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CARBOHYDRATE BIOSYNTHESIS

CARBOHYDRATE BIOSYNTHESIS. GLUCONEOGENESIS. . Pentose Phosphate. CALVIN CYCLE. . GLYCOGEN SYNTHESIS. PO 4. H 2 O. PO 4. H 2 O. Ribose 5-PO 4. Phosphatase. Blood Glucose. Glycogen. Glucose. G6P. Kinase. F6P. Kinase. Phosphatase. F1,6bisP. Gly-3-P. DHAP. 1,3bisPGA.

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CARBOHYDRATE BIOSYNTHESIS

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  1. CARBOHYDRATE BIOSYNTHESIS GLUCONEOGENESIS  Pentose Phosphate CALVIN CYCLE  GLYCOGEN SYNTHESIS

  2. PO4 H2O PO4 H2O Ribose 5-PO4 Phosphatase Blood Glucose Glycogen Glucose G6P Kinase F6P Kinase Phosphatase F1,6bisP Gly-3-P DHAP 1,3bisPGA Kinase 3PGA 2PGA PEP Kinase Pyruvate OAA L-lactate

  3. Gluconeogenesis Synthesis of glucose de novo (from scratch) An anabolic pathway for the synthesis of glucose from L-lactate or smaller precursors. Significance: Primarily in the liver (80%); kidney (20%) Maintains blood glucose levels The anabolic arm of the Cori cycle

  4. Stage I Gluconeogenesis PEP carboxykinase PEPCK F1,6BP Gly3P DHAP Glycerol 1,3BPGA L-aspartate 3PGA Pyruvate Carboxylase 2PGA 2 OAA L-malate PEP 1 L-lactate Pyruvate OAA L-malate Mitochondria L-alanine

  5. R5P Pentose Phosphate 4 Glycogen Glucose-6-phosphatase Glucose G6P G1P UDP-glucose Hexokinase 3 F6P Fructose 1,6 - bisphosphatase PFK-1 F1,6BP Stage II Gluconeogenesis

  6. PEP Pyruvate F-1,6 bisPO4 F-6-PO4 Glucose-6-PO4 Glucose Problems: 3 irreversible reactions Go’ = -61.9 kJ per mol Go’= -17.2 kJ per mol Go’= -20.9 kJ per mol Take home: Gluconeogenesis feature enzymes that bypass 3 irreversible KINASE steps

  7. Swinging Arm Second Entry Point for Pyruvate Pyruvate carboxylase CO2 Fixation Reactions Biotin’s only function is to fix CO2

  8. O O C- N N O CH2 S CH2 Attach to Enzyme at lysine -amine group CH2 CH2 C=0 HN CH2 CH2 CH2 CH2 C Carboxylase Enzyme Biocytin (the cofactor of biotin) Carboxy Biotin Carboxy group Swinging Arm

  9. GDP GTP COO COO C=O C~O PO3 CH2 CH2 CO2 COO PO4 PO4 3 Bypasses in Gluconeogenesis PEP OAA PEP Carboxykinase H2O Fructose 1,6bisPO4 Fructose-6-PO4 Fructose 1,6 bisphosphatase H2O Glucose-6-PO4 Glucose Glucose 6 phosphatase

  10. Liver is a major anabolic organ L-lactate D-glucose Blood Lactate Blood Glucose THE CORI CYCLE L-lactate D-glucose Muscle is a major catabolic tissue

  11. REGULATION FOCUS ON CARBON FLOW L-lactate (Synthesis) Glucose Glucose Pyruvate (Degradation) ENZYMES (Allosteric, cAMP-dependent, organ-specific isozymes) Rule 1. Allosteric are targets of metabolite regulators (effectors) RECIPROCAL REGULATION Rule 2. Kinases in glycolysis; phosphatases in synthesis Exception: PEPCK in synthesis - cAMP POSTIVE EFFECTORS Rule 3. ATP, citrate, acetyl-CoA, G6P turn on synthesis AMP, F2,6BP,turn on degradation NEGATIVE EFFECTORS Rule 4. ATP, acetyl-CoA, citrate,G6P turn off degradation AMP, F2,6BP turn off synthesis

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