3 carb overview

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3 carb overview

  1. 1. Overview ofCarbohydrate Digestion and Metabolism
  2. 2. FST/AN/HN 761 FST 761 Dr. Jeff Firkins – Carbohydrates Dr. Josh Bomser – Lipids TA- Amy Long, MS Reading / Writing Assignments Text - Biochemical and Physiological Aspects of Human Nutrition- Martha H. Stipanuk. Today – Overview of carbohydrates (Jan 7)
  3. 3. Carbohydrates•Carbohydrates are called carbohydrates because theyare essentially hydrates of carbon (i.e. they arecomposed of carbon and water and have acomposition of (CH2O)n.•The major nutritional role of carbohydrates is toprovide energy and digestible carbohydrates provide4 kilocalories per gram. No single carbohydrate isessential, but carbohydrates do participate in manyrequired functions in the body.
  4. 4. Photosynthesis: Sun’s energy becomes part of glucose molecule energy Carbon dioxide Water GLUCOSE Chlorophyll 6 CO2 + 6 H20 + energy (sun) C6H12O6 + 6 O2
  5. 5. 120 grams of glucose / day = 480 calories
  6. 6. Simple Sugars -
  7. 7. Disaccharides
  8. 8. Complex carbohydrates Oligosaccharides Polysaccharides  Starch  Glycogen  Dietary fiber (Dr. Firkins)
  9. 9. Starch Major storage carbohydrate in higher plants Amylose – long straight glucose chains (a1-4) Amylopectin – branched every 24-30 glc residues (a 1- 6) Provides 80% of dietary calories in humans worldwide
  10. 10. Glycogen Major storage carbohydrate in animals G G G Long straight glucose G GG G G chains (a1-4) G G G Branched every 4-8 glc G G a 1-6 link G residues (a 1-6) a 1-4 link G G G More branched than G G starch Less osmotic pressure Easily mobilized
  11. 11. Digestion Pre-stomach – Salivary amylase : a 1-4 endoglycosidase G G G G G a Limit dextrins G G G G GG G G G G G amylase G G G G G G G a 1-6 link G G maltotriose G a 1-4 link G G G G G G maltose G G isomaltose
  12. 12. Stomach Not much carbohydrate digestion Acid and pepsin to unfold proteins Ruminants have forestomachs with extensive microbial populations to breakdown and anaerobically ferment feed
  13. 13. Small Intestine Pancreatic enzymesa-amylase maltotriose maltose G G G G G G G G + G G a amylase amylose G G G G G G G G G G G G G G G G G amylopectin a Limit dextrins
  14. 14. Oligosaccharide digestion..cont G G G a Limit dextrins G G G G sucrase G G maltase GG Glucoamylase (maltase) or G G G a-dextrinase G G a-dextrinase G G G G G G G G G
  15. 15. Small intestine Portal for transport of virtually all nutrients Water and electrolyte balance Enzymes associated with intestinal surface membranes i. Sucrase ii. a dextrinase iii. Glucoamylase (maltase) iv. Lactase v. peptidases
  16. 16. Carbohydrate absorption Hexose transporterapical basolateral
  17. 17. Glucose and galactose absorption Read Chapter 5 and answer the questions on page 102 of Stipanuk. Be prepared to discuss them on Friday
  18. 18. Carbohydrate malabsorption  Lactose intolerance (hypolactasia), page 100.  Decline lactase with age  Lactose fermented in LI –  Gas and volatile FA  Water retention – diarrhea/bloating  Not all populations  Northern European – low incidenceb 1-4 linkage  Asian/African Americans – High
  19. 19. Metabolism – the chemical changesthat take place in a cell that produceenergy and basic materials needed forimportant life processes-millions of cells-Multiple organs (liver, adipose, heart, brain)-Thousands of enzymes-Various conditions (fed, fasted, exercise, stress)
  20. 20. Carbohydrates Serve as primary source of energy in the cell Central to all metabolic processes GlucoseCytosol - anaerobic Hexokinase Pentose Phosphate Glucose-6-P Glc-1- phosphate Shunt glycolysis glycogen Pyruvate
  21. 21. cytosol Pyruvatemitochondria(aerobic) Aceytl CoA FATTY ACIDS Krebs Reducing cycle equivalents AMINO ACIDS Oxidative Phosphorylation (ATP)
  22. 22. GlucoseNo mitochondria Glucose Glucose Glucose The Full Glycogen Monty Lactate
  23. 23. Fasted State Glucose Need 13.8 kJ/mol ATP = -30 kJ/mol G-6-Pase Hexokinase -16.7 kJ/molPentosePhosphate Glucose-6-P Glc-1- phosphateShunt glycolysis GNG glycogen Pyruvate
  24. 24. Controlling Metabolic Flux1. Control enzyme levels2. Control of enzyme activity (activation or inhibition)
  25. 25. Control of enzyme activityRate limiting step
  26. 26. insulin IR P Protein Kinase B Protein Kinase B (inactive) OH P (active)Glycogen synthase kinase OH (active) P Glycogen(inactive) kinase synthase P OH Glycogen synthase Glycogen synthase (inactive) (active) Glycogen formation
  27. 27. Controlling Metabolic Flux1. Control enzyme levels2. Control of enzyme activity (activation or inhibition)3. Compartamentalization Fatty acid oxidation occurs in mitochondrial matrix Fatty acid synthesis occurs in endoplasmic reticulum membrane exposed to the cytoplasm of the cell.4. Hormonal control
  28. 28. Glucose utilization
  29. 29. Stage 1 – postparandialAll tissues utilize glucoseStage 2 – postabsorptiveKEY – Maintain blood glucoseGlycogenolysisGlucogneogenesisLactatePyruvateGlycerolAAPropionateSpare glucose by metabolizing fatStage 3- Early starvationGluconeogenesisStave 4 – Intermediate starvationgluconeogenesisKetone bodiesStage 5 – Starvation
  30. 30. Carbohydrate Metabolism/ Utilization- Tissue Specificity Muscle – cardiac and skeletal  Oxidize glucose/produce and store glycogen (fed)  Breakdown glycogen (fasted state)  Shift to other fuels in fasting state (fatty acids) Adipose and liver  Glucose  acetyl CoA  Glucose to glycerol for triglyceride synthesis  Liver releases glucose for other tissues Nervous system  Always use glucose except during extreme fasts Reproductive tract/mammary  Glucose required by fetus  Lactose  major milk carbohydrate Red blood cells  No mitochondria  Oxidize glucose to lactate  Lactate returned to liver for Gluconeogenesis

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