1 / 26

Overview of Carbohydrate Digestion and Metabolism

Overview of Carbohydrate Digestion and Metabolism. Carbohydrates. Carbohydrates are composed of carbon and water and have a composition of (CH 2 O) n. The major nutritional role of carbohydrates is to provide energy and digestible carbohydrates provide 4 kilocalories per gram. energy.

saman
Download Presentation

Overview of Carbohydrate Digestion and Metabolism

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Overview of Carbohydrate Digestion and Metabolism

  2. Carbohydrates • Carbohydrates are composed of carbon and water and have a composition of (CH2O)n. • The major nutritional role of carbohydrates is to provide energy and digestible carbohydrates provide 4 kilocalories per gram. energy Carbon dioxide Water Chlorophyll GLUCOSE 6 CO2 + 6 H20 + energy (sun) C6H12O6 + 6 O2

  3. Simple Sugars -

  4. Disaccharides

  5. Complex carbohydrates • Oligosaccharides • Polysaccharides • Starch • Glycogen • Dietary fiber (Dr. Firkins)

  6. Starch • Major storage carbohydrate in higher plants • Amylose – long straight glucose chains (α1-4) • Amylopectin – branched every 24-30 glc residues (α 1-6) • Provides 80% of dietary calories in humans worldwide

  7. Glycogen • Major storage carbohydrate in animals • Long straight glucose chains (α 1-4) • Branched every 4-8 glcresidues (α1-6) • More branched than starch • Less osmotic pressure • Easily mobilized G G G G G G G G G G G a 1-6 link G G G G a 1-4 link G G G G

  8. Digestion • Pre-stomach – Salivary amylase : a 1-4 endoglycosidase G G G a Limit dextrins G G G G G G G G G G G G amylase G G G G G a 1-6 link G G G G maltotriose G G a 1-4 link G G G G G G maltose G G isomaltose

  9. Stomach • Not much carbohydrate digestion • Acid and pepsin to unfold proteins • Ruminants have forestomachs with extensive microbial populations to breakdown and anaerobically ferment feed

  10. Small Intestine • Pancreatic enzymes a-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

  11. Oligosaccharide digestion..cont a Limit dextrins G G G G sucrase G G G G G G maltase G Glucoamylase (maltase) or a-dextrinase G G G a-dextrinase G G G G G G G G G G G

  12. Small intestine Portal for transport of virtually all nutrients Water and electrolyte balance • Enzymes associated with • intestinal surface membranes • Sucrase • a dextrinase • Glucoamylase (maltase) • Lactase • peptidases

  13. Carbohydrate absorption Hexose transporter apical basolateral

  14. 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 incidence • Asian/African Americans – High b 1-4 linkage

  15. Metabolism – the chemical changes that take place in a cell that produce energy and basic materials needed for important life processes • millions of cells • Multiple organs (liver, adipose, heart, brain) • Thousands of enzymes • Various conditions (fed, fasted, exercise, stress)

  16. Carbohydrates • Serve as primary source of energy in the cell • Central to all metabolic processes Glucose Cytosol - anaerobic Hexokinase Pentose Phosphate Shunt Glc-1- phosphate Glucose-6-P glycolysis glycogen Pyruvate

  17. cytosol Pyruvate mitochondria (aerobic) Aceytl CoA FATTY ACIDS Krebs cycle Reducing equivalents AMINO ACIDS Oxidative Phosphorylation (ATP)

  18. Glucose Glucose Glucose No mitochondria Glucose Glycogen Lactate The Full Monty

  19. Fasted State Glucose Need 13.8 kJ/mol ATP = -30 kJ/mol -16.7 kJ/mol G-6-Pase Hexokinase Pentose Phosphate Shunt Glc-1- phosphate Glucose-6-P glycolysis GNG glycogen Pyruvate

  20. Controlling Metabolic Flux 1. Control enzyme levels 2. Control of enzyme activity (activation or inhibition)

  21. Control of enzyme activity Rate limiting step

  22. insulin IR P Protein Kinase B (active) Protein Kinase B (inactive) OH P Glycogen synthase kinase (active) OH P Glycogen synthase kinase (inactive) P OH Glycogen synthase (inactive) Glycogen synthase (active) Glycogen formation

  23. Controlling Metabolic Flux 1. Control enzyme levels 2. 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

  24. Glucose utilization

  25. Stage 1 – postparandial All tissues utilize glucose Stage 2 – postabsorptive KEY – Maintain blood glucose Glycogenolysis Glucogneogenesis Lactate Pyruvate Glycerol AA Propionate Spare glucose by metabolizing fat Stage 3- Early starvation Gluconeogenesis Stave 4 – Intermediate starvation gluconeogenesis Ketone bodies Stage 5 – Starvation

  26. 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

More Related