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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 - PowerPoint PPT Presentation
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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 N/A
Fates of Other Sugars
GLUCONEOGENESIS
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 180-200 g of glucose So the body must be able to make its own
glucose
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
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!
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
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.
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
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.
Mediated by a different enzyme.
2nd bypass reaction:Glucose 6-Phosphate → Glucose
Cori cycle
Pentose Phosphate Pathway
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