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