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Lecture 5: Lipids and Carbohydrates Craig Kasper Fish Nutrition Part 1: Lipid Characteristics Lipid = a compound that is insoluble in water, but soluble in an organic solvent (e.g., ether, benzene, acetone, chloroform) “lipid” is synonymous with “fat”, but also includes phospholipids, sterols, etc. chemical structure: glycerol + fatty acids Lipid Molecule Nutritional Uses of Lipids We already know that lipids are concentrated sources of energy (9.45 kcal/g) other functions: 1) provide means whereby fat-soluble nutrients (e.g., sterols, vitamins) can be absorbed by the body 2) structural element of cell, subcellular components 3) components of hormones and precursors for prostaglandin synthesis Lipid Classes 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 vs. Unsaturated Fatty Acids saturated: the SFA’s of a lipid have no double bonds between carbons in chain polyunsaturated: more than one double bond in the chain most common polyunsaturated fats contain the polyunsaturated fatty acids (PUFAs) oleic, linoleic and linolenic acid unsaturated fats have lower melting points stearic (SFA) melts at 70oC, oleic (PUFA) at 26oC Fatty Acids Commonly Found in Lipids Sat. Fatty Acids Butyric Palmitic Stearic Unsat. Fatty Acids Oleic Linoleic Linolenic Formula C4H8O2 C16H22O2 C18H36O2 Formula C18H34O2 C18H32O2 C18H30O2 Melting Point (oC) Liquid 63 70 Melting Point (oC) Liquid Liquid Liquid Saturated vs. Unsaturated Fats saturated fats tightly packed, clog arteries as atherosclerosis because of double bonds, polyunsaturated fats do not pack well -- like building a wall with bricks (sat.) vs. irregular-shaped objects (unsat.) plant fats are much higher in PUFA’s than animal fats Saturated vs. Unsaturated FA’s Plant vs. Animal Fat corn Sat. FA’s Myristic Palmitic Stearic Unsat. FA’s Oleic Linoleic Linolenic Arachid. soy tallow lard 7.0 2.4 8.5 3.5 3 27 21 32.2 7.8 45.6 45.0 17 54.4 7.1 40 2 0.5 48 11 0.6 Lipid Digestion/Absorption Fats serve a structural function in cells, as sources of energy, and insulation the poor water solubility of lipids presents a problem for digestion: substrates are not easily accessible to digestive enzymes even if hydrolyzed, the products tend to aggregate to larger complexes that make poor contact with the cell surface and aren’t easily absorbed to overcome these problems, changes in the physical state of lipids are connected to chemical changes during digestion and absorption Lipid Digestion/Absorption Five different phases: hydrolysis of triglycerides (TG) to free fatty acids (FFA) and monoacylglycerols solubilization of FFA and monoacylglycerols by detergents (bile acids) and transportation from the intestinal lumen toward the cell surface uptake of FFA and monoacylglycerols into the cell and resynthesis to triglyceride packaging of TG’s into chylomicrons exocytosis of chylomicrons into lymph Enzymes Involved in Digestion of Lipids lingual lipase: provides a stable interface with aqueous environment of stomach pancreatic lipase: major enzyme affecting triglyceride hydrolysis colipase: protein anchoring lipase to the lipid lipid esterase: secreted by pancreas, acts on cholestrol esters, activated by bile phospholipases: cleave phospholipids, activated by trypsin What about Bile??? These are biological detergents synthesized by the liver and secreted into the intestine they form the spherical structures (micelles) assisting in absorption hydrophobic portion (tails of FA) are located to the inside of the micelle, with heads (hydrophillic portion) to the outside they move lipids from the intestinal lumen to the cell surface absorption is by diffusion (complete for FA and monoglycerides, less for others) Factors Affecting Absorption of Lipids amount of fat consumed (fat=digestion=absorption) age of subject ( age = digestion) emulsifying agents ( digestion = absorption) chain length of FA’s (> 18C = digestibility) degree of saturation of FA ( sat = digestibility) overheating and autooxidation (rancidification (rot) at double bond) optimal dietary calcium = optimal FA absorption (high Ca = absorption) Lipid Metabolism/Absorption