University:
Glendale Community College
Course:
CHM152 | General Chemistry II
Academic year:

2021
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199

Pages:

21
Author:

hugdeigury7

Section 11.1: Lipid Classes Lipids classes: 1. Fatty acids 2. Triacylglycerols 3. Wax esters 4. Phospholipids 5. Sphingolipids 6. Isoprenoids Section 11.1: Lipid Classes Figure 11.1 Fatty Acid Structure §Fatty Acids §Monocarboxylic acids – carboxyl head; hydrocarbon chain tail §Even number of carbons – 12 - 20 §Numbered from the carboxylate end, a-carbon is adjacent to the carboxylate group §Terminal methyl carbon - omega (w) carbon §Hydrolysis of animal fats, vegetable oils or phosphdiacylglycerols of membranes §Functions: §Insulation – maintain body temperature §Energy storage – breakdown of fatty acids for molecules for energy production §Water repellent – fur, feathers Section 11.1: Lipid Classes Section 11.1: Lipid Classes Saturated versus unsaturated Fatty acids Section 11.1: Lipid Classes §Plants and bacteria – synthesize fatty acids from acetyl-CoA §Animals acquire most of theirs from dietary sources §Nonessential fatty acids – mammals can synthesize saturated FA & some unsaturated ones §Adding 2-C units & introducing double bonds §Essential fatty acids - acquired from the diet §Omega-3 fatty acids (i.e., a-linolenic acid and its derivatives) may promote cardiovascular health §Acylated proteins - fatty acids attached to protein § acyl groups help facilitate interactions with the environment §Myristoylation and palmitoylation Section 11.1: Lipid Classes Figure 11.4a Eicosanoids §Eicosanoids – prostaglandins, thromboxanes, leukotrienes §Mediate a wide variety of physiological processes: smooth muscle contraction, inflammation, pain perception, and blood flow regulation §Arachidonic acid – 20 carbon atoms, 4 double bonds §Precursor for all Section 11.1: Lipid Classes Figure 11.4a Eicosanoids §Prostaglandins (a) contain a cyclopentane ring and hydroxyl groups at C-11 and C-15 §Involved in inflammation, digestion, and reproduction §Thromboxanes (b) - cyclic ether, synthesized by platets §Involved in platelet aggregation, vasoconstriction following tissue injury §Leukotrienes (c) – linear with triene group (white blood cells) §Anaphylaxis (LTC4, LTD4, and LTE4) – severe allergic reaction §blood vessel fluid leakage, white blood cell chemo-attractant, vasoconstriction, edema, broncho-constriction Section 11.1: Lipid Classes §Triacylglycerols §Esters of glycerol with three fatty acids; neutral fats §Contain fatty acids of varying lengths - mixture of saturated and unsaturated §Accumulate in adipose tissue – storage §Lipases – hydrolyze ester linkages §Solid at room temperature; high saturated fatty acid composition §Liquid at room temperature; high unsaturated fatty acid composition From McKee and McKee, Biochemistry Section 11.1: Lipid Classes Saponification - natural soaps are prepared by boiling triglycerides (animal fats or vegetable oils) with NaOH § Soaps form water-insoluble salts when used in water containing Ca(II), Mg(II), and Fe(III) ions (hard water) § Reactions with acids/bases as catalysts § Glycerol – creams, lotions, nitroglycerin Section 11.1: Lipid Classes §Roles in animals: energy storage (also in plants), insulation at low temperatures, water repellent for some animals’ feathers and fur §Better energy storage form: 1. Hydrophobic - coalesce into droplets; store an equivalent amount of energy in about one-eighth the space 2. More reduced - can release more electrons per molecule when oxidized Section 11.1: Lipid Classes §Wax Esters §Composed of long-chain fatty acids and long-chain alcohols §Protective coatings - leaves, stems, fruits of plants; skin and fur of animals §Examples include myricyl cerotate (beeswax, carnauba wax); cetyl palmitate (spermaceti) From McKee and McKee, Biochemistry Section 11.1: Lipid Classes Figure 11.9 Phospholipid Molecules in Aqueous Solution §Phospholipids §Amphipathic - polar head (phosphate, other polar or charged groups); hydrophobic fatty acids (nonpolar tail) §Act in membrane formation, emulsification, and as a surfactant §Micelle - Spontaneously rearrange into ordered structures when suspended in water Section 11.1: Lipid Classes §Two types of phospholipids: §Sphingomyelins contain sphingosine instead of glycerol (also classified as sphingolipids) §Abundant