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Lipid Structure and Function

Lipid Structure and Function. Common Physical Properties of Lipids. Soluble in non-polar organic solvents Contain C, H, O Sometimes N & P Includes fats and oils – mostly triglycerides Fat: solid at room temperature Oil: liquid at room temperature More highly reduced than CHO

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Lipid Structure and Function

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  1. Lipid Structure and Function

  2. Common Physical Properties of Lipids • Soluble in non-polar organic solvents • Contain C, H, O • Sometimes N & P • Includes fats and oils – mostly triglycerides • Fat: solid at room temperature • Oil: liquid at room temperature • More highly reduced than CHO • 2.25x more energy

  3. Lipids or Glucose for Energy? Energy-Containing Nutrients H+ ATP Electron Transport Chain CO2 O2 H2O

  4. More reduced state  More potential for oxidation Less reduced state  Less potential for oxidation Lipids or Glucose for Energy?

  5. Energy from Lipids • Compared to carbohydrates, fatty acids contain more hydrogen molecules per unit of carbon, thus, they are in a more reduced form • Carbohydrates are partially oxidized so they contain less potential energy (H+ and e-) per unit of carbon

  6. Functions and Properties • Concentrated source of energy (9 kcal/gm) • Energy reserve: any excess energy from carbohydrates, proteins and lipids are stored as triglycerides in adipose tissues • Provide insulation to the body from cold • Maintain body temperature • Mechanical insulation • Protects vital organs

  7. Functions and Properties • Electrical insulation • Protects nerves, help conduct electro-chemical impulses (myelin sheath) • Supply essential fatty acids (EFA) • Linoleic acid and linolenic acid • Formation of cell membranes • Phospholipids, a type of fat necessary for the synthesis of every cell membrane (also glycoproteins and glycolipids)

  8. Functions and Properties • Synthesis of prostaglandins from fatty acids • Hormone-like compounds that modulates many body processes • Immune system, nervous systems, and GI secretions • Regulatory functions: lower BP, blood clotting, uterine contractions • Help transport fat soluble vitamins • Palatability and aroma • Flavor and taste for some species! • The satiety value – help control appetite • Fullness; fats are digested slower • Regulated through gastric inhibitory protein (GIP) and cholecystokinin (CCK)

  9. Physical Traits of Fatty Acids • Form membranes, micelles, liposomes • Orient at water:oil interface • Contain hydrophobic and hydrophilic groups • Lipid bilayer for membranes • Micelles formed during digestion

  10. Physical Traits of Fatty Acids • Fatty acids form “soaps” with cations • Na & K soaps – water soluble • Ca & Mg soaps – not water soluble • Poorly digested • Major issue in feeding fats to ruminants

  11. Physical Traits of Fatty Acids • Unsaturated fatty acids oxidize spontaneously in presence of oxygen • Auto-oxidation, peroxidation, rancidity • Free radicals formed • Reduce nutritional value of fats • Antioxidants prevent oxidation • Vitamins C and E, selenium

  12. Triglycerides • Most common structure in dietary lipids • Composed of one glycerol molecule and three fatty acids connected by an ester bond (bond between an alcohol and and organic acid) • Fatty acids may be same or mixed Fatty Acid Fatty Acid Glycerol Fatty Acid

  13. Fatty Acid Structure - H - H = O H - C - ( C )n - C - OH Carboxyl group - H - H Carbon group(s) Methyl group

  14. Fatty Acids • With a few exceptions, natural fatty acids: • Contain an even number of carbon atoms • Arranged in an unbranched line • Have a carboxyl group (-COOH) at one end • Have a methyl group (CH3) at the other end

  15. Fatty Acid Chain Length • Short chain: 2 to 6 C (volatile fatty acids) • Medium chain: 8 – 12 C • Long chain: 14 – 24 C • As chain length increases, melting point increases • Fatty acids synthesized by plants and animals have an even number of carbons • Mostly long chain • 16C to 18C fatty acids are most prevalent

