1. Gluconeogenesis Synthesis of "new glucose" from common metabolites
Humans use ~160 g of glucose per day
75% is used by the brain
Body fluids contain only 20 g of glucose
Glycogen stores yield g of glucose
So the body must be able to make its own glucose
90% of gluconeogenesis occurs in the liver and kidneys

2. Figure 18.1 The Glycolysis Pathway

3. Figure 18.1 The Glycolysis Pathway

4. Why is gluconeogenesis not just the reverse of glycolysis?
The reverse of glycolysis is
2 Pyruvate + 2ATP + 2 NADH + 2H+ + 2H20 a
glucose +2ADP +2Pi + 2 NAD + (DG = +74 kJ/mol)
This is thermodynamically unfavorable, so energetically unfavorable steps in the reverse glyolysis reaction are replaced and energy is added in the form of GTP and ATP to give:
The actual equation for gluconeogenesis of
2Pyruvate + 4ATP +2GTP+ 2NADH + 2H+ + 6H20 a
glucose +4ADP +2GDP +6Pi + 2 NAD + (DG = -38 kJ/mol)
Notice the extra ATPs and GTPs drive the process

5. Glycolysis vs Gluconeogenesis
Glycolosis
Glucose (6C) to 2 pyruvates (3C)
Creates energy 2ATP
Reduces 2 NAD+ to 2 NADH
Active when energy in cell low
10 steps from glucose to pyruvate
Pyruvate to AcCoA before Krebs
Gluconeogenesis
2 pyruvates (3C) to Glucose (6C)
Consumes energy 4ATP+2GTP
Oxidizes 2NADH to 2 NAD+
Active when energy in cell high
11 steps from pyruvate to glucose
AcCoA isn’t used in gluconeogenesis
Gluconeogenesis uses 7 of the 10 enzymatic reactions
of glycolysis but in the reverse direction. The 3 not used
are the ones requiring ATP in glycolysis.

6. FIGURE 22. 1 The pathways of gluconeogenesis and glycolysis
FIGURE The pathways of gluconeogenesis and glycolysis. Species in blue, green, and peach-colored shaded boxes indicate other entry points for gluconeogenesis (in addition to pyruvate).

7. The pyruvate carboxylase reaction.
First Reaction of Gluconeogenesis
- recall that pyruvate is the final product of glycolysis.
The pyruvate carboxylase reaction.
(Simplified)

8. Biotin is an essential cofactor in most carboxylation reactions.
It is an essential vitamin in the human diet, but deficiencies are rare.
Avidin, a protein found in egg white binds tightly to biotin and excessive consumption of raw egg white can lead to biotin deficiency.
FIGURE Covalent linkage of biotin to an activesite lysine in pyruvate carboxylase.

9. ATP oxaloacetate Carbonyl phosphate
FIGURE A mechanism for the pyruvate carboxylase reaction. Bicarbonate must be activated for attack by the pyruvate carbanion. This activation is driven by ATP and involves formation of a carbonylphosphate intermediate—a mixed anhydride of carbonic and phosphoric acids. (Carbonylphosphate and carboxyphosphate are synonyms.)
oxaloacetate

10. Pyruvate is converted to oxaloacetate in the mitochondria
Oxaloacetate cannot be transported directly across the mitochondrial membrane so it is converted to malate, then transported, then oxidized back to oxaloacetate.

11. The PEP carboxykinase reaction.

12. Nucleotide diphosphate kinases
Both glycolysis and Oxidative phosphorylation produce ATP with its high energy phoshoanhydride bonds: How does GTP get made from GDP?
Directly from a single step in the Krebs cycle AND from the following reaction
GDP + ATP → GTP + ADP
This is carried out in the cell by an enzyme called
Nucleotide diphosphate kinase which carries out the general reaction
NDP + ATP → NTP + ADP (where N is T, G, or C)

14. FIGURE 22. 1 The pathways of gluconeogenesis and glycolysis
FIGURE The pathways of gluconeogenesis and glycolysis. Species in blue, green, and peach-colored shaded boxes indicate other entry points for gluconeogenesis (in addition to pyruvate). 14

15. Enolase Reaction glycolysis gluconeogenesis Fig. 18-26, p. 595
FIGURE The enolase reaction.
Fig , p. 595

16. FIGURE 22. 1 The pathways of gluconeogenesis and glycolysis
FIGURE The pathways of gluconeogenesis and glycolysis. Species in blue, green, and peach-colored shaded boxes indicate other entry points for gluconeogenesis (in addition to pyruvate). 16

17. The Phosphoglycerate Mutase Reaction
glycolysis
gluconeogenesis
FIGURE The phosphoglycerate mutase reaction.
Fig , p. 594

18. Isomerase: An enzyme that catalyzes the transformation of compounds into their positional isomers. In the case of sugars this usually involves the interconversion of an aldose into a ketose, or vice versa.
Kinase: An enzyme that catalyzes the phosphorylation (or dephosphorylation) of a molecule using ATP (or ADP).
Mutase: An enzyme that catalyzes the transposition of functional groups, such as phosphates, sulfates, etc.

