碳水化合物-单页 (1)

动物营养研究所Animal Nutrition Institute, Sichuan Agricultural UniversityFor graduate studentsAnimal NutritionTheory and Technology YU, Jie(虞 洁)Ph.D., Associate ProfessorCarbohydrates Types and Structure  Absorption, transport, distribution  Metabolism (physiology)  CHO application动物营养研究所CarbohydratesTypes and Structure动物营养研究所Carbohydrates (CHO) Made from carbon, oxygen, and hydrogen- Polyhydroxy aldehydes (aldoses) - Ketones (ketoses) - Derivatives of aldoses and ketoses CHO interact well with water- The O-H bond is a polar bond - Multiple hydroxyl groups Free or associated with other macronutrients- Proteins (glycoproteins), Lipids (glycolipids) Described by their functional group and based on the number of C atoms- Aldopentose (5-carbon aldose), Ketohexose (6-carbon ketose)动物营养研究所Aldoses动物营养研究所动物营养研究所Kinds of CHO动物营养研究所Starch动物营养研究所Categories动物营养研究所CarbohydratesAbsorption, Transport and Distribution动物营养研究所Absorption of HexosesAbsorption of HexosesAbsorption of HexosesMonosaccharide TransportPortal circulation carries them to the liverThe liver is the major site of galactose and fructose metabolism (~100%)-Taken up by specific receptors –facilitated transport-Converted to glucose derivatives, enter the glycolytic pathwayBlood levels of galactose and fructose are not strictly controlled by hormonal regulation as is glucoseGlucose is nutritionally the most important monosaccharideGlucose Transport and Cellular UptakeExtensively metabolized in liver (30-35%) -Remainder passes into systemic blood supply and enters into muscle, kidney, and adipose tissueCellular Uptake-Requires facilitated transport-Insulin dependent in skeletal muscle and adipose tissue-Most cells are dependent on a continuous supply for ATP generation Concentration in blood must be precisely controlledBlood GlucoseGlucose circulates in human blood at a range of 5-7 mM between mealsGlucose is available to all cells that need it, especially brain and RBCsThe liver is responsible for releasing glucose between meals to maintain euglycemia-Glucose is derived fromLiver glycogen breakdownGluconeogenesisBlood GlucoseBlood Glucose HomeostasisFor the post-absorptive stateGlucose Cellular UptakeGlucose entry into cells is down a concentration gradient from blood to extracellular fluid to cell cytoplasm-Exception: enterocytes and renal tubules where it is moved against the gradient in a symport with Na+which is moved down its gradientSkeletal muscle presents a problem since it can be 40-50% of body weight for lean, active people and could take up a lot of glucose.-Requires regulation of glucose uptake by regulating the number of available transportersGlucose Cellular UptakeGLUT SpecificityGLUT4 TransporterIn the resting, post-absorptive state, ~3-10% of GLUT4 transporters in adipose and muscle cells are located in the cell membranesRemainder are in intracellular vesiclesTwo well established mechanisms for increasing GLUT4 content at the cellular membrane-Adipose tissue: insulin-Skeletal muscle: insulin, increased muscle contractionGLUT4 TransporterInsulin sets in motion a mechanism that increases the release of GLUT4 transporters from their intracellular storage sites and inserting them into cell membranesThis results in more transporters and a faster rate of glucose uptaketransporttransportCarbohydrates Metabolism (physiology)Monosaccharide MetabolismDepends on energy demands at the timeRegulatory hormones-Insulin, glucagon, epinephrine, cortisol-Covalent modification of enzymesCellular concentrations of metabolites, ions and ATP -Allosteric modification of enzymesMonosaccharide MetabolismGlycogenesisProcess by which glucose is stored as glycogen Liver-7% of wet weight is glycogen-Important for blood glucose homeostasisSkeletal muscle-1% of wet weight-75% of body’s storage due to contribution of body mass-Energy source for that muscle fiber onlyGlycogen Granules(Glycosome)Found in cell cytosol of liver and skeletal muscle Contains:-The glycogen molecule with glycogenin-Glycogen synthase-Glycogen phosphorylase-Branching enzyme-Debranching enzyme-KinasesRegulate synthesis and breakdown -PhosphataseGlycogeninThe protein that starts off the glycogen molecule Found at the very core of the particleGlycogenin has self glycosylating activity -Able to add about 7 glucose units onto itself, end to end-Glycogen synthase takes over adding more and branching enzyme creates the branchesGlycogen MoleculeGlycogen synthase-Creates long chains of glucose joinedby α1-4 bondsBranching enzymes createsthe branches-Branches formed using α1-6glycosidic bonds located roughly every 13glucosyl units-Creates a compact structure-Creates multiple non-reducing ends toprovide a large source of available energyGlycogenGlycogenesisSteps in GlycogenesisGlycogenolysisSteps in GlycogenolysisMonosaccharide MetabolismAnaerobic Glycolysis-Catabolism of glucose to lactate-Fructose and Galactose are primarily metabolized in the liverStages of GlycolysisGlucose PhosphorylationPriming/Splitting Stages ofGlycolysisRedox StageWhen Would Glycolysis tobe Active?Liver-When the diet is consistently high in CHO-Following a CHO-rich mealSkeletal muscle-When blood glucose is high following a CHO-rich meal-When muscle is active and---There are large stores of glycogen---or small stores of glycogen, but the intensity of activity is highPoints of GlycolysisRegulationLiver-At the glucokinase step ---How?-At the PFK1 step (the master valve)Skeletal muscle-At the glycogen breakdown step-At the hexokinase step ---How?-At the PFK1 step (the master valve)Lactate FormationAny time glycolysis occurs, generating pyruvate, lactate can be produced because:-Lactate Dehydrogenase (LDH) has a fairly high activity in muscle Lactate increases when-Exercise work load increases-Muscle glycogen is relatively high-FT fibers are being used-Blood flow is reduced or blood oxygen content is low-Oxidative capacity is low (e.g. cyclist doing arm cranking)Lactate Formation and GlycogenLDH ReactionLactate/Pyruvate Membrane TransportBoth lactate and pyruvate can cross the plasma (cell) membrane, accompanied by a protonSpecific transporters called monocarboxylate transporters (MCT)Net direction depends on concentration gradientAlso transports pyruvate into mito matrixSeveral different kinds: MCT1 (ST fibers) and MCT4 (FT fibers)Intercellular Lactate Shuttle。