Download Other Sugars, Gluconeogenesis, PPP

Glycolysis: Allowed abbreviations
 Glucose
 N/A
 Glucose 6-phosphate
 G-6P
 Fructose 6-phosphate
 F-6P
 Fructose 1,6-bisphosphate
 F-1,6BP
 Dihydroxyacetone phosphate
 DHAP
 Glyceraldehyde 3-phosphate
 G-3P
 1,3-Bisphosphoglycerate
 1,3-BPG
 3-phosphoglycerate
 3-PG
 2-phosphoglycerate
 2-PG
 Phosphoenolpyruvate
 PEP
 Pyruvate
 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.
2nd bypass reaction:
Glucose 6-Phosphate → Glucose
Mediated by a different enzyme.
Cori cycle
Pentose Phosphate Pathway