short chain FA’s are absorbed and enter the portal vein to the liver those FA’s with more than 10 carbons are resynthesized by the liver to triglycerides they are then converted into chylomicrons and pass to the lymphatic system some FA’s entering the liver are oxidized for energy, others stored blood lipids: 45% P-lipids, 35% triglycerides, 15% cholestrol esters, 5% free FA’s Lipid Digestion/ Absorption Lipid Digestion/ Absorption Characteristics of Fat Storage Most of the body’s energy stores are triglycerides storage is in adipose, source is dietary or anabolism (synthesis) from COH or AA carbon skeletons remember obesity? adipose can remove FA’s from the blood and enzymes can put them back Fatty Acid Nomenclature Nomenclature reflects location of double bonds also used are common names (e.g., oleic, stearic, palmitic) linoleic is also known as 18:2 n-6 this means the FA is 18 carbons in length, has 2 double bonds, the first of which is on the 6th carbon arachidonic = 20:4 n-6 What’s in a Name?? Fatty Acid Nomenclature Essential Fatty Acids Only recently determined as essential (1930) body can synthesize cholesterol, phospholipids research: same as AA’s but via addition (EFA’s added improved growth, NEFA’s didn’t) requirement determined by depleting fat reserves of subject animal: difficult Essential Fatty Acids (fish) Most NEAA found in marine food webs Essential fatty acids (to date): – linoleic (18:2 n-6; terrestrials; fish - not really) – linolenic (18:3 n-3; terrestrials; fish) – arachidonic (20:4 n-6; marine maybe) – eicosopentaenoic acid (20:5 n-3, marine) – docosohexaenoic (22:6 n-3, marine) Why? Because elongation beyond 18 carbons is very difficult in marine fish (lack pathways) actual EFA requirement is a matter of whether the fish is FW/SW or WW/CW Essential Fatty Acids (most animals) salmonids need n-3 FA’s for membrane flexibility in cold water (why does this work?) trout can elongate and desaturate n-3 FA’s Linoleic acid (18:2 n-6) is the most essential addition of arachidonic is also helpful in deficient diets, but can be synthesized from linoleic (maybe sparing effect) EFA’s, like EAA’s, must be dietary Essential Fatty Acids LINOLEIC CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH 18:2 n-6 LINOLENIC CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH 18:3 n-3 EICOSOPENTAENOIC ACID CH3CH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)3COOH 20:5 n-3 DOCOSOHEXAENOIC ACID - YOU CAN DO THIS ONE! Lipids as Crustacean Energy Sources Largely, n-6 FA’s (linoleic) used for energy as temperature drops, requirement for monounsaturated and PUFA’s increases change in temperature = change in diet cold water species = increased dietary HUFA’s maturation animals: increased requirement for 20:4 n-6, 20:5 n-3 and 22:6 n-3 for proper spawning Part 2: Carbohydrate Characteristics From: Lovell; D’Abramo et al. General Comments Carbohydrates often written as “COH” much of what we need to know about them, besides their structure, was covered in “Bioenergetics, Parts 1&2” here, we cover structure Carbohydrate Structure Basic chemical structure consists of sugar units found as aldehydes or ketones derived from polyhydric alcohols contain: C, H, O often shown as aliphatic or linear structures, but exist in nature as ringed structures Glucose Structure O CH2OH C-H H- C-OH O H OH HO-C-H H OH HO H-C-OH H OH H-C-OH Haworth perspective CH2OH H Carbohydrate Classification Usually by the number of sugar units in the molecule: – monosaccharides (glucose) – disaccharides (2 units) maltose (2 glucose units) sucrose (glucose + fructose) – polysaccharides (long chain polymers of monosaccharides – most important polysaccharides to animals are starch and cellulose Starch and Cellulose CH2OH O H O CH2OH OH H H OH H O H O OH H H OH CH2OH O starch CH2OH H O H H O O O OH H OH H H OH O H H H OH cellulose Starch and Cellulose Starch contains -D-glucose linkage Cellulose has a -D-glucose linkage we store starch in muscle tissues as glycogen, peeled off by enzymes when needed cellulose is primary component of plant tissue, largely indigestible to monogastrics must have enzyme, “cellulase”