1. Biomolecules Survey Part 2: Lipids Lecture Supplement page 228 Myricyl cerotate Present in beeswax, carnauba wax

2. Nonpolar: Hydrophobic (“water hating”) or lipophilic (“fat loving”) Polar: Hydrophilic (“water loving”) or lipophobic (“fat hating”) Found mostly in fatty tissues, membranes, and other nonpolar biological structures Lipids Definitions Lipid (Greek: lipos, fat): Organic molecule of biological origin that is insoluble in water and soluble in nonpolar solvents (CH 2 Cl 2, CH 3 CH 2 OCH 2 CH 3, etc.) Example: A phospholipid Lipid solubility properties due to large nonpolar regions

3. Lipids Eight General Categories Fatty acidsWaxesTriacylglycerides PhospholipidsSteroidsProstaglandins Lipophilic vitamins Terpenes Produced mostly by plants Not discussed in Chem 14C

4. Fatty Acids Fatty acid : Carboxylic acid with ‘long’ unbranched hydrocarbon chain Saturated fatty acids Lauric acid (12 C) Myristic acid (14 C) Palmitic acid (16 C) Stearic acid (18 C) Arachidic acid (20 C) Most have even number of carbons: Two carbons added at a time during biosynthesis 12-20 carbons most common Most biologically-important fatty acids have 18 carbons: Stearic, oleic, and linoleic acids Main biological function: Precursor to other lipids Categorized by C=C in chain: Saturated (no C=C) or unsaturated (one or more C=C)

5. Fatty Acids Monounsaturated : Contains one C=C Polyunsaturated : Contains more than one C=C Cis C=C much more common than trans C=C Linoleic acid (C 18 )Linolenic acid (C 18 ) Unsaturated fatty acids Some important unsaturated fatty acids Arachidonic acid (C 20 ) Cis alkene Common in fatty acids Trans alkene Rare in fatty acids Oleic acid (C 18 )

6. remove H 2 O Waxes Most natural waxes are esters derived from a fatty acid and a long-chain alcohol Example: Main biological function of waxes: Water barrier Myricyl cerotate Present in beeswax, carnauba wax Cerotic acid A fatty acid Myricyl alcohol Long chain alcohol Feathers Wax minimizes wetting Leaves Wax minimizes water evaporation

7. Triacylglycerols Triacylglycerol (triacylglyceride) : Fatty acid triester of glycerol (glycerin) Triacylglycerol = fat if solid at room temperature; oil if liquid The most abundant of the natural lipids Main biological function: Energy storage Hydrolysis (“water breaking”) of animal fats yields soap - 3 H 2 O mixture = soap Glycerol Fatty acids NaOH, H 2 O heat Triacylglycerol

8. Hydrophobic tails dissolve in nonpolar “dirt” dirt Triacylglycerols How Does Soap Work? Hydrophilic CO 2 - groups attracted to  + H-O-H  + Nonpolar (hydrophobic) hydrocarbon chains avoid water Nonpolar (lipophilic) hydrocarbon chains attracted to nonpolar “dirt”, other fatty acid chains Forms micelles (~spherical aggregates); suspends “dirt” in water Micelles carry dirt away when wash water is removed Micelle dirt Hydrophobic tail Hydrophilic CO 2 - Free soap molecules in H 2 O

9. Hydrophilic head Hydrophobic tail Triacylglycerols Soaps Hard water: Contains high levels of Fe 3+, Mg 2+, Ca 2+ Fatty acid salts of Fe 3+, Mg 2+, Ca 2+ have low water solubility Results in precipitates: Dull clothes, “bathtub ring” Solution: Synthetic soaps Good water solubility of Fe 3+, Mg 2+, Ca 2+ sulfonates Avoids dependency on animal fats (expensive; uncertain supply) Sodium 4-dodecylbenzenesulfonate Typical synthetic soap Soap problems and solutions

10. Phosphate ester Fatty acid esters Phospholipids Phospholipid : Glycerol esterified with two fatty acids and one phosphate group Phospholipid fatty acids usually palmitic acid, stearic acid, and/or oleic acid Second most abundant group of natural lipids Main biological function: Cell membranes (phospholipid bilayer) Generic phospholipid structure Hydrophobic effect : Hydrophobic tails avoid water

12. Mayonaisse – Oil and Vinegar An example of a phosphatidylcholine, a type of phospholipid in lecithin. Red - choline and phosphate group Black – glycerol Green - unsaturated fatty acid; Blue - saturated fatty acid Oil Vinegar or Lemon Juice Egg!!! Lecithin

13. Lower chain: eight carbons Upper chain: seven carbons Prostaglandins Prostaglandin: Molecule having the prostanoic acid skeleton Prostanoic acid Prostaglandin F 2  (PGF 2  ) Nomenclature: Based on stereochemistry, number of OH, C=C, C=O groups Biological functions: Mostly as regulators and signal molecules - cause constriction or dilatation in vascular and other smooth muscle cells - regulate aggregation and disaggregation of platelets - sensitize spinal neurons to pain - regulate inflammatory mediation, calcium movement, hormones - control cell growth

14. Prostaglandins Biological origin: Prostaglandin cascade May occur at wound site, leading to inflammation In vivo half-life typically 5 minutes or less Similar structures but wide range of functions

15. Steroids Steroid : A molecule having the ring system shown below Steroid skeleton AB C D Steroid example: Cholesterol Shape: Core is approximately flat Verify and explore with a model

16. Steroids Categories and Examples Sex hormones: Corticoid hormones: Testosterone (an androgen) Estrone ( an estrogen) Cortisone A glucocorticoid hormone Regulates inflammation Regulates glucose metabolism Aldosterone A mineralocorticoid hormone Regulates Na + /K + balance Synthesized in the adrenal complex Regulate metabolic processes

17. Steroids Categories and Examples Bile acids: Cholic acid Aid in digestion by emulsifying fats in intestine Steroids have similar structures but wide range of functions

18. Steroid Biosynthesis More than sixty steps from acetyl CoA  cholesterol many enzyme steps Acetyl CoA Lanosterol Cholesterol Biological precursor to all other vertebrate steroids Squalene epoxidase SqualeneSqualene oxide Squalene oxidocyclase 25 additional enzymatic steps

19. Lipophilic Vitamins Vitamin : An organic compound, other than fat, protein, or carbohydrate, required for the normal growth and maintenance of animals Broad range of structures and functions Vitamin E Mixture of stereoisomers;  -tocopherol most important Protects against oxidative damage to cells from radicals Vitamin C (ascorbic acid) Hydrophilic antioxidant vitamin Not a lipid  -Tocopherol Hydrophobic antioxidant vitamin

20. Lipophilic Vitamins Vitamin A (retinol) Essential to vision Incorporated into rhodopsin (photon-harvesting protein) An answer to the question “Do we have to memorize all of these structures?” Expected skills: Categorize a structure according to its lipid category Draw generic examples from each lipid category