Chem 1152: Ch. 18 Lipids

Lipids Biomolecules defined in terms of solubility: Insoluble in water but soluble in nonpolar solvents. Waxy, greasy or oily compounds. Biological Functions: Energy Storage Structural component of cell membranes Signaling molecules Two major classes  Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Saponifiable Lipids Saponification: base hydrolysis of esters to produce carboxylic acid salt and alcohol Simple Lipids: Contain fatty acids and alcohols Complex Lipids: Contain multiple fatty acids, alcohol, something else Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Fatty Acids Building blocks of many lipids Long chain carboxylic acids Carboxyl group hydrophilic at physiological pH (7.4) Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Micelles In aqueous solutions, ionized fatty acids form spherical clusters Polar head is facing out towards water (hydrophilic) Long alkane chains associate in interior (hydrophobic) through weak dispersion forces Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Characteristics of Fatty Acids Straight chain (unbranched) carboxylic acids Comprised of 10-20 carbons Usually have even number of carbons Can be saturated or unsaturated Usually no other functional groups unsaturated saturated Unsaturated fatty acids usually contain double bonds in the cis configuration This creates kink or bend in chain that prevents unsaturated fatty acids from packing together closely unlike saturated fatty acids Results in weaker intermolecular forces, lower MP’s Usually liquid at room temp Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Properties of Unsaturated Fatty Acids The kink or bend in chain of unsaturated fatty acids prevents from packing together closely unlike saturated fatty acids Results in weaker intermolecular forces, lower MP’s Increases fluidity of biological membranes Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Properties of Unsaturated Fatty Acids Phospholipids form bilayer in cell membrane Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Essential Fatty Acids The human body can synthesize all but two of the necessary fatty acids Linoleic acid (omega-6 fatty acid) Linolenic acid (omega-3 fatty acid) Must be obtained from diet (plant and fish oils) Polyunsaturated (multiple double bonds) 18 Carbons in chain Diets rich in omega-3 fatty acids may: decrease serum cholesterol, triglycerides reduce risk of heart disease Sources of omega-3 fatty acids: Fish Nuts Kidney Beans Spinach Broccoli and cauliflower Oils Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Structures of Fats and Oils Fats: Triglycerides from animal (saturated) Oils: Triglycerides from vegetables (unsaturated) These are esters (alcohol + acid) Alcohol derived from glycerol Acid from fatty acids Most common lipids triglyceride Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Reactions of Triglycerides Ester of 3 alcohols, 3 acids triglyceride hydrogenation hydrolysis saponification Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Chemical Properties of Fats and Oils Triglycerides exhibit chemical properties of esters and alkenes Rxn: Hydrolysis Breakdown of cellular fats to supply energy begins with lipase catalyzed hydrolysis reaction Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Chemical Properties of Fats and Oils Rxn: Saponification Soapmaking (up to AD 500), by adding base (lye or aqueous extract of wood ash) to animal fat Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Chemical Properties of Fats and Oils Rxn: Hydrogenation Results in partial hydrogenation (partially-hydrogenated vegetable oils) Semi-solids that don’t separate  Crisco Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Waxes Simple, saponifiable lipids (long chain fatty acid + alcohol = ester) Alcohol derived from long chain alcohols (12-32 carbons) not glycerols Water insoluble Occur in nature as protective coatings on: Feathers Fur Skin Leaves Fruits Beeswax Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Phosphoglycerides Complex lipids Serve as major components of cell membranes Also known as phospholipids Structure similar to triglycerides triglyceride phosphoglyceride Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Phosphoglycerides The most common phosphoglycerides have choline, ehanolamine, or serine attached to the phosphate group. Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Phosphatidylcholine (lecithin) Phosphoglycerides Lecithins Phospholglycerides that contain choline Soy lecithin used to provide smooth texture to margarine, chocolate Cephalins Phospholglycerides that contain ethanolamine or serine Functions: structural components of cell membranes micelle forming agents Functions: Cell membranes Blood-clotting Phosphatidylcholine (lecithin) Cephalin Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Sphingolipids Complex lipid found in cell membrane Contain sphingosine instead of glycerol These are found in brain and nerve tissue, and in myelin sheath that surrounds nerves Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Glycolipids Another type sphingolipid Contain carbohydrates AKA cerebrosides due to abundance in brain tissue No phosphate linkage Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Related Diseases Some human diseases are related to abnormal accumulation of sphingomyelins and glycolipids Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Fluid-mosaic Model of Biological Membranes Cell membranes for both prokaryotic and eukaryotic cells comprised of lipids organized in a bilayer Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Steroids Exhibit feature of other lipids (e.g., soluble in non-polar solvents) Cholesterol is most abundant steroid in human body Essential component of cell membranes Precursor for other steroids: Bile salts Sex hormones Vitamin D Adrenocorticoid hormones Synthesized in liver or obtained from food May contribute to atherosclerosis Steroid Cholesterol Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Bile Salts Yellow-brown or green liver secretion stored in gallbladder Bile salts are released into intestine to separate large globules of lipids into smaller droplets Bile salts also emulsify (mix immiscibles) cholesterol found in the bile for excretion Gallstones may occur if cholesterol too high and/or bile salts too low Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011; http://www.medicinenet.com/gallstones/article.htm

Steroid Hormones Hormone: Chemical produced in the cell or gland that delivers a message affecting cells in another part of the organism Steroid hormones derived from cholesterol Two Major Steroid Hormones: Adrenocorticoid Hormones Male and Female Sex Hormones Steroid hormones diffuse through the cell membrane and combine with receptor proteins in the cytoplasm Hormone-receptor complex cause cell to respond to hormone by interacting with cell DNA and stimulating protein synthesis http://schoolworkhelper.net/2010/07/the-endocrine-system-function-and-structure/

Adrenocorticoid Hormones Produced in adrenal glands located at top of kidneys Classified into 2 functional groups: Mineralocorticoids: Regulate concentration of ions (Na+) in body fluids Aldosterone: most important mineralocorticoid Promotes absorption of Na+ and Cl- in kidney tubules Glucorticoids: Enhance carbohydrate metabolism Cortisol is major glucocorticoid in human body Increases glucose and glycogen concentration in body Cortisol, cortisone and prednisolone exert anti-inflammatory effects Used to treat rheumatoid arthritis, bronchial asthma Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Male Sex Hormones Male sex hormones (androgens) produced in testes Testosterone: Most important Promotes normal growth of male genitalia and aids in development of secondary sex characteristics Anabolic steroids banned for use by athletes include testosterone and derivatives Use of these can lead to: Liver tumors Testicular atrophy Decreased sperm count Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011; http://artofamandanelson.blogspot.com/2011/09/generating-topics-steroids.html

Female Sex Hormones Female sex hormones promote development of secondary sex characteristics Increase in voice pitch Increased breast size Inhibition of facial hair Estrogens: Primary female sex hormones, play important roles in reproduction: Estradiol Estrone Progesterone Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Prostaglandins First identified in secretions from male prostate gland Currently about 20 known prostaglandins in both men and women Cyclic compounds derived from arachidonic acid Hormone-like Functions: Regulate menstruation Prevent conception Induce uterine contractions during childbirth Therapeutic applications: Induce labor Treat asthma Treat peptic ulcers Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011