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HL Chemistry - Option B: Human Biochemistry

HL Chemistry - Option B: Human Biochemistry. Lipids. Part 1. Overview of Lipid Categories. Lipids: Two Major Categories. Lipids are generally categorized as either saponifiable or non-saponifiable

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HL Chemistry - Option B: Human Biochemistry

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  1. HL Chemistry - Option B: Human Biochemistry Lipids

  2. Part 1 Overview of Lipid Categories

  3. Lipids: Two Major Categories • Lipids are generally categorized as either saponifiableor non-saponifiable • Saponifiable lipids are formed from the reaction of glycerol (1,2,3-propanetriol) and long chain carboxylic acids (fatty acids) • Saponifiable lipids can be cleaved by sodium hydroxide to form glycerol and 3 moles of soap (the salts of long chain fatty [carboxylic] acids)

  4. Other Important Facts • Lipids are water insoluble compounds • Most lipids are in fact saponifiable • They are soluble in non-polar solvents such as petroleum ether, benzene, chloroform • Functions • Energy storage • Structure of cell membranes • Thermal blanket and cushion • Non-saponifiable lipids are precursors of hormones (steroids and prostaglandins) • Types or components of saponifiable lipids: • Fatty acids • Neutral lipids • Phospholipids and other lipids

  5. Neutral Lipids • Glycerides (fats and oils) • Glycerol • Ester of glycerol - mono glycerides, diglycerides and triglycerides • Waxes – simple esters of long chain alcohols

  6. GLYCERIDES Function: storage of energy in compact form

  7. Saponification Reactions Produce Glycerol and Soap

  8. Esterification Reactions Produce “Fat”

  9. Analytical Methods to Evaluate Saponifiable Lipids • Saponification Number • Iodine Value (Hanus Method) [This is the method we will concentrate on] • Free Fatty Acids • Acetyl Number • Reichert-Meissl number • HPLC/GC (for more precise analysis)

  10. Iodine Number • Measures the degree of unsaturation in a given amount of fat or oil • The iodine number is the number of grams of iodine absorbed by 100 grams of fat • Cottonseed oil: 103 –111 • Olive oil: 79 – 88 • Linseed oil: 175 –202 • Frequently used to determine contamination of commercial lots of oils

  11. Sample Iodine Calculation #1 Question: 0.01 moles of linoleic acid reacts with 5.1 g of iodine. Determine the number of double bonds present in the acid. Answer: Moles iodine = (5.1 grams)(1 mole iodine / 254 grams of iodine) = 0.020 moles I2 This implies a ratio of 0.01 mol linoleic acid : 0.020 mole I2 Therefore, Every molecule of linoleic acid contains 2 double bonds

  12. Sample Iodine Calculation #2 Question: Calculate the iodine number of linoloeic acid, C17H31COOH. Answer: Molecular Weight of Acid = 18(12) + 32(1) +2(16) = 280 g/mol Molecular Weight of Iodine = 2(127) = 254 g/mol Linoleic Acid has 2 double bonds per molecule (from last problem). 280 grams of fat reacts with 2 x 254 g of iodine = 508 g iodine 100 grams of fat reacts with 508/280 = 181 The iodine number of linoleic acid is 181

  13. Part 2 Fatty Acids

  14. Fatty Acids • Fatty acids are carboxylic acid derivatives of long chain hydrocarbons • Nomenclature (somewhat confusing) • Stearate – stearic acid – C18:0 – n-octadecanoic acid • General structure:

  15. Some Common Fatty Acids Common Fatty Acids n = 4 butyric acid (butanoic acid) n = 6 caproic acid (hexanoic acid) n = 8 caprylic acid (octanoic acid) n = 10 capric acid (decanoic acid) n = 12: lauric acid (n-dodecanoic acid; C12:0) n = 14: myristic acid (n-tetradecanoic acid; C14:0) n = 16: palmitic acid (n-hexadecanoic acid; C16:0) n = 18; stearic acid (n-octadecanoic acid; C18:0) n = 20; arachidic (eicosanoic acid; C20:0) n= 22; behenic acid n = 24; lignoceric acid n = 26; cerotic acid

  16. Fatty Acid Classification • Fatty acids can be classified either as: • (1) saturated or unsaturated • (2) according to chain length: • short chain FA: 2-4 carbon atoms • medium chain FA: 6 –10 carbon atoms • long chain FA: 12 – 26 carbon atoms • essential fatty acids vs. those that can be biosynthesized in the body: • linoleic and linolenic are two examples of essential fatty acid

  17. Monounsaturated Fatty Acids Monoenoic acid (monounsaturated) Double bond is always cis in natural fatty acids. This lowers the melting point due to “kink” in the chain

  18. Diunsaturated Fatty Acids Dienoic acid: (linoleic acid)

  19. Polyunsaturated Fatty Acids Polyenoic acid (polyunsaturated)

  20. Unsaturated Fatty Acid Examples Monoenoic acids (one double bond): • 16:1, 9 w7: palmitoleic acid (cis-9-hexadecenoic acid • 18:1, 9 w9: oleic acid (cis-9-octadecenoic acid) • 18:1, 9 w9: elaidic acid (trans-9-octadecenoic acid) • 22:1, 13 w9: erucic acid (cis-13-docosenoic acid) • 24:1, 15 w9: nervonic acid (cis-15-tetracosenoic acid)

  21. Hydrogenated Fatty Acids • Hydrogenation leads to either saturated fats and/or trans fatty acids • The purpose of hydrogenation is to make the oil/fat more stable to oxygen and temperature variation (increase shelf life) • Examples of hydrogenated fats: Crisco, margarine

