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17 Cards in this Set

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Gluconeogenesis is
the synthesis of glucose from non-carbohydrate sources
In mammals, the glucose produced passes into
the blood to supply other tissues (cycles body ↔ liver)
In plants, glucose and its derivatives are
precursors for the synthesis of plant cell walls, nucleotides, etc
Gluconeogenesis and glycolysis are ___________ pathways running in opposite directions
NOT IDENTICAL
_____ of the ten enzymatic reactions of gluconeogenesis are the reverse of glycolytic reactions
Seven
Pyruvate ~~~> Phosphoenol Pyruvate (PEP)Cannot occur by reversal of pyruvate kinase reaction of glycolysis because
- Large standard free energy change
- Irreversible under physiological conditions
Pyruvate ~~~> Phosphoenol Pyruvate (PEP)Requires how many rxns?
two exergonic reactions
Pyruvate ~~~> Phosphoenol Pyruvate (PEP) Requires two exergonic reactions. What is the first pathway?
Predominant pathway when pyruvate or alanine is the glucogenic precursor
Pyruvate ~~~> Phosphoenol Pyruvate (PEP) Requires two exergonic reactions. What is the secondary pathway?
A second pathway predominates when lactate is the glucogenic precursor
Pyruvate ~~~> Phosphoenol Pyruvate (PEP) Requires two exergonic reactions. What is the first exergonic step?
- Pyruvate is transported from cytosol to mitochondria

- Pyruvate carboxylase converts it to oxaloacetate
Pyruvate ~~~> Phosphoenol Pyruvate (PEP) Requires two exergonic reactions. What is the second exergonic step?
In the cytosol, oxaloacetate is converted to PEP by PEP CarboxyKinase (PEPCK)
Paths From Pyruvate to Phosphoenol Pyruvate

If PEPCK is only cytosolic then
OAA in the mitochondrion has to be reduced to malate which leaves the mitochondrion (goes back to the cytosol) and is reoxidized to OAA that is converted to PEP by the cytosolic PEPCK
Paths From Pyruvate to Phosphoenol Pyruvate

If both pyruvate carboxylase and PEPCK are mitochondrial then
PEP is formed in the mitochondrion and is transported into the cytosol
Paths From Pyruvate to Phosphoenol Pyruvate

When the PEPCK is in the cytosol and mitochondria as in humans ....
both pathways are used.
Glycolysis: Cost
Glycolysis Generates energy
Gluconeogenesis: Cost
- Requires six high energy
phosphate groups

4 x ATP
2 x GTP

- Requires reductive energy
NADH + H+
Gluconeogenesis can only occur in what organ?
the liver
the essential enzymes required for the reverse pathway is only found in the liver (and to a very small extent, the kidney - rare)