19. FIGURE 22. 1 The pathways of gluconeogenesis and glycolysis
FIGURE The pathways of gluconeogenesis and glycolysis. Species in blue, green, and peach-colored shaded boxes indicate other entry points for gluconeogenesis (in addition to pyruvate). 19

20. Phospoglycerate kinase
glycolysis
gluconeogenesis
FIGURE The phosphoglycerate kinase reaction.
Phospoglycerate kinase
Fig , p. 593

21. FIGURE 22. 1 The pathways of gluconeogenesis and glycolysis
FIGURE The pathways of gluconeogenesis and glycolysis. Species in blue, green, and peach-colored shaded boxes indicate other entry points for gluconeogenesis (in addition to pyruvate). 21

22. The glyceraldehyde-3-phosphate dehydrogenase reaction
glycolysis
gluconeogenesis
FIGURE The glyceraldehyde-3-phosphate dehydrogenase reaction.

23. FIGURE 22. 1 The pathways of gluconeogenesis and glycolysis
FIGURE The pathways of gluconeogenesis and glycolysis. Species in blue, green, and peach-colored shaded boxes indicate other entry points for gluconeogenesis (in addition to pyruvate). 23

24. Triose phosphate isomerase
glycolysis
gluconeogenesis
FIGURE The triose phosphate isomerase reaction.
Triose phosphate isomerase
Fig , p. 589

25. FIGURE 22. 1 The pathways of gluconeogenesis and glycolysis
FIGURE The pathways of gluconeogenesis and glycolysis. Species in blue, green, and peach-colored shaded boxes indicate other entry points for gluconeogenesis (in addition to pyruvate). 25

26. Aldolase 4th reaction of glycolysis (7th reaction of gluconeogenesis).
Reversible reaction also used in gluconeogenesis.
An aldol cleavage reaction (the reverse of an aldol condensation).
glycolysis
gluconeogenesis

28. FIGURE 22. 1 The pathways of gluconeogenesis and glycolysis
FIGURE The pathways of gluconeogenesis and glycolysis. Species in blue, green, and peach-colored shaded boxes indicate other entry points for gluconeogenesis (in addition to pyruvate). 28

31. ANIMATED FIGURE 18.4 Phosphorylation of glucose to glucose- 6-phosphate by ATP creates a charged molecule that cannot easily cross the plasma membrane. See this figure animated at brookscole.com/ggb3
Fig. 18-4, p. 584

32. Glucose-6-phosphatase
enzyme unique to liver and kidney allowing them to supply glucose to other tissues. Found in ER

33. The Cori Cycle

34. Regulation of Gluconeogenesis
Glucose-6-phosphatase is subject to substrate level control.
- at higher G6P concentrations reaction rate increases
- recall, this happens in the liver. Other tissues do not hydrolyze their G6P, thereby trapping it in the cells.
Glycolysis and gluconeogenesis are reciprocally regulated.
- regulatory molecules that inhibit gluconeogenesis often activate glycolysis, and vise versa.

35. A potent allosteric regulatory molecule.
- activates phosphofructokinase.
- inhibits fructose-1,6-bisphosphatase.
- its synthesis and degradation are catalyzed by the same bifunctional enzyme.

36. Fructose-2,6-bisphosphate activates glycolysis and inhibits gluconeogenesis, so its level is very important.

37. F2,6 BP PFK-1 F2,6 BP ATP ADP Pi PFK-2 F2,6 BP INHIBITS STIMULATES
FIGURE The pathways of gluconeogenesis and glycolysis. Species in blue, green, and peach-colored shaded boxes indicate other entry points for gluconeogenesis (in addition to pyruvate). 37

38. 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase

39. Increased phosphorylation
6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase
Low glucose
High glucagon
Increased phosphorylation
Phosphorylation of the enzyme results in the inactivation of the phosphofructokinase-2 activity and activation of the fructose-2,6-bisphosphatase activity. This results in a down regulation of glycolysis and increased gluconeogenesis.

41. Substrates for gluconeogenesis:
Pyruvate
Lactate
TCA cycle intermediates
Most amino acids
Not substrates for gluconeogenesis:
Acetyl-CoA
Fatty acids
Lysine
Leucine

43. Plants and bacteria can make glucose from acetate.