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Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
Lec 7 level 3-nu (carbohydrate metabolism iii)
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Lec 7 level 3-nu (carbohydrate metabolism iii)

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  • 1. Nursing - 7Glycogen metabolism 1
  • 2. Glycogen metabolismFunction of glycogenGlycogen is the storage form of carbohydrates in thehuman body. The major sites of storage are liver and muscle.1. The major function of liver glycogen is to provideglucose during starvation. When blood glucose level lowers, liver glycogen is broken down and helps to maintain blood glucose level.2. The function of muscle glycogen is to act as reservefuel for muscle contraction. Muscle glycogen is depleted after prolonged exercise. 2
  • 3.  After taking food, blood sugar tends to rise, which causes glycogen deposition in liver. About 5 hours after taking food, the blood sugar tends to fall. But, glycogen is lyzed to glucose so that the energy needs are met. After about 18 hours fasting, most of the liver glycogen is depleted, when depot fats are hydrolyzed and energy requirement is met by fatty acid oxidation. 3
  • 4. Glycogen metabolism includes:Glycogenolysis.Glycogenesis. 4
  • 5. GlycogenolysisIt is intracellular breakdown of glycogen to formG-1-P which is converted to G-6-P.Site and steps:Its main site is the cytosol of liver and muscles.It is catalyzed by: glycogen phosphorylase and two other enzymes. 5
  • 6. 1- Glycogen phosphorylase: The enzyme glycogen phosphorylase removes glucose units one at a time from the non-reducing end of the glycogen molecule. The product is glucose-1-phosphate. Phosphorylase sequentially attacks alpha-1,4 glycosidic linkages, till it reaches a branch point. It cannot attack the 1,6 linkage at branch point. 6
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  • 8. 2- Debranching needs two enzymes With the help of glucan transferase and debranching enzyme (alpha-1,6- glucosidase), the branching point is also hydrolysed. This glucose residue is released as free glucose. With the removal of branch, phosphorylase enzyme can now proceed with its action. 8
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  • 10. 3- Phosphoglucomutase: Phosphorylation reaction produces glucose- 1-phosphate while debrancher enzyme releases glucose. The glucose-1-phosphate is converted to glucose-6-phosphate by phosphglucomutase. 10
  • 11. 4- Glucose-6-phosphatase in liver Next, hepatic glucose-6-phosphatase hydrolyzed glucose-6-phosphate to glucose. The product of hepatic glycogenolysis is free glucose. The product of hepatic glycogenolysis is free glucose, which is released to the blood stream. 11
  • 12. 5- Muscle lacks Glucose-6-phosphatase: But muscle will not release glucose to the blood stream, because muscle tissue doesnot contain the Glucose-6-phosphatase. The energy yield from one glucose residue derived from glycogen is 3 ATP molecules, because no ATP is required for initial phosphorylation of glucose (step 1 of glycolysis). If glycolysis starts from free glucose only 2 ATPs are produced. 12
  • 13. Glycogenesis The glycogen synthesis occurs by a pathway distinctly different from the reversal of glycogen breakdown. It is the intracellular synthesis of glycogen from glucose.Site and steps: The main site is the cytosol of liver and muscle cells. In the liver it forms 8-10% of its wet weight and in muscle it forms 1-2% of its wet weight. Most other cells may store minute amounts. 13
  • 14. 1- Activation of Glucose: UDP glucose is formed from glucose-1-phosphate and UTP (uridine triphosphate) by the catalytic activity of UDP-glucose pyrophosphorylase. UDP-glucose- pyrophosphorylase Glucose-1- -------------------------------→ UDP-glucosePhosphate + + UTP PPi 14
  • 15. 2- Glycogen synthase: In the next step, activated glucose units are sequentially added by the enzyme glycogen synthase. The glucose unit from UDP-glucose is transferred to a glycogen primer molecule. Glycogen primer (n)----------→ Glycogen (n+1) + + UDP-glucose UDP 15
  • 16.  The glucose unit is added to the nonreducing (outer) end of the glycogen to form an alpha- 1,4-glycosidic linkage and UDP is liberated. The primer is essential as the acceptor of the glycosyl unit. The glycogen primer is formed by glycosylation of glycogenin (a dimeric protein). This molecule acts as the glycogen primer to which glucose units are added by glycogen synthase. 16
  • 17. 3- Brancher enzyme A branching enzyme is needed to create the alpha-1,6 linkages. To this newly created branch, further glucose units can be added in alpha-1,4 linkage by glycogen synthase. Branching makes the molecule more globular. 17
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  • 19. Regulation The key enzyme for glycogenolysis is phosphorylase, which is activated by glucagon and adrenaline, under the stimulus of hypoglycemia. The key enzyme for glycogen synthesis is glycogen synthase, the activity of which is decreased by adrenaline but is enhanced by insulin, under the stimulus of hyperglycemia. 19
  • 20. Glycogen storage diseases These are inborn-errors of metabolism; the word is coined by Garrod in 1908.Glycogen Storage Disease Type-I: It is also called Von Gierke’s disease. Most common type of glycogen storage disease is type I. 20
  • 21.  Incidence is 1 in 100,000 live births. Glucose-6-phosphatase is deficient. Fasting hypoglycemia that does not respond to stimulation by adrenaline. The glucose cannot be released from the liver during over night fasting. Hyperlipidemia, lactic acidosis and ketosis. Glycogen gets deposited in liver. Massive liver enlargement may lead to cirrhosis. Children usually die in early childhood. Treatment is to give small quantity of food at frequent intervals. 21
  • 22. Hexose Monophosphate pathway (HMP) or pentose phosphate pathway (PPP) or pentose pathway (shunt ) 22
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