LIPIDS Chemical Structure and Biological Function

1. Principles of Biochemistry (BCH 3000) LIPIDS Chemical Structure and Biological Function Dr. Syahida Ahmad Department of Biochemistry Faculty of Biotechnology & Biomolecular Sciences UPM

3. Lipids • Characterize on their solubility behavior • Hydrophobic nature - more soluble in nonpolar solvents (alcohol, diethyl ether, MeOH and hexane) than in water • Chemical functional groups • Carbon-carbon single and double bonds, aldehydes and ketones, carboxylate esters, phosphate esters, amines and amides • Main role in energy metabolism • Long-term energy storage • Fatty acids • Components of nonpolar lipids (fats) • Important energy molecules in heart, brain and adipose tissues • Biological membrane • Polar lipids containing N and P • Composed primarily of lipids and proteins – molecular boundaries around all cells and cell organelles • Steroid • Class of lipids that represented by cholesterol – found in membranes and also serve as precursor for many hormones

4. Fatty Acids • Contain carboxyl group (-COOH)connected to an unbranched aliphatic chain • Amphiphilic – one end is polar/ ionic (the carboxyl group), opposite end (the hydrocarbon chain) has polar properties • Bound in fats(triacylglycerols and other lipids) • Hydrocarbon chain with number of carbon atoms range 4-36 • unbranched • Saturated fatty acids – carbon-carbon single bonds • Unsaturated fatty acids - carbon-carbon double bonds • Polyunsaturatedfatty acids– two or more double bonds • Cis configuration • Lauric acid (dodecanoic acid) or 12:0 • Fatty acid with 12-C atoms and no double bonds • Linoleic acid or 18:2 (∆) 9,12 • Fatty acid with 18-C atoms and two double bonds (C9-C10 and C12-C13)

9. Triacylglycerol • Nonpolar lipids • Very hydrophobic and serve as storage molecules for metabolic fuel • All fatty acids present in nature are found as constituents of the triacyglycerols • Glycerol – trihydroxyl (-OH) compound(basic foundation molecule) • Each –OH group can be linked to a fatty acid by esterification • Fats • Solids triacylglycerols isolated from animal tissues • Contain predominantly saturated fatty acids • Oils • Liquid triacylglycerols isolated from plant seeds • Contain predominantly unsaturated fatty acids • Waxes • Protective coatings for plant leaves • Beeswax, an ester composed of palmitic acid (16:0) and alcohol triacontanol (saturated chain of 30-C)

10. Question: __________ are the subunits of fats and oils. Answer: Fatty acids and glycerol

11. Question: There is a direct link between ___________ fats and heart disease. Answer: saturated

14. Triacylglycerol Reactivity Triacylglycerol Reactivity • Ester Hydrolysis • Saponification – hydrolysis of ester by NaOH to produce glycerol and soaps • Lipase – enzymes present in intestines and in fat cells (adipocytes) to release fatty acids for energy metabolism • Partial Hydrogenation • Use to reduce the number of double bonds in the fatty acids – to change oil into a firm, but spreadable solid like“soft” margarine • Ester Hydrolysis • Saponification – hydrolysis of ester by NaOH to produce glycerol and soaps • Lipase – enzymes present in intestines and in fat cells (adipocytes) to release fatty acids for energy metabolism • Partial Hydrogenation • Use to reduce the number of double bonds in the fatty acids – to change oil into a firm, but spreadable solid like“soft” margarine

21. Polar Lipids • Amphiphilic (dual nature)– have both nonpolar and polar structure • Allows them to combine with protein molecules for the construction of biological membranes (around cells and cellular organelles) • Membrane • Permeable barrier that selects some molecules for passage but not others • Bilayers – two monolayers or sheets of polar lipids • Glycerophospholipids • Sphingolipids • Amphiphilic (dual nature)– have both nonpolar and polar structure • Allows them to combine with protein molecules for the construction of biological membranes (around cells and cellular organelles) • Membrane • Permeable barrier that selects some molecules for passage but not others • Bilayers – two monolayers or sheets of polar lipids • Glycerophospholipids • Sphingolipids

28. Question Which ONE of the following forms the structural basis for cell membranes? waxes micelles gamma globulin fatty acid triacylglycerol

29. Steroids and Other Lipids • Animal Steroids – Cholesterol • Hormones (estradiol, testosterone and cortisol) • Phytosterols • Cholesterol found in plants (stigmasterols, -sitosterols and campesterol) • Terpenes • In plants and animals (limonene, -carotene, gibberellic acid, squalene and lycopene) • provide colors and odors associated with plants • Eicosanoids • Short-lived hormone like activities (prostaglandins, thromboxanes and leukotrienes) • Lipid-Soluble Vitamins • A, D, E and K • Pheromones • Chemical signals release by organisms into the environment that alter the behavior of members of the same species or of organisms they interact with • For sexual attraction, trail markings and defense alarms (natural repellants)

33. Question Which ONE of the following is the most abundant steroid? Testosterone Estrogen progesterone cholesterol prostanoid