Lipid Structure and Function

Transcription

1 Lipid Structure and Function

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

3 Lipids or Glucose for Energy? O O O O O O O 2 O ATP Energy-ontaining Nutrients ( and ) Electron Transport hain + 2 O O 2 O 2

4 Lipids or Glucose for Energy? O O O O O O O 2 O More reduced state (more bound to ) More potential for oxidation Less reduced state (more O bound to ) Less potential for oxidation

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

6 Functions and Properties oncentrated 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 ormone-like compounds that modulates many body processes Immune system, nervous systems, and GI secretions Regulatory functions: lower BP, blood clotting, uterine contractions elp 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 (K)

9 Physical Traits of Fatty Acids Form membranes, micelles, liposomes Orient at water:oil interface ontain 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 a & 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 and E, selenium

12 - - = O Fatty Acid Structure - - ( ) n - - O Methyl group - - arbon group(s) arboxyl group

13 Fatty Acids With a few exceptions, natural fatty acids: ontain an even number of carbon atoms Arranged in an unbranched line ave a carboxyl group (-OO) at one end ave a methyl group ( 3 ) at the other end

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15 Fatty Acid hain Length Short chain: 2 to 6 (volatile fatty acids) Medium chain: 8 12 Long chain: As chain length increases, melting point increases Fatty acids synthesized by plants and animals have an even number of carbons Mostly long chain 16 to 18 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 --- No double bonds No space for more 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 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 orn, sunflower, safflower, cotton seed oils

20 Saturation Unsaturated fatty acids onverted 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, arotenoids Such as beta-carotene, lycopene Selenium

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

22 Review of Fatty Acid Nomenclature hain 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 O O

23 Fatty-acid Nomenclature Named according to chain length O O

24 Fatty-acid Nomenclature Named according to the number of double bonds 18: O O ommon name: Stearic acid

25 Fatty-acid Nomenclature Named according to the number of double bonds 18: O O ommon name: Oleic acid

26 Fatty-acid Nomenclature Named according to the number of double bonds 18: O O ommon name: Linoleic acid

27 Fatty-acid Nomenclature Named according to the number of double bonds 18: O O ommon name: Linolenic acid

28 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) O O

29 Fatty-acid Nomenclature Omega 9 or n 9 fatty acid Omega 6 or n 6 fatty acid 2 O O O O Omega 3 or n 3 fatty acid O O

30 Fatty Acid Synthesis Issues Ω-3 Ω-6 Ω-9 --=--=--= OO 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 old water fish accumulate high levels of omega 3 fatty acids from their diet

31 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)

32 Fatty-acid Nomenclature Named according to location of s is or trans fatty acids is-9-octadecenoic acid (Oleic acid) Trans-9-octadecenoic acid (Elaidic acid)

33 Fatty-acid Nomenclature O O O O

34 Isomers Geometrical isomers due to double bond is 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 hain branching Straight Synthesized by mammals and plants Branched Synthesized by bacteria

35 is Fatty Acids

36 Melting Points Affected by chain length Longer chain = higher melting temp Fatty acid: 12:0 14:0 16:0 18:0 20:0 Melting point: Which fatty acids are liquid at room temperature? Which fatty acids are solid at room temperature?

37 hain 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 Acetic Acid (2 ) Vinegar Liquid Stearic Acid (18 ) Beef Tallow Solid Arachidic Acid (20 ) Butter Solid

38 Melting Points Affected by number of double bonds More saturated = higher melting temp Fatty acid: 18:0 18:1 18:2 18:3 Melting point: Which fatty acid is liquid at room temperature? Which fatty acids are solid at room temperature?

39 Acids arbons Double bonds Abbreviation Source Acetic 2 0 2:0 bacterial metabolism Propionic 3 0 3:0 bacterial metabolism Butyric 4 0 4:0 butterfat aproic 6 0 6:0 butterfat aprylic 8 0 8:0 coconut oil apric :0 coconut oil Lauric :0 coconut oil Myristic :0 palm kernel oil Palmitic :0 palm oil Palmitoleic :1 animal fats Stearic :0 animal fats Oleic :1 olive oil Linoleic :2 grape seed oil Linolenic :3 flaxseed (linseed) oil Arachidonic :4 peanut oil, fish oil

40 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! an be synthesized from 18:2 (linoleic acid) in most mammals (except in cat) Essential nutrient in the diet of cats

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

42 Arachidonic Acid Prostaglandins Thrombocyclin Prostacyclin Leukotrenes Neurotransmitters ychrome P450 Synthesized in liver elongates linoleic acid (18:2)

43 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

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

45 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

46 Triglycerides Most common structure in dietary lipids omposed 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 Glycerol Fatty Acid Fatty Acid

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

48 Most ommon Fatty Acids in Diand Triglycerides Fatty acid arbon:double bonds Double bonds Myristic 14:0 Palmitic 16:0 Palmitoleic 16:1 is-9 Stearic 18:0 Oleic 18:1 is-9 Linoleic 18:2 is-9,12 Linolenic 18:3 is-9,12,15 Arachidonic 20:4 is-5,8,11,14 Eicosapentaenoic 20:5 is-5,8,11,14,17 Docosahexaenoic 22:6 is-4,7,10,13,16,19 3 ( 2 ) n OO

49 omplex Lipids - Phospholipids Two primary types: Glycerophosphatides ore structure is glycerol Part of cell membranes, chylomicrons, lipoproteins Sphingophosphatides ore structure is sphingosine Part of sphingomyelin

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51 omplex Lipids - Phospholipids Glycerophosphatides resemble triglyceride in structure except one of the fatty acids is replaced by a compound containing a phosphate group, or occasionally, nitrogen Most prevalent is lecithin

52 Phospholipids Significant use in feed industry as emulsifiers Lipids form emulsion in water Phospholipid sources: Liver, egg yolk, Soybeans, wheat germ Peanuts

53 omplex Lipids - Glycolipids arbohydrate component in structure erebrosides & gangliosides Medullary sheaths of nerves; white matter of brain

54 Derived Lipids Prostaglandins Synthesized from arachidonic acid Several metabolic functions Steroids holesterol, ergosterol, bile acids Terpenes Made by plants arotenoids, xanthophylls

55 Sterols ompounds with multi-ring structure Insoluble in water Present both in plant and animal foods Major sterol is cholesterol owever, cholesterol is found only in animal products (manufactured in liver) igh content in organ meats and egg yolk

56 ommon Sterol ompounds holesterol (a sterol) Vitamin D3 (cholecalciferol) Testosterone (a steroid hormone) Stigmasterol (a phytosterol)