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

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

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 Cis double bond results in a bent chain and lower mp. Palmitoleic acid 16:1  9

Fatty Acids Palmitoleic 16:1  9 – degree of unsaturation or abbreviation symbol CH 3 (CH 2 ) 5 CH=CH (CH 2 ) 7 COOH – chemical formula Palmitoleic acid

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

Fatty Acids

Fatty Acids - examples 1.Stearic 18:0 CH 3 (CH 2 ) 16 COOH 2.Oleic acid 18:1  9 / 18:1  9 / 18:1-  9 CH 3 (CH 2 ) 4 CH 2 CH 2 CH 2 CH=CH(CH 2 ) 7 COOH 3.Palmitoleic16:1  9 CH 3 (CH 2 ) 5 CH=CH (CH 2 ) 7 COOH 4.Linolenic 18:2  9,12 CH 3 (CH 2 ) 4 CH=CHCH 2 CH=CH(CH 2 ) 7 COOH 5.Arachidonic20:4  5,8,11,14 CH 3 (CH 2 ) 3 (CH 2 CH=CH) 4 (CH 2 ) 3 COOH

Triacylglycerols 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 NaOH or KOH to produce soap, which is the sodium salt

Phosphoacylglycerols (Phospholipids) When group of is rather than by a carboxylic acid, phosphatidic acid produced When one alcohol group of glycerol is esterified by a phosphoric acid rather than by a carboxylic acid, phosphatidic acid produced Phosphatidyl ester = phosphoacylglycerol Phosphoacylglycerol – the phosphoric acid (in phosphatidic acid) is esterified to second alcohol Phosphatidic acid

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

Phosphatidyl esters = phosphoacylglycerol = glycerophospholipids Fatty acid

Sphingolipids No glycerol Contain sphingosine, a long-chain amino alcohol Found in plants and animals 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 Glycolipid: 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 glycosphingolipid

Ganglioside Most complex glycosphingolipid

 Salts of fatty acid with polar head and a single nonpolar assemble into spherical structures - micelles 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 Phospholipids

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: Steroids: a group of lipids that have fused-ring structure of 3 six-membered rings, and 1 five-membered ring.

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

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

Example isoprene

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

Lipid soluble vitamins

1.Storage molecules for energy 2.Membrane components 3.Messenger 4.Mediate the hormonal responseand synthesis of hormones Lipid: Functions