10/14/20131LipidsDr. Josie CoverdaleWhat makes lipids unique?• Solubility in non‐polar organic solvents– Ether extract• Hydrophobic nature• Uses/functions beyond a source of dietary energy• Often limited concentrations in herbivore diets– Supplemental10/14/20132Functions and Properties• Concentrated source of energy (9 kcal/g)• Energy reserve• Provide insulation • Supply essential fatty acids• Formation of cell membranes• Biological functions– Sterols, phospholipids, glycolipids• Synthesis of hormones– Steroids, prostaglandins• Transport fat soluble vitamins• Palatability and aromaCommon Physical Properties of Lipids• 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– 2.25 x as much energy10/14/20133Lipids• Location in body– Membranes– Blood and liver (bound to transport proteins)– Adipocytes (adipose tissue)Scanning electron microscope (SEM) image of human adipocyteLipids or Glucose for Energy? More reduced state More potential for oxidationLess reduced state Less potential for oxidationFatty AcidGlucose10/14/20134Physical 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• FA form “soaps” with metals– Na & K soaps –water soluble– Ca & Mg soaps –not water solubleLipid Structure10/14/20135Fatty Acid Structure• Linked by ester bondH - C - ( C )n-C -OH-H-H-H-H= OCarboxyl groupCarbon group(s)*varies in number*Methyl groupFatty Acids• With a few exceptions, natural fatty acids:– Contain an even number of carbon atoms– Arranged in an unbranched line– Carboxyl group (‐COOH) at one end– Methyl group (CH3) at the other end10/14/20136Fatty Acid Chain Length• Short chain: 2 to 6 C• Medium chain: 8 –12 C• Long chain: 14 –24 C• As chain length increases, melting point increases• FA synthesized by plants and animals have even number C– Mostly long chain– 16C to 18C most prevalentFatty Acid Saturation• Saturated ‐ no double bonds• Unsaturated – contain double bonds– Monounsaturated –one double bond– Polyunsaturated ‐ >1 double bond– Double bond is a point of unsaturation• As number of double bonds increases, melting point decreases10/14/20137Fatty Acid Isomers• Geometrical isomers due to double bond– Cis• occurs naturally• bend in acyl chain– Trans• Not as common• Hydrogenated oils• Bacterial synthesis• Straight acyl chains• Chain branching– Straight• Synthesized by mammals and plants– Branched• Synthesized by bacteriaPhysical Traits of Fatty Acids• Unsaturated FA oxidize spontaneously in presence of oxygen– Auto‐oxidation, peroxidation, rancidity– Methelene interrupts double bonds– Free radicals formed• Damage tissue or nutritional value of fats– Antioxidants prevent o xidation10/14/20138Fatty Acid Nomenclature• Named according to chain length and number of double bonds– C18:0• Common name– Stearic acidFatty‐acid nomenclature• C18:1• Common name– Oleic acid10/14/20139Designating Location of Double Bonds• Named according to the location of the lastdouble bond– Omega system (e.g., omega 3, 3)– n– system (e.g., n–3)• Count from the methyl endOmega or n DesignationOmega 9 or n–9 fatty acidOmega 6 or n–6 fatty acidOmega 3 or n–3 fatty acid10/14/201310Omega SystemC‐C‐C=C‐C‐C=C‐C‐C=C‐C‐C‐C‐C‐C‐C‐C‐COOH• Animal can put in 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 = essential• Cold water fish accumulate omega 3 fatty acids from their diet– Health benefits of omega 3 fatty acidsΩ-3Ω-6Ω-9Carbon Numbering SystemsCH3CH2CH2CH2CH2CH2CH2COOHC number 8 7 6 5 4 3 2 1n or ω 1 2 3 4 5 6 7 8Letter ω ω‐1 ‐ δ γ β αω end Carboxyl end10/14/201311Designating Position of BondsCH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH• Numeric (9,12 – 18:2)• ∆ (18:2 ∆ 9,12)• n (18:2 n‐6)• ω (18:2 ω‐6)Essential Fatty Acids• Must be in diet– Tissue can not synthesize from precursors– Linoleic acid (18:2)– Linolenic acid (18:3)– Arachidonic (20:4)• Can be synthesized from C18:2• Essential in the cat10/14/201312Functions of EFA• Components of phospholipids in cell membranes• Precursor for prostaglandins: arachidonic acid• Metabolic regulator• Deficiency symptoms– Growth retardation, reproductive problems, skin lesions, and kidney and liver disordersTriglycerides• Fatty acid structure c ommon in dietary lipids• Composed of glycerol and 3 fatty acids connected by an ester bond– Fatty acids may be same or mixedGlycerolFatty AcidFatty AcidsFatty Acid10/14/201313Lipid DigestionMonogastric Digestion• Challenges– Triglycerides (TG) are too large for absorption– Lipids are not water soluble•