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HL Chemistry - Option B : Human Biochemistry

HL Chemistry - Option B : Human Biochemistry. Lipids. Lipids: Two Major Categories. Lipids are generally categorized as either saponifiable or non-saponifiable Saponifiable lipids are formed from the reaction of glycerol (1,2,3-propanetriol) and long chain carboxylic acids (fatty acids)

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HL Chemistry - Option B : Human Biochemistry

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  1. HL Chemistry - Option B : Human Biochemistry Lipids

  2. Lipids: Two Major Categories • Lipids are generally categorized as either saponifiable or 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)

  3. Esterification reactions produces fat

  4. Saponification reactions produces glycerol and soap

  5. Other Important Facts • Lipids are water insoluble compounds • Most lipids are 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

  6. FATTY ACIDS

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

  8. 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)

  9. Fatty acids • common FA’s: 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

  10. Fatty acids • Fatty acids can be classified either as: • saturated or unsaturated • 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

  11. Unsaturated 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

  12. Unsaturated fatty acids • Dienoic acid: linoleic acid

  13. Unsaturated fatty acids • Polyenoic acid (polyunsaturated)

  14. Unsaturated fatty acids • 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)

  15. Typical fish oil supplements

  16. 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 • Detergents with phosphates resolubilize the soap scum and poison the environment

  17. 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

  18. FATS & OILS

  19. 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)

  20. 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

  21. Fatty acid reactions • salt formation • ester formation • lipid peroxidation

  22. Hydrogenated fats • 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

  23. OTHER SAPONIFIABLE LIPIDS (and their components)

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

  25. GLYCERIDES Function: storage of energy in compact form

  26. WAXES • simple esters of fatty acids (usually saturated with long chain monohydric 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

  27. Spermaceti source Carnauba wax source Bee’s wax

  28. Waxes Examples of long chain monohydric alcohols found in waxes

  29. Analytical methods to evaluate lipids

  30. Analytical methods to evaluate lipids • saponification number • iodine value (Hanus method) • free fatty acids • acetyl number • Reichert-Meissl number • HPLC/GC (for more precise analysis)

  31. 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

  32. 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.

  33. 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.

  34. Saponifiable Lipid Derivatives

  35. Phospholipids • the major components of cell membranes • phosphoglycerides Phospholipids are generally composed of FAs, a nitrogenous base, phosphoric acid and either glycerol, inositol or sphingosine

  36. glycolipids There are different types of glycolipids: cerebrosides, gangliosides, lactosylceramides

  37. Blood groups determined by various glycolipids on RBC’s A antigens B antigens H antigens (found on type O blood cells) not recognized by anti-A or anti-B antibodies

  38. Non-Saponifiable Lipids

  39. Cholesterol and cholesterol esters

  40. STEROID NUMBERING SYSTEM

  41. STEREOCHEMISTRY OF STEROIDS

  42. 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

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

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

  45. 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, they act slower than the nervous system. • Hormones have a negative feedback system. • Effective in very small amounts, and only targets specific cells.

  46. 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 characterstics

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

  48. 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 • I the egg is fertilized it embeds itself in the uterine wall and overall hormone level rise dramatically

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