Ch. 20 Lipids Milbank High School

Objectives 1.How are lipids defined? How are they classified? 2.What is a fatty acid? What is the difference between a saturated, monounsaturated, and polyunsaturated fatty acid? 3.Why are fats and oils referred to as triglycerides (or triacylglycerols)? What determines if a triglyceride is a fat or oil? 4.What does the iodine number tell you about a triglyceride? 5.Why is it important for a soap to have both a hydrophilic and a hydrophobic end?

Objectives 6.What are the functions of phospholipids, glycolipids, and sphingolipids? What distinguishing characteristics are used to place lipids into one of these categories? 7.What are the major components of cell membranes and how are they arranged? 8.What are the functions of steroids? 9.What is the link between cholesterol, lipoproteins, and cardiovascular disease?

Lipids Fats and oils Twice the energy as carbs…but it usually goes into storage Uses other than energy: –Protection –Cell membranes –Fat soluble vitamins A, D, E, and K

Lipids Classified as a group based upon their solubility –INSOLUBLE in water Lipid: compound isolated from body tissues that is more soluble in organic solvents than in water Broad variations in structure

Sec Fatty Acids Carboxylic acids –Components of fats and oils Even number of carbon atoms Saturated fatty acids Monounsaturated fatty acids Polyunsaturated fatty acids

Fatty acids Con’t Use table 20.1 to answer the following questions: –Find an example of a: Saturated fatty acid Polyunsaturated fatty acid Monounsaturated fatty acid –Draw Myristic acid Oleic acid Linoleic acid

Sec Fats and Oils Most abundant lipids in nature Energy, protection, insulators “Triglycerides” –Esters composed of three fatty acids joined to glycerol, a trihydroxy alcohol –Fats if solid at 25°C –Oils if liquid at same temp

Fats and Oils Con’t Saturated fats –Cholesterol –Arteriosclerosis Use olive oil or canola oil –They lower LDL cholesterol –High percentage of monounsaturated fatty acids

Reactions of Fats and Oils Hydrolysis Hydrogenation Oxidation Antioxidants

Sec Soaps Saponification Second oldest organic synthesis (1 st is production of ethyl alcohol) Hydrolysis of triglycerides + sodium carbonate

How do soaps work? Figure 20.4 Hydrophilic (water soluble) Hydrophobic (repelled by water) Soaps don’t work well in hard water (soap scum) Detergent –Toothpaste!?!

Sec Membrane Lipids Phospholipids –Phosphoglycerides Glycolipids Sphingolipids Sphingomylelins –Cerebrosides –Gangliosides

Sec Cell Membranes Cytoplasm Micelles Bilayers Three major classes in the membrane bilayer of animal cells: –Phospholipids –Glycolipids –Cholesterol

Cell Membranes Two rows of phospholipid molecules –Tail to tail Semipermeable Integral proteins Peripheral Proteins

Sec Steroids: Cholesterol and Bile Salts Nonsaponifiable Bile salts, cholesterol, cortisone (hormone), sex hormones, and related compounds Must have 4 fused rings

Cholesterol Does not occur in plants Most abundant steroid in human body Biosynthesis of: –Sex hormones –Adrenal hormones –Vitamin D Excess cholesterol –Gall stones

Bile Produced in liver Bile salts –Aid in the digestion of dietary lipids –Aid in absorption of fatty acids, cholesterol, and fat-soluble vitamins Effective detergents and emulsifying agents

Sec Cholesterol and Cardiovascular Disease Primary factor in atherosclerosis, coronary artery disease, and stroke –41.5% of deaths nationwide –High cholesterol (over 260mg/100mL) –Males higher than females

Cholesterol Not soluble in water Cannot be transported in blood unless linked with a lipoprotein (water-soluble proteins) 4 types –Chylomicrons –Very low density (VLDL) –Low-density proteins (LDL) –High-density proteins (HDL) Contains least amount of lipid

Cholesterol High levels of LDL increase heart disease risk High HDL reduces heart risk –LDL:HDL ratio better indicator of heart disease risk

HDL Transport excess cholesterol from various tissues to the liver where it is metabolized Basically they are removing cholesterol from the blood Increase HDL by: –Exercise –Lose weight –Alcohol in moderation

Dietary Modifications Average American: 600 mg/day of cholesterol –Recommended: 300 mg/day –One large egg: 215 mg Integrate unsaturated fat for saturated fats –Omega-3 fatty acids –Fish oil –Reason? Polyunsaturated fatty acids

Atherosclerosis Most common form of arteriosclerosis (thickening of the arterial walls) LDL’s lodge in arteries, oxidized, white blood cells try to consume oxidized products, enlarged white blood cells accumulate, causes plaque that narrows arteries Most serious consequence: heart attack

Statins Inhibits the enzyme HMG-CoA reductase Inhibition of this enzyme in the liver stimulates LDL receptors, resulting in an increased clearance of low-density lipoprotein (LDL) from the bloodstream and a decrease in blood cholesterol levels. Lipitor, Crestor

Olestra Fat substitute, calorie free Synthesized using a sucrose molecole, which holds many fatty acids chains Molecule is too large to move through intestinal wall Olean May cause cramps and diarrhea

Heart Healthy Foods Top 25—see article Phytoestrogens –Flaxseed Phytosterols Carotenoids Polyphenols Omega-3 fatty acids B-Complex vitamins

Leptin Regulates energy intake and enery expenditure –Appetite and metabolism Regulated downward at night by melatonin Increased during pregnancy