  16. Fatty Acid Saturation • Saturated - no double bonds • Unsaturated – contain double bonds • Monounsaturated – one double bond • Polyunsaturated - >1 double bond • The double bond is a point of unsaturation • As number of double bonds increases, melting point decreases

  17. Saturated Fats • All the chemical bonds between the carbon are single bonds C-C-C- • No double bonds • No space for more H atoms; fully “saturated” • Solid at room temperature • Butter, shortening, lard, coconut oil, palm oil, and fully hydrogenated vegetable oils • Poultry skin, whole milk

  18. Mono-Unsaturated Fatty Acids • Only one double bond • Therefore, two H atoms can be added • Liquid at room temperature • Olive oil, canola oil, peanut oil • Other sources: avocado, almonds, cashews, pecans and sesame seeds (tahini paste)

  19. Poly-Unsaturated Fatty Acids • Two or more double bonds • Include omega-3 and omega-6 fatty acids (essential fatty acids) • Linolenic acid: omega 3 fatty acid • Linoleic acid: omega 6 fatty acid • Richest sources of poly-unsaturated fatty acids include: • Vegetable oils • Corn, sunflower, safflower, cotton seed oils

  20. Saturation • Unsaturated fatty acids • Converted to saturated fatty acids by rumen microbes • More susceptible to rancidity • Oxidation of double bonds produces peroxides and free radicals, which can cause damage to other compounds • Antioxidants • Vitamins E, C • Carotenoids • Such as beta-carotene, lycopene • Selenium

  21. Fatty-acid Nomenclature • Named according to chain length • C18

  22. Fatty-acid Nomenclature • Named according to the number of double bonds • C18:0 Common name: Stearic acid

  23. Fatty-acid Nomenclature • Named according to the number of double bonds • C18:1 Common name: Oleic acid

  24. Fatty-acid Nomenclature • Named according to the number of double bonds • C18:2 Common name: Linoleic acid

  25. Fatty-acid Nomenclature • Named according to the number of double bonds • C18:3 Common name: Linolenic acid

  26. Fatty-acid Nomenclature • Named according to the location of the first double bond from the non-carboxyl end (count from the methyl end) • Omega system (e.g., omega 3, 3) • n–system (e.g., n–3)

  27. Fatty-acid Nomenclature Omega 9 or n–9 fatty acid Omega 6 or n–6 fatty acid Omega 3 or n–3 fatty acid

  28. Fatty Acid Synthesis Issues Ω-3 Ω-6 Ω-9 C-C-C=C-C-C=C-C-C=C-C-C-C-C-C-C-C-COOH • Animals can synthesize a fatty acid with a double bond in the omega 9 position but not at either 3 or 6 positions • Omega-3 and omega-6 fatty acids must be derived from diet • Cold water fish accumulate high levels of omega 3 fatty acids from their diet

  29. Omega System and Essential Fatty Acids • Linoleic acid is an omega-6 fatty acid • Linolenic and arachidonic acids are omega-3 fatty acids • Linoleic and linoleic acids are essential fatty acids • Arachidonic acid can be synthesized from linoleic acid, so not essential • Exception is cats (of course)

  30. Fatty-acid Nomenclature • Named according to location of H’s • Cis or trans fatty acids

  31. H H H H 2 2 2 H C C C C C 3 C C C C H H H H 2 2 2 2 Fatty-acid Nomenclature

  32. Geometrical isomers due to double bond Cis occurs naturally bend in acyl chain Trans Not as common Found in hydrogenated oils Results from bacterial synthesis In fats in ruminants!! Straight acyl chains Chain branching Straight Synthesized by mammals and plants Branched Synthesized by bacteria Isomers

