Gluconeogenesis is the process by which glucose is synthesized from non-carbohydrate precursors like lactate, amino acids, and glycerol. It is important for maintaining blood glucose levels. While some steps are reversible versions of glycolysis, gluconeogenesis must bypass three irreversible steps in glycolysis using unique enzymes. The key enzyme is pyruvate carboxylase, which fixes carbon in the mitochondria as the first step. Oxaloacetate is the starting material for gluconeogenesis, derived from substrates that enter the pathway in the cytoplasm or mitochondria. Gluconeogenesis requires energy input from ATP or GTP hydrolysis to complete some steps not possible through glycolysis alone.

1. Key knowledge base & conceptual questions
• In what sense can gluconeogenesis be considered a reversal of the
glycolytic pathway? Why can it be said that glycolysis gives energy
which gluconeogenesis takes energy? Why is it important to prevent
gluconeogenesis when the cell is low on ATP?
• Know the three steps of glycolysis which are bypassed by enzymes of
gluconeogenesis. Know which of the glycolysis steps requires ATP,
GTP, and/or NADH.
• Know the 4 reactions that ‘reverse’ the three steps above. Know which
of these steps requires ATP, GTP, and/or NADH.
• Why can oxaloacetate be said to be ‘starting material’ for
gluconeogenesis? How is oxaloacetate derived from lactate, amino
acids, and glycerol?
• For pyruvate carboxylase, know the general features of its (a) location,
(b) mechanism, and (3) regulation. Why is this enzyme the key to
understanding regulation of gluconeogenesis? Know does this enzyme
connect intermediates in glycolysis and in the CAC?
© Sunyoung Kim 2008

2. Overview:
Introduction
Glycolysis
Gluconeogenesis
Glucose
Pyruvate
NADH + H+
+
ATP
Gluconeogenesis
• anabolic process by which glucose is
synthesized from smaller molecules such
as lactate and pyruvate
• important for maintenance of blood
glucose levels within critical limits
© Sunyoung Kim 2008

3. Overview:
Glucose
Energy
Ribose
5-phosphate Glucose
Pyruvate
NADH + H+
+
ATP
Glycogen
Disaccharides
Glucose
• major energy source
for most tissues
• brain alone uses more
than 100 g/day
• can be stored as
glycogen or used for
biosynthesis.
© Sunyoung Kim 2008

4. Gluconeogenesis
Glycolysis
2 pyr + 4 ATP + 2 GTP + 2 NADH
+ 2H+ + 2 H2O
glucose + 4 ADP + 2 GDP + 6 Pi
+ 2 NAD+
glucose + 2 ADP + 2 Pi + 2 NAD+
2 pyr + 2 ATP + 2 NADH + 2H+ +
2 H2O
Glucose
Pyruvate
Lactate
Glucose
Pyruvate
Lactate
Lactate
© Sunyoung Kim 2008

5. • Key intermediate oxaloacetate,
i.e. starting material for pathway
COO
C O
CH2
COO-
• Substrates are lactate, amino
acids, or glycerol.
Gluconeogenesis
© Sunyoung Kim 2008

6. is NOT a reversal of glycolysis
involves reversal of some glycolytic steps
and some unique steps
Three steps in glycolysis are NOT reversible:
Glu + ATP G-6-P + ADP
F-6-P + ATP F-1,6-BP + ADP
PEP + ADP pyr + ATP
Gluconeogenesis
© Sunyoung Kim 2008

7. Four unique gluconeogenesis reactions are
catalyzed by:
1. Pyruvate carboxylase
2. PEP carboxykinase
3. fructose 1,6-bisphosphatase
4. glucose 6-phosphatase
Gluconeogenesis
© Sunyoung Kim 2008

8. Pathway: Location
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9. Pathway: First Step
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10. Pathway: escape from mitochondria
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11. Pathway: in the cytoplasm
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12. Pathway: PEP
The second unique enzyme of gluconeogenesis, phosphoenolpyruvate
(PEP) carboxykinase, converts oxaloacetate to PEP.
© Sunyoung Kim 2008

13. Pathway: Review
© Sunyoung Kim 2008

14. Pathway: reversal
Gluconeogenesis steps up to
generation of fructose-1,6-bisphosphate
uses same enzymes as glycolysis.
Phosphoenolpyruvate
Fructose-1,6-bis-P
© Sunyoung Kim 2008

15. Pathway:
phosphate cleavage
Reversal of the phosphofructokinase step is
provided by fructose 1,6-bisphosphatase.
© Sunyoung Kim 2008

16. Pathway: finish line
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17. Recognize enzymes that use up 4 ATP and
2 GTP in this pathway
1. Pyruvate carboxylase
2. PEP carboxykinase
3. Phosphoglycerate kinase
Gluconeogenesis
© Sunyoung Kim 2008