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Volatile Fatty Acids

Biochemistry for beginners-Wk 9

Ruminant Digestion? -cellulose, hemicellulose, starch, water soluble carbohydrates like fructans -complex are broken down into simple sugars by microbes
What are the 3 fibrous carbohydrates? -cellulose -hemicellulose -starch
Cellulose? -glucose units -beta 1-4 linkages which make it straight and more rigid to allow H bonding -more H bonding causes poor flexibility, increased tensile strength and lower solubility in water and dilute acid
Hemicellulose? -heterogeneous (mixture) -core xylose -beta linkages -2 branch points: arabinose, uronic acid -more branch points increases its digestibility and solubility as they can be broken off -often binds to other proteins and carbsto make them not utilizable
Starch? -storage of polysaccharides in plants -amylose and amylopectin -amylose: glucose and alpha 1-4 linkages -amylopectin: glucose and alpha 1-4 linkages and alpha 1-6 branch points -arranged in granules held by H bonds which can be destroyed by heating
stage 1 digestion of cellulose? -cellulose becomes cellobiose by endo beta 1-4 glucanase, then cellobiose becomes glucose from the action of exo beta 1-4 glucanase and beta glucosidases (cellobiase)
Stage 1 digestion of hemicellulose? -hemicellulose becomes lignin hemicellulose complex and then monosachharides -enzymes: endoxylanase, xylosidase, arabinofuranosidase, glucuronidase
Stage 1 digestion of starch? -amylose and amylopectin broken down to oligosaccharides by alpha amylase, then to glucose by maltases -sucrose: glucose + fructose by sucrase -lactose: glucose + galactose by lactase
microbes in starch digestion? -protozoa help stabilize fermentation -bacteria help store polysaccharides
stage 2 of carbohydrate digestion? -glucose goes through glycolysis to become 2 pyruvate (ADP + NAD become 2ATP, 2NADH + H) -pyruvate becomes VFA + CO2 + CH4 + energy
Gas production? -in cows 30L/hr -40% CO2 -30-40% CH4 -5% H -lost by eructation (burbing)
Main VFA produced in carbohydrate digestion? -acetic acid x 2 -butyric acid x 1 -propionic acid x2 -others but very small -VFA is a carbon chain with 6 or less carbons
VFA Production and concentration? -production peaks 4hrs after eating -production is not related to concentration -concentration: depends on diet, mature has more acetic acid and more concentrated has more propionate
Factors affecting VFA production? -diet forage: concentrate ration (less acetic more propionate) -diet buffers (more acetate & CH4) -decreased physical form of diet (e.g. grinding) increases propionate -ionophores (increase propionate) -unsaturated fatty acids (increase propionate)
Energy values in VFA's and glucose in order from lowest to highest -acetic -propionic -butyric -glucose
VFA absorption? -70% in rumen-reticulum by passive transport -10-20% in osmasum butyric > propionate > acetate (rate of absorption) -increases with increased pH due to un-dissociated acids
VFA absorption is greater in grain fed animals, why? -faster fermentation -lower pH -growth of papillae
VFA pathway in the body? -goes to the GIT butyrate become beta hydroxybutyric acid 5% propionate becomes lactic acid -then goes to liver and then body tissues
Propionate pathway? -goes into the rumen wall and to the liver where it is converted to glucose
Propionate chemical pathway? -becomes succinyl-CoA and goes into the CAC where malate is released into the cytosol -malate becomes phosphoenolpyruvate which can either become glucose or pyruvate (more efficient and goes into CAC) to produce energy
Acetic acid chemical pathway? -major product -combines with Co-A to form acetyl-CoA which can then go into the CAC and be used to produce energy -net ATP = 10, as uses 2 ATP
Butyric Acid chemical pathway? -becomes D-3-hydroxybutyrate -this then becomes aceto-acetate and then acetoacetyl coA by either a succinyl coa pathway or coa pathway -with the addition of CoA becomes acetyl Coa and goes into the CAC -net ATP 25 (COA path) and 27 (succinyl path)
effect of VFA's on endocrine system? -propionic-increases blood glucose and causes the release of insulin -butyric-releases insulin and glucagon to increase blood glucose -acetic-nothing -glucose-release of insulin
Microbes and fermentation? -convert plant components to sugars -produces energy and H ions from converting NAD to NADH,H -H ions must be produced otherwise fermentation slows down -however if H ions accumulate this can inhibit fermentation -H ions removed by methanogenesis
CH4 produced by microbes -contributes to 53% total methane emission -14% of the world green house gases
Anaerobic Digestion? -hydrolysis (complex to simple sugars) -fermentation (simple broken to pyruvate) -acetogenesis (pyruvate to VFA) -fermentation (CH4)
Methane inhibitors? -nitrates, sulfates, alkaloids (but they also reduce propionic acid and butyrate) -chloral hydrate -myristic acid
Reductive Acetogenesis? -uses H to form acetate which can be used as energy, favourable to methanogenesis
Methanogenesis vs. acetogenesis pathway? 4H2 + HCO3- + H+ to form CH4 + 3 H20 -136 4H2 + 2HCO3- + H+ to form acetate- + 4H20 -105
pyruvate to acetate? -pyruvate to acetyl-phosphate to acetate
pyruvate to butyrate? -pyruvate to acetyl coA to acetoacetyl-coa, to beta hydroxybutyryl-coa to crotonyl-coa to butyryl-coa to butyrate
pyruvate to propionate? -pyruvate to lactate, to lactyl-coA to acrylyl-coa to propionyl-coa to propionate
Created by: sherloki



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