  33. Cis Fatty Acids

  34. Hydrogenation of Fatty Acids • To protect fats from becoming rancid, poly-unsaturated fatty acids may be hydrogenated • Increases saturation and stability - more resistant to oxidation • Unsaturated fats entering rumen are naturally hydrogenated (“bio”-hydrogenated) • Transforms the H-H configuration from cis to trans configuration • Trans configuration alters biological availability • Trans configuration alters biological effects • Suppresses de novo milkfat synthesis in mammary gland

  35. Review of Fatty Acid Nomenclature • Chain length • Most fatty acids have an equal number of carbons • Fish oil is rich in odd-numbered FAs • Double bonds • Number • Location from methyl or carboxyl end • Degree of “saturation”

  36. Melting Points • Affected by chain length • Longer chain = higher melting temp Fatty acid:C12:0 C14:0 C16:0 C18:0 C20:0 Melting point:44°C 58°C 63°C 72°C 77°C Which fatty acids are liquid at room temperature? Which fatty acids are solid at room temperature?

  37. Chain Length • In most fats with a mixture of fatty acids, the chain length of the majority of fatty acids will determine the “hardness” of the fat • <10 carbons = liquid • Between 10 and 20 carbons = ??? • >20 carbons = solid

  38. Melting Points • Affected by number of double bonds • More saturated = higher melting temp Fatty acid:C18:0 C18:1 C18:2 C18:3 Melting point:72°C 16°C –5°C –11°C Which fatty acid is liquid at room temperature? Which fatty acids are solid at room temperature?

  39. Essential Fatty Acids • Must be in diet • Tissues can not synthesize • Linoleic acid (18:2) • Omega-6-FA • Linolenic acid (18:3) • Omega-3-FA • Arachidonic (20:4) • Not found in plants! • Can be synthesized from C18:2 (linoleic acid) in most mammals (except in cat) • Essential nutrient in the diet of cats

  40. Functions of Essential Fatty Acids • A component of the phospholipids in cell membranes • Precursor for prostaglandins: arachidonic acid • Important metabolic regulator • Contraction of smooth muscle • Aggregation of platelets • Inflammation

  41. Arachidonic Acid • Prostaglandins • Thrombocyclin • Prostacyclin • Leukotrenes • Neurotransmitters • Cychrome P450 • Synthesized in liver • elongates linoleic acid (C18:2)

  42. Essential Fatty Acids • Since dietary poly-unsaturated fatty acids are hydrogenated to saturated fatty acids in the rumen by the microbes, how do ruminants meet their essential fatty acid requirement? • By-pass (rumen protected) lipids • Microbial lipid synthesis • Microbes don’t utilize lipids for energy, but they do synthesize them for their cell membranes

  43. Essential Fatty Acids • Deficiency of essential fatty acid intakes: • Growth retardation • Problems with reproduction • Skin lesions • Kidney and liver disorders

  44. Simple Lipids • Neutral fats and oils • Monoacyl glycerols (monoglycerides) • Diacyl glycerols (diglycerides) • Diglycerides found in plant leaves • One fatty acid is replaced by a sugar (galactose) • Triacyl glycerols (triglycerides) • Triglycerides found in seeds and animal adipose tissue • Triacyl glycerols (triglycerides) • Lipid storage form • Where in the body? Adipocytes!! • Most lipids consumed are triglycerides

  45. Triglyceride Structure • Fatty acid composition of triglyceride varies according to function • Membrane lipids must be fluid at all temperatures • Contain more unsaturated fatty acids • Lipids in tissues subjected to cooling (e.g., hibernators or tissues in extremities) • Contain more unsaturated FAs • Butterfat (milk fat) is fairly fluid in spite of containing mostly saturated FAs • Why? Chain length!!

  46. Most Common Fatty Acids in Di- and Triglycerides CH3(CH2)nCOOH

  47. Complex Lipids - Phospholipids • Two primary types: • Glycerophosphatides • Core structure is glycerol • Part of cell membranes, chylomicrons, lipoproteins • Sphingophosphatides • Core structure is sphingosine • Part of sphingomyelin

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