CARBOHYDRATE METABOLISM

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CARBOHYDRATE METABOLISM

• Kadek Rachmawati, M.Kes.,Drh

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CARBOHYDRATE DIGESTION

• AMYLUM digestion by amylase enzyme

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Disaccharides digestion
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• Glucose is the most important carbohydrate
• Glucose is the major metabolic fuel of mammals,
  except ruminants
• Monosaccharide from diet
• - Glucose
• - Fructose
• - Galactose
• Fructose and Galactose glucose at the
  liver

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Galactose Metabolism
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Fructose Metabolism
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• Blood glucose carbohydrate metabolism
  exist are
• 1. Glycolisis
• 2. Glycogenesis
• 3. HMP Shunt
• 4. Oxidation of Pyruvate
• 5. Krebs Cycle
• 6. Change to lipids
• Fasting blood glucose carbohydrate
  metabolism
• 1. Glycogenolisis
• 2. Gluconeogenesis

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GLYCOLISIS

• Glycolisis oxidation of glucose
  energy
• It can function either aerobically or
  anaerobically
• pyruvate
  lactate
• Occurs in the cytosol of all cell
• AEROBICALLY GLYCOLYSIS
• Pyruvate Mitochondria
  oxidized to Asetil CoA Krebs Cycle
  
• CO2 H2O ATP

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Glycolisis
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• Most of the reaction of glycolysis are
  reversible, except of three reaction
• 1. Glucose Glucose-6-phosphate,
  catalyzed by Hexokinase / Glucokinase
• Hexokinase
• - Inhibited allosterically by its product
  glucose-6-p
• - Has a high affinity for its substrate
  glucose
• - available at all cell, except liver and islet
  cell

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• Glucokinase
• - available at liver and islet cell
• - in the liver to remove glucose from
  the blood after meal
• 2. Fructose-6-P Fructose-1,6-biP
• - catalyzed by Phosphofructokinase enzyme
• - Irreversible
• - Rate limiting enzyme in glycolysis
• 3. Phosphoenolpyruvate Enol
  Pyruvate
• - Catalyzed by Pyruvate kinase enzyme
• Oxidation of 1 mol glucose 8 mol ATP and
  2 mol Pyruvate

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• ANAEROBICALLY GLYCOLYSIS
• - The reoxidation of NADH through the
  respiratory chain to oxygen is prevented
• - Pyruvate is reduced by the NADH to lactate,
  by Lactate dehidrogenase enzyme
• Lactate
  dehydrogenase
• Pyruvate NADH H Lactate
  NAD
• - Oxidation 1 mol glucose via anaerobically
  glycolysis 2 mol ATP

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• ANAEROBICALLY GLYCOLYSIS
• Respiratory chain is absence
• Reoxidation of NADH NAD via
  Respiratory chain is inhibited
• Reoxidation of NADH via lactate formation
  allows glycolysis to proceed in the absence of
  oxygen by regenerating sufficient NAD

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GLYCOLYSIS IN ERYTHROCYTE

• Erythrocyte lack mitochondria
  respiratory chain and Krebs cycle are absence
• Always terminates in lactate
• In mammals the reaction catalyzed by
  phosphoglycerate kinase may be bypassed by a
  process that catalyzed Biphosphoglycerate muta-
• se
• Its does serve to provide 2,3-biphosphoglycerate
• bind to hemoglobin decreasing its
  affinity for oxygen oxygen readily
  available to tissues

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GLYCOLYSIS IN ERYTHROCYTE
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OXIDATION OF PYRUVATE

• Occur in mitochondria
• Oxidation of 1 mol Pyruvate 1 mol
  Asetyl-CoA 3 mol ATP
• CH3COCOOH HSCoA NAD CH3CO-SCoA NADH
• (Pyruvate) (Asetyl-CoA)
• Catalyzed by Pyruvate dehydrogenase enzyme
• This enzyme need CoA as coenzyme
• In Thiamin deficiency, oxydation of pyruvate is
  impaired lactic and pyruvic acid

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OXIDATION OF PYRUVATE
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GLYCOGENESIS

• Synthesis of Glycogen from glucose
• Occurs mainly in muscle and liver cell
• The reaction
• Glucose Glucose-6-P
• Hexokinase / Glucokinase
• Glucose-6-P Glucose-1-P
• Phosphoglucomutase
• Glucose-1-P UTP UDPG Pyrophosphate
• UDPG Pyrophosphorylase

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GLYCOGENESIS

• Glycogen synthase catalyzes the formation of
  a-1,4-glucosidic linkage in glycogen
• Branching enzyme catalyzes the formation of
  a-1,6-glucosidic linkage in glycogen
• Finally the branches grow by further
  additions of 1 ? 4-gucosyl units and further
  branching (like tree!)

