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Glycolysis: Allowed abbreviations
Glucose Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate Dihydroxyacetone phosphate Glyceraldehyde 3-phosphate 1,3-Bisphosphoglycerate 3-phosphoglycerate 2-phosphoglycerate Phosphoenolpyruvate Pyruvate N/A G-6P F-6P F-1,6BP DHAP G-3P 1,3-BPG 3-PG 2-PG PEP
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Fates of Other Sugars
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GLUCONEOGENESIS
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Synthesis of "new glucose" from common metabolites
Gluconeogenesis Synthesis of "new glucose" from common metabolites Humans consume 160 g of glucose per day 75% of that is in the brain Body fluids contain only 20 g of glucose Glycogen stores yield g of glucose So the body must be able to make its own glucose 3
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Substrates for Gluconeogenesis
Pyruvate, lactate, glycerol, amino acids and all TCA intermediates can be utilized Fatty acids cannot! Why? Most fatty acids yield only acetyl-CoA Acetyl-CoA (through TCA cycle) cannot provide for net synthesis of sugars 4
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Gluconeogenesis Occurs mainly in liver and kidneys
Not the mere reversal of glycolysis for 2 reasons: Energetics must change to make gluconeogenesis favorable (delta G of glycolysis = -74 kJ/mol Reciprocal regulation must turn one on and the other off - this requires something new! 5
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Something Borrowed, Something New
Gluconeogenesis Something Borrowed, Something New Seven steps of glycolysis are retained: Steps 2 and 4-9 Three steps are replaced or bypassed: Steps 1, 3, and 10 (the regulated steps!) The new reactions provide for a spontaneous pathway (G negative in the direction of sugar synthesis), and they provide new mechanisms of regulation Make sure you know the THREE BYPASS STEPS of Gluconeogenesis 6
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1st bypass reaction: Pyruvate → PEP Pyruvate is converted back to PEP in two steps. Not shown here is the transport process: since oxaloacetate is usually found in the mitochondrial matrix, it must be transported out into the cytosol. However, there is no transporter for oxaloacetate.
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1st bypass reaction: Pyruvate → PEP Therefore, oxaloacetate is reduced to malate first using malate dehydrogenase. Malate is transported out into the cytosol and then reoxidized back to oxaloacetate
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2nd bypass reaction: Fructose 1,6-Bisphosphate → Fructose 6-phosphate Technically the reverse of the glycolytic reaction, but it is mediated by a different enzyme.
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Mediated by a different enzyme.
2nd bypass reaction: Glucose 6-Phosphate → Glucose Mediated by a different enzyme.
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Cori cycle
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Pentose Phosphate Pathway
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