Lipid (Part 1 & II) - PDF

LIPID (PART I & II) IMK227 Dr. Lee Lai Kuan  LIPID  Synonymous with “fat”  Insoluble in water, soluble in organic solvents  Includes fats and oils – mostly triglycerides ◦ Fat: solid at room temperature ◦ Oil: liquid at room temperature  Chemical structure: gl...

LIPID (PART I & II) IMK227 Dr. Lee Lai Kuan  LIPID  Synonymous with “fat”  Insoluble in water, soluble in organic solvents  Includes fats and oils – mostly triglycerides ◦ Fat: solid at room temperature ◦ Oil: liquid at room temperature  Chemical structure: glycerol + fatty acids Fatty Acid 1 Fatty Acid 2 Glycerol Fatty Acid 3  Classification  Simple: FA’s esterified with glycerol  Compound: Same as simple, but with other compounds also attached  Phospholipids: Fats containing phosphoric acid and nitrogen (lecithin)  Glycolipids: FA’s compounded with CHO, but no N  Derived lipids: Substances from the above derived by hydrolysis  Sterols: Large molecular wt. alcohols found in nature and combined w/FA’s (e.g., cholesterol)  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  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  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  Fatty Acids Carbon groups Carboxyl group Methyl group  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 Acids Carbons Double bonds Abbreviation Source Acetic 2 0 2:0 bacterial metabolism Propionic 3 0 3:0 bacterial metabolism Butyric 4 0 4:0 butterfat Caproic 6 0 6:0 butterfat Caprylic 8 0 8:0 coconut oil Capric 10 0 10:0 coconut oil Lauric 12 0 12:0 coconut oil Myristic 14 0 14:0 palm kernel oil Palmitic 16 0 16:0 palm oil Palmitoleic 16 1 16:1 animal fats Stearic 18 0 18:0 animal fats Oleic 18 1 18:1 olive oil Linoleic 18 2 18:2 grape seed oil Linolenic 18 3 18:3 flaxseed (linseed) oil Arachidonic 20 4 20:4 peanut oil, fish oil  Essential fatty acids  Required for important functions in the body  Must be provided by the diet because our bodies cannot make them  Essential fatty acids linoleic (18:2 n-6) linolenic (18:3 n-3) arachidonic (20:4 n-6) eicosopentaenoic acid (20:5 n-3) docosohexaenoic (22:6 n-3) 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  Arachidonic Acid  Prostaglandins ◦ Thrombocyclin ◦ Prostacyclin ◦ Leukotrenes ◦ Neurotransmitters ◦ Cychrome P450  Synthesized in liver ◦ elongates linoleic acid (C18:2)  Triglyceride / Triacylglycerol O R COOH HO CH2 HO C O CH2 O cataylst R COOH CH HO C O CH + HO O R COOH HO CH2 HO C O CH2 triacylglycerol Fatty acid glycerol 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  Phospholipids  Significant use in feed industry as emulsifiers ◦ Lipids form emulsion in water  Phospholipid sources: ◦ Liver, egg yolk, ◦ Soybeans, wheat germ ◦ Peanuts Complex Lipids - Glycolipids  Carbohydrate component in structure  Cerebrosides & gangliosides ◦ Medullary sheaths of nerves; white matter of brain  Derived Lipids  Prostaglandins ◦ Synthesized from arachidonic acid  Several metabolic functions  Steroids ◦ Cholesterol, ergosterol, bile acids  Terpenes ◦ Made by plants  Carotenoids, xanthophylls  Sterols  Compounds with multi-ring structure  Insoluble in water  Present both in plant and animal foods  Major sterol is cholesterol ◦ However, cholesterol is found only in animal products (manufactured in liver)  High content in organ meats and egg yolk Functions and Properties  Concentrated source of energy (9 kcal/g)  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 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)  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)  Lipid Metabolism Hydrolysis Hydrogenation De Novo synthesis β-oxidation Ketogenesis Triacylglycerol Hydrolysis  Split by water and acid or enzyme catalyst  Produce glycerol and 3 fatty acids O CH2 O C (CH2)14CH3 O H+ CH O C (CH2)14CH3 +3 H2O O CH2 O C (CH2)14CH3 CH2 OH O CH OH + 3 HO C (CH2)14CH3 CH2 OH Triacylglycerol hydrogenation  Unsaturated compounds react with H2  Ni or Pt as catalyst  C=C bonds C–C bonds  Hydrogenation O CH2 O C (CH2)5CH CH(CH2)7CH3 O Ni CH O C (CH2)5CH CH(CH2)7CH3 + 3 H2 O CH2 O C (CH2)5CH CH(CH2)7CH3 O CH2 O C (CH 2)14CH 3 O CH O C (CH 2)14CH3 O CH 2 O C (CH 2)14CH 3  De Novo Synthesis of Fatty Acids  Occur in cytoplasm  Production of Acetyl CoA  Carboxylation of Acetyl CoA  Fatty acid synthase: a multienzyme complex ◦ AcetylCoA-ACP transacylase ◦ MalonylCoA-ACP transacylase ◦ ß-ketoacyl-ACO synthase ◦ Palmitoyl thioesterase De Novo Synthesis of Fatty Acids Production of (a)  Translocation of mitochondrial citrate to Acetyl CoA and cytosol NADPH  Conversion of citrate to acetyl CoA + oxaloacetate by citrate lyase  Requirement: ATP and Citrate Translocation of mitochondrial citrate to cytosol Conversion of citrate to acetyl CoA + oxaloacetate by citrate lyase De Novo Synthesis of Fatty Acids (b) Carboxylation of  Carboxylation of AcetylCoA acetyl CoA to to malonylCoA by AcetylCoA carboxylase malonyl CoA  Coenzyme: Biotin  De Novo Synthesis of Fatty Acids (c) Fatty acid synthase: a multienzyme complex ◦ Substrate: AcetylCoA  Carbons 15 and 16 of palmitic and MalonylCoA acid from priming acetyl CoA ◦ End Product: Palmitic  Carbons 1-14 of palmitic acid acid are derived from 7 malonyl ◦ Site: Cytosol CoA ( 2 carbons from malonyl ◦ Priming Molecule: Acetyl CoA are added 7 times to the CoA priming acetylCoA molecule ◦ Primary enzyme of  NADPH + H+ are from HMP- synthesis: Fatty acid Shunt synthase 1 AcetylCoA + 7 malonylCoA + 14 NADPH+ 14 H Palmitic acid + 7 CO2 + 6H2O+ Co-A-SH +14 NADP  β-Oxidation of fatty acids  The break down of a fatty acid to acetyl- CoA  ‘glycolysis’ of fatty acids  Occurs in the mitochondria  Aerobic Beta Oxidation Beta Oxidation Beta Oxidation Beta Oxidation Beta Oxidation CHOLESTEROL SYNTHESIS AND EXCRETION Occurs as free (brain) and esterified (adrenal cortex)form. Plasma membrane & lipoproteins. Normal healthy adults synthesize -- approximately 1g/day. consume approximately 0.3g/day. 150 - 200 mg/dL is maintained in serum by controlling the level of de novo synthesis. Cholesterol is utilized in the formation of ~membranes ~synthesis of the steroid hormones ~bile acids ( greatest proportion)  CHOLESTEROL BIOSYNTHESIS ER bound,req. NADPH Synthesis of mevalonate cytoplasm Formation of isoprenoid unit 6 isoprenoid unit form squalene NADPH Formation of lanosterol Formation of cholesterol