in nervous system §Phosphoglycerides contain a glycerol, fatty acids, phosphate, an alcohol §Simplest - phosphatidic acid composed of glycerol-3-phosphate and two fatty acids §Phosphatidyl ethanolamine (cephalin) – brain & nerve tissue §Phosphatidylcholine (lecithin) – major part of membranes surrounding cells §Diphosphatidyl glycerol (cardiolipin) – inner mitochondrial membrane Section 11.1: Lipid Classes Figure 11.11 Phospholipases §Phospholipases- hydrolyze ester bonds in glycerophospholipid molecules §Three major functions §Membrane remodeling—adjust membrane flexibility or repair a damaged fatty acid §Signal Transduction—phospholipid hydrolysis initiates the signal transduction by numerous hormones § Digestion—pancreatic phospholipases degrade dietary phospholipids in the small intestine §Toxic Phospholipases—various organisms use membranedegrading phospholipases as a means of inflicting damage §Bacterial a-toxin and necrosis from snake venom (PLA2) Section 11.1: Lipid Classes §Sphingolipids - important components of animal and plant membranes §Ceramide – fatty acid linked to amino group of sphingosine (long-chain amino alcohol) §Abundant in nervous system §Sphingomyelin – primary alcohol group esterified to phosphoric acid esterified to amino alcohol §Abundant in the myelin sheath of nerve cells Section 11.1: Lipid Classes Figure 11.14a Selected Glycolipids Glycolipids §Carbohydrate bound to alcohol group of lipid by O-glycosidic bond §Glycosphingolipids – ceramide without P is parent compound §Most important classes §Cerebrosides have a monosaccharide for their head group §Galactocerebroside found in brain cell membranes §Sulfatides – sulfated cerebroside, negative charge at physiological pH §Gangliosides possess oligosaccharide groups; occur in most animal tissues and GM2 is involved in Tay-Sachs disease §Found as markers on cell membranes play a large role in tissue & organ specificity Section 11.1: Lipid Classes Figure 11.15 Isoprene §Isoprenoids - repeating five-carbon structural units (isoprene units) §Terpenes - classified by the number of isoprene units §Monoterpenes (used in perfumes), sesquiterpines (e.g., citronella), tetraterpenes (e.g., carotenoids) §Carotenoids are the orange pigments found in plants §Mixed terpenoids consist of a nonterpene group attached to the isoprenoid group (prenyl groups) §Include vitamin K and vitamin E Section 11.1: Lipid Classes §Steroids – derivative of terpenes, fused-ring structure of 3 6membered rings, 1 5-membered ring §Sex hormones – regulate development of primary and secondary sex charateristics §Testosterone – produced in testes, male characteristics §Estradiol – produced in ovaries, female characteristics §Progesterone – precursor for testosterone From McKee and McKee, Biochemistry, 5th Edition, © 2011 Oxford University Press Section 11.1: Lipid Classes §Cholesterol - classified as a sterol, because C-3 is oxidized to a hydroxyl group §Essential in animal membranes; a precursor of all steroid hormones, vitamin D, and bile salts §Usually stored in cells as a fatty acid ester §Highly hydrophobic §Atherosclerosis – blocked blood vessels Section 11.1: Lipid Classes Lipoproteins – protein covalently linked to lipid groups §Transport lipid molecules through bloodstream from organ to organ §Apolipoproteins – protein component are synthesized in liver or intestine §Five classes of apolipoproteins (A, B, C, D, and E) §Differentiated by types of lipoproteins with different ratios of lipid and protein components §Four clases of plasma lipotroteins Figure 11.21 Plasma Lipoproteins §Chylomicron, LDL, VLDL, HDL Section 11.1: Lipid Classes Lipoproteins are classified according to their density: §Chylomicrons - large lipoproteins; extremely low density; transport triacylglycerol and cholesteryl esters; synthesized in the intestines §Very low density lipoproteins (VLDL) - synthesized in the liver and transport lipids to the tissues §Low density lipoproteins (LDL) - principle transporters of cholesterol and cholesteryl esters to tissues §High density lipoprotein (HDL) - protein-rich particle produced in the liver and intestine; may be a scavenger of excess cholesterol from membranes §Scavenges excess cholesteryl esters that are produced by lecithin:cholesterol acetyltransferase §Transports to liver converted to bile acids §“Good cholesterol”