Chapter 10.1: Storage Lipids CHEM 7784 Biochemistry Professor Bensley

CHAPTER 10.1 Storage Lipids –Biological roles of lipids –Structure and properties of storage lipids Chapter Objectives: To understand the

Lipids: Structurally Diverse Class Low solubility in water Good solubility in nonpolar solvents

Classification of Lipids Based on the structure and function: 1. Lipids that contain fatty acids (complex lipids): Storage lipids and membrane lipids 2. Lipids that do not contain fatty acids: Cholesterol, terpenes, …

Lipid Subclasses

Fatty Acids Carboxylic acids with hydrocarbon chains containing from 4 to 36 carbons Almost all natural fatty acids have an even number of carbons Most natural fatty acids are unbranched Saturated: Monounsaturated: Polyunsaturated:

Common Saturated Fatty Acids common nameIUPAC namemelting point (C o ) 12:0lauratedodeconoate44 14:0myristatetetradeconoate52 16:0palmitatehexadeconoate63 18:0stearateoctadeconoate70 20:0arachidateeicosanoate75 22:0behenatedocosanoate81 24:0lignoceratetetracosanate84

Common Unsaturated Fatty Acids common nameIUPAC name melting point (C o ) 16:0palmitatehexadeconoate63 16:1  9 palmitoleate cis-  9 -hexadeconoate :0stearateoctadeconoate70 18:1  9 oleate cis-  9 - octadeconoate 13 18:2  9,12 linoleate cis-  9,12 - octadeconoate -9 18:3  9,12,15 linolenate cis-  9,12,15 - octadeconoate :0arachidateeicosanoate75 20:4  5,8,11,14 arachindonate cis-  5,8,11,14- eicosatetraenoate -49

Physical Properties and Conformation of Saturated Fatty Acids Solubility decreases as the chain length increases Melting point increases as the chain length increases The saturated chain tends to adopt extended conformations The double bonds in natural unsaturated fatty acids are commonly in cis configuration This introduces a kink in the chain

Melting Point and Double Bonds Saturated fatty acids pack in a fairly orderly way –extensive favorable interactions Unsaturated cis fatty acid pack less regular due to the kink –Less extensive favorable interactions It takes less thermal energy to disrupt disordered packing of unsaturated fatty acids: –unsaturated cis fatty acids have a lower melting point

Melting Points of Fatty Acids 18:0 18:1 18:3 70 o C 13 o C -17 o C

Trans Fatty Acids Trans fatty acids form by partial dehydrogenation of unsaturated fatty acids A trans double bond allows a given fatty acid to adopt an extended conformation Trans fatty acids can pack more regularly, and show higher melting points than cis forms

Triacylglycerols (fats and oils) Majority of fatty acids in biological systems are found in the form of triacylglycerols Triacylglycerols are the primary storage form of lipids (body fat) Triacylglycerols are less soluble in water than fatty acids due to the lack of charged carboxylate group Triacylglycerols are less dense than water: fats and oils float

Waxes Waxes are esters of long-chain saturated and unsaturated fatty acids with long-chain alcohols Insoluble and have high melting points Beeswax is a mixture of a large number of lipids, including esters of triacontanol, and a long-chain alkane hentiacontane