  22. Other Facts about Fatty Acids • Soap, the salt of a fatty acid, reacts with divalent metal ions such as Ca+2 and Mg+2 in water • This reaction produces a precipitate commonly called “soap scum” • The way to remove soap scum is to chelate (combine or complex) the metal ions with chemicals (ligands) such as EDTA (ethylenediaminetetraacetic acid) • Detergents with phosphates resolubilize the soap scum, but poison the environment

  23. Micelles • Micelles can form from fatty acids or soaps • They are spherically shaped masses with the polar head groups facing the water and the non-polar tails facing inward

  24. Fatty Acid Reactions • salt formation • ester formation • lipid peroxidation

  25. Part 3 Fats, Oils, and Waxes

  26. Fats vs. Oils • Fats are solids or semi solids • Oils are liquids • Melting points and boiling points are not usually sharp (most fats/oils are mixtures) • When shaken with water, oils tend to emulsify • Pure fats and oils are colorless and odorless (color and odor is always a result of contaminants) – i.e. butter (bacteria give flavor, carotene gives color)

  27. Examples of Oils Olive oil – from Oleo europa (olive tree) Corn oil – from Zea mays Peanut oil – from Arachis hypogaea Cottonseed oil – from Gossypium Sesame oil – from Sesamum indicum Linseed oil – from Linum usitatissimum Sunflower seed oil – from Helianthus annuus Rapeseed oil – from Brassica rapa Coconut oil – from Cocos nucifera

  28. WAXES • Waxes are simple esters of fatty acids (usually saturated with long chain monohydroxy alcohols) Beeswax – also includes some free alcohol and fatty acids Spermaceti – contains cetyl palmitate (from whale oil) –useful for pharmaceuticals (creams/ointments; tableting and granulation) Carnauba wax– from a palm tree from brazil – a hard wax used on cars and boats

  29. Common Alcohols in Waxes Structure of Cetyl Alcohol

  30. Spermaceti source Carnauba wax source Bee’s wax

  31. Part 3 A Few Saponifiable Lipid Derivatives

  32. Phospholipids • The major components of cell membranes • phosphoglycerides Phospholipids are generally composed of fatty acids, a nitrogenous base, phosphoric acid and either glycerol, inositol or sphingosine

  33. Glycolipids There are different types of glycolipids: cerebrosides, gangliosides, and lactosylceramides

  34. Blood Groups Determined by various glycolipids on red blood cells A antigens B antigens H antigens (found on type O blood cells) (not recognized by anti-A or anti-B antibodies)

  35. Part 3 Nonsaponifiable Lipids

  36. Cholesterol and Cholesterol Esters

  37. STEROID NUMBERING SYSTEM

  38. STEREOCHEMISTRY OF STEROIDS

  39. Cholesterol Sources, Biosynthesis and Degradation • Diet: only found in animal fat • Biosynthesis: primarily synthesized in the liver from acetyl-coA; biosynthesis is inhibited by LDL uptake • Degradation: only occurs in the liver

  40. Cholesterol and Cholesterol Esters The hydroxyl at C-3 is hydrophilic; the rest of the molecule is hydrophobic; also 8 centers of asymmetry

  41. Cholesterol and Cholesterol Esters Functions: -serves as a component of cell membranes (increases or moderates membrane fluidity -precursor to steroid hormones -storage and transport – cholesterol esters

  42. Steroids as Hormones • Steroids act as chemical messengers. They are produced in the endocrine glands and are regulated by the pituitary gland (which is in turn regulated by the hypothalamus) • Since they are chemical in nature, steroids act slower than the nervous system • Hormones have a negative feedback system • Effective in very small amounts, and only targets specific cells

  43. Cholesterol vs. Sex Hormones • Cholesterol (top) is the building block of sex hormones, and even Vitamin D • Sex hormones such as testosterone (bottom) give males their sexual characteristics

  44. More Sex Hormones • Other male sex hormones such as androsterone (left) are related to the female hormone progesterone (right - maintains the uterus & developing embryo)

  45. The Female Reproductive Cycle • At the start of the menstrual cycle the pituitary gland releases follicle stimulating hormone (FSH) • FSH goes to the ovaries and causes oestradiol to prepare release of the egg and thickening of the uterine wall • After about 2 weeks FSH productions stops (feedback mechanism) and luteinizing hormone (LH) is produced • LH travels to the ovaries and stimulates production of progesterone • Progesterone causes the egg to travel to the uterus and the uterine wall to continue building • If the egg is not fertilized menstruation begins – this washes away the egg and the uterine lining • If the egg is fertilized it embeds itself in the uterine wall and overall hormone level rise dramatically

  46. Female Birth Control Pills • A combination of estrogen & progesterone (the “pill”) stops ovulation and mimics the biochemistry of a pregnant woman • This mixture of these hormones can cause irregular menstrual flow • New synthetic hormones such as norethindrone and norethynodrel reduce these problems • The “minipill” is active for 5 years and placed under the skin – it contains progestin, a hormone that changes the mucus of the uterus and makes it resistant to sperm

  47. Modern Birth Control Pill HormonesNorethindrone Norethynodrel

  48. Use & Abuse of Steroids • Testosterone can be used to help cancer patients build up muscle mass • Athletes can also abuse steroids as performance enhancing agents (urine tests detect steroids) • In aging males, steroids help baldness, urination problem, and ED • In women, male hormones lead to secondary male characteristics • Steroids also cause violent tempers, high blood pressure, liver tumors, and heart attacks • Oral steroids produce greater side effects than injected steroids

  49. Prostaglandins and other Eicosanoids • Prostaglandins (PGE) act as local hormones; they are unstable, and are the key mediators of inflammation • They are derivatives of prostanoic acid

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