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SYNTHESIS OF GLYCOGEN
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SYNTHESIS OF GLYCOGEN
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GLYCOGENESIS AND GLYCOGENOLYSIS PATHWAY
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Glycogenesis Glycogenolysis
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GLYCOGENOLYSIS

• The breakdown of glycogen
• Glycogen phosphorilase catalyzes cleavage of the
  1?4 linkages of glycogen to yield
  glucose-1-phosphate
• a(1?4)?a(1?4) glucan transferase transfer a
  trisaccharides unit from one branch to the other
• Debranching enzyme hydrolysis of the 1?6 linkages
• The combined action of these enzyme leads to the
  complete breakdown of glycogen.

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GLYCOGENOLYSIS

• Phosphoglucomutase
• Glucose-1-P Glucose-6-P
• Glucose-6-phosphatase
• Glucose-6-P Glucose
• Glucose-6-phosphatase enzyme a spesific
  enzyme in liver and kidney, but not in muscle
• Glycogenolysis in liver yielding glucose
  export to blood to increase the blood glu-
• cose concentration
• In muscle glucose-6-P glycolysis

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GLUCONEOGENESIS

• Pathways that responsible for converting
  noncarbohydrate precursors to glucose or glycogen
• In mammals occurs in liver and kidney
• Major substrate
• 1. Lactic acid from muscle, erythrocyte
• 2. Glycerol from TG hydrolysis
• 3.Glucogenic amino acid
• 4. Propionic acid in ruminant

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• Gluconeogenesis meets the needs of the body for
  glucose when carbohydrate is not available from
  the diet or from glycogenolysis
• A supply of glucose is necessary especially for
  nervous system and erythrocytes.
• The enzymes
• 1. Pyruvate carboxylase
• 2. Phosphoenolpyruvate karboxikinase
• 3. Fructose 1,6-biphosphatase
• 4. Glucose-6-phosphatase

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GLUCONEOGENESIS
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GLUCONEOGENESIS FROM AMINO ACID
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GLUCONEOGENESIS FROM PROPIONIC ACID
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CORY CYCLE
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HMP SHUNT/HEXOSE MONO PHOSPHATE SHUNT PENTOSE
PHOSPHATE PATHWAY

• An alternative route for the metabolism of
  glucose
• It does not generate ATP but has two major
  function
• 1. The formation of NADPH synthesis of
  fatty acid and steroids
• 2. The synthesis of ribose nucleotide and
  nucleic acid formation

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HMP SHUNT

• Active in liver, adipose tissue, adrenal
  cortex, thyroid, erythrocytes, testis and
  lactating mammary gland
• Its activity is low in muscle
• In erythrocytes
• HMP Shunt provides NADPH for the reduction of
  oxidized glutathione by glutathione reductase
  reduced glutathi-
• one removes H2O2 glutathione peroxidase
  

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HMP SHUNT

• Glutathione reductase
• G-S-S-G 2-G-SH
• (oxidized glutathione) (reduced
  glutathione)
• Glutathione peroxidase
• 2-G-SH H2O2 G-S-S-G 2H2O
• This reaction is important accumulation of
  H2O2 may decrease the life span of the
  erythrocyte damage to the membrane cell
  hemolysis

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HMP SHUNT
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BLOOD GLUCOSE

• Blood glucose is derived from the
• 1. Diet the digestible dietary carbohy-
• drate yield glucose blood
• 2. Gluconeogenesis
• 3. Glycogenolysis in liver
• Insulin play a central role in regulating blood
  glucose blood glucose
• Glucagon blood glucose
• Growth hormone inhibit insulin activity
• Epinefrine stress blood glucose

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