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2010-03-02 15:25:28

Fuel Metabolism
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  1. Describe the role of gluconeogenesis in maintenance of normal blood glucose levels.
    Glyconeogenesis is the synthesis of a carbohydrate from a simpler, non carbohydrate such oxaloacetat or pyruvate. There for when glucose levels in the blood are low, gluconeogenesis can replenish glucose levels.
  2. Decribe the conversion of pyruvate to glucose.
    It shares several steps with glycolysis, however there are several key steps only found in gluconeogenisis.

    • Pyruvate carboxylase uses an ATP to add carboxyl group to pyruvate, to make Oxaloacetate.
    • Phosphoenolpyruvate carboxylase uses a GTP molecule to add a phosphate group to OAA, making Phosphoenolpyruvate.

    • Fructose 1,6-bisphosphate hydrolysis the phosphate group from the molecule, yeilding Fructose 6-phosphate, Pi and
    • Glucose-6-phosphatase hyrdrolysis, G-6-P to yeild Glucose.
  3. What is the role of pyruvate carboxylase?
    Pyruvate carboxylase works in conjuction with biotin to add a carboxyl group to pyruvate. First ATP is used to add the carboxyl group to biotin which then transfers the carboxyl group to the pyruvate to make OAA.
  4. What is the role of PEP (phosphoenolpyruvate) carboxylkinase?
    PEP carboxylkinase phosphorilates OAA by using GTP.
  5. How is OAA mout out of the mitochondrial matrix?
    OAA itself cannot pass from the mitochondrial matrix throught the mitochondrial membrane to the cytoplasm. To transport OAA it first must be converted to malate by mitrochondrial malate dehydrogenase, 1 NADH and 1 H+. Malate is then able to pass through the membrane, to the cytoplasm where it is reverted back to OAA, by cytosolic malate dehydrogenase. This also produces 1 NADH and 1 H+
  6. Identify the location of each step in gluconeogenesis.
    Depending upon the origonal substrate for gluconeogeniss, pyruvate vs. lactate the number of steps vary. The pyruvate => OAA always is in the mitochondrial matrix. In the pyruvate pathway, OAA => maltate occurs in the matrix and subsiquent steps occur in the cytosol of the cell. In the lactate pathway, OAA => PEP by mitochondrial PEP carboxylkinase occurs in the mitochondrial matrix, and then PEP is transproted out of the mitochondria.
  7. How does glucagon affect the glycolytic and gluconeogenesis pathways?
    Glucagon inhibts the glycolytic pathway where glucagon stimulates the activation of gluconeogenesis by hormonal regulation. When glucose is scarce, glucagon stimulates protein kinase A, with then activates FBPase 2. This then inhibits glycolysis and promotes gluconeogenesis.