3 introduction to metabolism-pdf

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3 introduction to metabolism-pdf

  1. 1. Three Stages of Metabolism
  2. 2. 3 Stages of Metabolism• First stage:• It is the breakdown & degradation of polysaccharides, proteins & lipids into their simplest units either through intracellular catabolism or during digestion
  3. 3. Carbohydrates Proteins Lipids Glucose Amino acids Free Fatty acids1st Stage of Metabolism
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  7. 7. Digestive juices
  8. 8. Disaccharidase < TARGET="display">
  9. 9. Dipeptide Dipeptidase < TARGET="display">
  10. 10. Lipase < TARGET="display">
  11. 11. CoA.CoA of Kreb’s cycle. & glycerol.
  12. 12. Carbohydrates Proteins Lipids 1st Stage Glucose Amino acids Free Fatty acids 2nd Pyruvate Acetyl CoA Stage ATP(substrate level phosphorylation)1st and 2nd Stages of Metabolism
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  14. 14. Carbohydrates Proteins Lipids 1st Stage Glucose Amino acids Free Fatty acids 2nd Pyruvate Acetyl CoA Stage ATP(Substrate level phosphorylation) NADH/FADH2 3rd Stage Oxidative phosphorylation (CO2 + H2O) + ATP Stages of Metabolism
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  16. 16. The Sun is Energy for Life• Phototrophs use light to drive synthesis of organic molecules (C6H12O6)• Heterotrophs use these organic molecules as building blocks• CO2, O2, and H2O are recycled
  17. 17. MetabolismMetabolism includes: 1. Digestion 2. Absorption 3. Catabolism 4. Anabolism 5. Excretion
  18. 18. Metabolism• Catabolism: degradative pathways, Usually energy- yielding!• Anabolism: biosynthetic pathways, energy-requiring!
  19. 19. Different Types of Metabolic Pathways a) Linear metabolic pathway: The product of each step is the substrate for the next step b) Cyclic pathway forms a closed loop: In the citric acid cycle, an acetyl group is metabolized (oxidized) via reactions that regenerate the intermediates of the cycle c) Spiral pathway: The same set of enzymes catalyze a progressive lengthening of the acyl chain
  20. 20. Different Types of Metabolic Pathways Linear pathway Cyclic pathway Spiral pathway Fatty acid synthesisConversion of 3-phospho- Kreb’sycle glycerate into serine Enz 1 Enz 2 Enz 3
  21. 21. Comparing Pathways• Anabolic & catabolic pathways involving the same product are not the same• Some steps may be common to both• Metabolic pathways are multi-step pathways• This also allows regulation mechanisms to turn on pathway and other turned off
  22. 22. Single-step versus Multi- step Pathways (capturing chemical energy)A • The uncontrolled combustion of glucose releases a largeC amount of energy all at onceE • A multi-step enzyme – catalyzed pathway – releases the same amount of energyF but conserves much of it in a manageable form
  23. 23. Single-step versus Multi- step Pathways (capturing chemical energy)A 1. Multiple points whereC metabolites can enter & leave 2. Multiple points for regulationE 3. Substrates & products can be involved in more than oneF metabolic reaction
  24. 24. Regulation of Metabolic Pathways Starting Substrate Final End Product Final End Product Starting Substrate
  25. 25. Regulation of Metabolic Pathways Irreversible Reactions
  26. 26. Regulation of Metabolic Pathways Feedback Inhibition• Feedback inhibition occurs when a product (usual the final product) of a pathway controls the rate of its own synthesis through inhibition of an early step, usually the first step.
  27. 27. Regulation of Metabolic Pathways Feed-forward Activation• Feed-forward activation occurs when a metabolite produced early in a pathway activates an enzyme that catalyzes a reaction further down the pathway.
  28. 28. Regulation of Metabolic Pathways Coordinated Regulation + • Can serve to deplete intermediates & accelerate their re-supply• The existence of multiple control points is to be expected
  29. 29. Prof. Dr. Mamdouh M. El-Shishtawy
  30. 30. 1. DigestionDigestion of Carbohydrates • It is the breakdown & degradation of polysaccharides & oligosaccharides into their simplest units (Monosaccharides)
  31. 31. Carbohydrates Digestible Do not need digestion Non-DigestibleStarch MonosaccharidesGlycogen Cellulose Pentoses Lactose Hexoses Sucrose
  32. 32. TheDigestive System
  33. 33. PH 6.4 – 6.9. Activated by Cl-, digests starch to Acidic PH of stomach (1-2) is dextrins, maltose & unsuitable for salivary isomaltose amylase 4. - (Activated by Cl ). 3. Brush border (Intestinal juice,Succus Entericus) containing:Maltase, Lactase & Sucrase
  34. 34. Carbohydrate Digestion in Small Intestine• Salivary amylase stops working in acidic stomach (if pH  4.5)• 50% of dietary starch digested before it reaches small intestine• Brush border enzymes act upon oligosaccharides, maltose, sucrose & lactose• lactose indigestible after age 4 in most humans (due to lack of lactase)
  35. 35. Carbohydrate Digestion in Small Intestine
  36. 36. & Isomaltose
  37. 37. 2. Absorption Monosaccharides Absorption• Sodium-glucose transport proteins (SGLT) in membrane help absorption of glucose & galactose• Fructose absorbed by facilitated diffusion then converted to glucose inside the cell
  38. 38. Pentoses absorbed by Passive Diffusion According concentration gradient Hexoses absorbed by Active Transport Against concentration gradientAbsorption of Pentoses & Hexoses
  39. 39. Types of Transport Carriers
  40. 40. Monosaccharides AbsorptionLiver
  41. 41. Digestion of Lactose (Lactase)
  42. 42. Lactose Intolerance• Some individuals [90% of certain races (adult blacks & Orientals)] have a defect in lactase enzyme• Undigested maltose (osmotically active compound) passes to the bowel (large intestine), acted upon by bacteria of large intestine producing short chain fatty acids & CO2 gas, leading to: 1. Abdominal distention (cramping) 2. Abdominal pain 3. Nausea 4. Bloating 5. Watery diarrhea
  43. 43. Lactase deficiency
  44. 44. Fate of Absorbed Glucose• Glucose enter Liver & Brain by Passive diffusion• Glucose enter other tissues (skeletal muscle, adipose tissue, etc…) by Active transport• Active transport is enhanced by Insulin
  45. 45. Utilization of Glucose Anabolic Reactions Catabolic Reactions1) Storage in the form of Glycogen (Glycogenesis)2) Storage in the form of TAG 1) Glycolysis (Lipogenesis) 2) Kreb’s Cycle3) Synthesis of sugar alcohols and amino sugars 3) Pentose Shunt4) Interconversion between 4) Formation of monosaccharides Uronic acids

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