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Gluconeogenesis

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Gluconeogenesis Key knowledge base & conceptual questions • In what sense can gluconeogenesis be considered a reversal of the glycolytic pathway? Why can it be said that glycolysis gives energy which gluconeogenesis takes energy? Why is it important to prevent gluconeogenesis when the cell is low on ATP? • Know the three steps of glycolysis which are bypassed by enzymes of gluconeogenesis. Know which of the glycolysis steps requires ATP, GTP, and/or NADH. • Know the 4 reactions that ‘reverse’ the three steps above. Know which of these steps requires ATP, GTP, and/or NADH. • Why can oxaloacetate be said to be ‘starting material’ for gluconeogenesis? How is oxaloacetate derived from lactate, amino acids, and glycerol? • For pyruvate carboxylase, know the general features of its (a) location, (b) mechanism, and (3) regulation. Why is this enzyme the key to understanding regulation of gluconeogenesis? Know does this enzyme connect intermediates in glycolysis and in the CAC? © Sunyoung Kim 2008 Gluconeogenesis • anabolic process by which glucose is Overview: synthesized from smaller molecules such as lactate and pyruvate Introduction • important for maintenance of blood glucose levels within critical limits G Glucose lu c o is s n e ly + NADH + H o o c + g e ly ATP n G e s Pyruvate is © Sunyoung Kim 2008 Glycogen Overview: Glucose Energy Ribose Disaccharides 5-phosphate Glucose Glucose + NADH + H • major energy source + for most tissues ATP • brain alone uses more than 100 g/day Pyruvate • can be stored as glycogen or used for biosynthesis. © Sunyoung Kim 2008 G Glucose Glucose lu c o is n s e ly o o g c e ly Pyruvate n Pyruvate e G s is Lactate LLaaccttaattee + 2 pyr + 4 ATP + 2 GTP + 2 NADH glucose + 2 ADP + 2 Pi + 2 NAD + + 2H + 2 H2O 2 pyr + 2 ATP + 2 NADH + 2H+ + glucose + 4 ADP + 2 GDP + 6 P 2 H O i 2 + 2 NAD+ © Sunyoung Kim 2008 Gluconeogenesis • Key intermediate oxaloacetate, i.e. starting material for pathway COO C O CH2 COO- • Substrates are lactate, amino acids, or glycerol. © Sunyoung Kim 2008 Gluconeogenesis is NOT a reversal of glycolysis involves reversal of some glycolytic steps and some unique steps Three steps in glycolysis are NOT reversible: Glu + ATP G-6-P + ADP F-6-P + ATP F-1,6-BP + ADP PEP + ADP pyr + ATP © Sunyoung Kim 2008 Gluconeogenesis Four unique gluconeogenesis reactions are catalyzed by: 1. Pyruvate carboxylase 2. PEP carboxykinase 3. fructose 1,6-bisphosphatase 4. glucose 6-phosphatase © Sunyoung Kim 2008 Pathway: Location © Sunyoung Kim 2008 Pathway: First Step © Sunyoung Kim 2008 Pathway: escape from mitochondria © Sunyoung Kim 2008 Pathway: in the cytoplasm © Sunyoung Kim 2008 Pathway: PEP The second unique enzyme of gluconeogenesis, phosphoenolpyruvate (PEP) carboxykinase, converts oxaloacetate to PEP. © Sunyoung Kim 2008 Pathway: Review © Sunyoung Kim 2008 Pathway: reversal Fructose-1,6-bis-P Gluconeogenesis steps up to generation of fructose-1,6-bisphosphate uses same enzymes as glycolysis. Phosphoenolpyruvate © Sunyoung Kim 2008 Pathway: phosphate cleavage Reversal of the phosphofructokinase step is provided by fructose 1,6-bisphosphatase. © Sunyoung Kim 2008 Pathway: finish line © Sunyoung Kim 2008 Gluconeogenesis Recognize enzymes that use up 4 ATP and 2 GTP in this pathway 1. Pyruvate carboxylase 2. PEP carboxykinase 3. Phosphoglycerate kinase © Sunyoung Kim 2008.
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