1. Glycolysis Under Anaerobic Conditions
“Anaerobic” Glycolysis
2 ADP + 2 Pi
2 ATP
glucose
2 lactate
Hydrolysis of ATP Produced:
DGo´ = 2 x -7.3 = kcal/mol
Complete Oxidation of Glucose
DGo´ = -686 kcal/mol

2. Glycolysis Under Aerobic Conditions
“Aerobic” Glycolysis
2 ADP + 2 Pi
2 ATP
glucose
2 pyruvate
2 NAD+
2 NADH
Catabolism of Glucose by Glycolysis, TCA, and Ox. Phos.
30 ADP + 30 Pi
30 ATP
Glucose + 6 O2
6 CO2 + 6 H2O
Hydrolysis of ATP Produced
DGo´ = 30 x -7.3 = -219 kcal/mol
Complete Oxidation of Glucose O2
DGo´ = -686 kcal/mol

3. Circumstances Under Which the Anaerobic Glycolytic Pathway is Used
1. Anaerobic bacteria
In eukaryotic cells under conditions that are completely
anaerobic (rare)
In aerobic eukaryotic cells under conditions where the
mitochondrial electron transport chain is saturated (w/ reducing
equivalents (NADH, FADH2), pyruvate, or both; common under
conditions of strenuous exercise).

4. Regeneration of NAD+ in the Cytosol
Aerobic Conditions
(Processing of Cytosolic NADH
and Pyruvate by TCA/Oxidative Phosphorylation)
Glycerol Phosphate Shuttle
E-FAD is an enzyme in the inner mitochondrial membrane involved in oxidative phosphorylation

5. Thermodynamics of Glycolysis
Glycolysis is not like this ..
Glycolysis is more like this ..

6. b) DG0 depends only on the identity of the products and reactants
True or False? a)
b) DG0 depends only on the identity of the products and reactants
b) The reaction will always flow in the direction where DG is negative.
c) If DG0 is near 0, then the reaction can be easily driven from backwards by pumping excess product into the reaction. These reactions are called “reversible”.
d) If DG0 is << 0, (such that P/R at any reasonable cellular levels can not reverse the sign of DG), then the reaction is called “irreversible”.

7. Hexokinase Glycolysis Glycogen synthesis Pentose Phosphate Pathway
Irreversible reaction (means that DGo´ is “large” and negative,
DGo´ = -4.0 kcal/mol)
(2) Two forms (isozymes)
(3) Not a major regulatory
enzyme of the pathway
since G-6-P can also
be used for glycogen
synthesis or the pentose
phosphate pathway

8. True or False?
The high Km of liver glucokinase relative to muscle hexokinase means that in the fed state with limiting glucose, the liver glycogen will be replenished before muscle glycogen.
Km is the substrate concentration where the enzyme exhibits ½ maximal velocity.
We normally expect the first irreversible reaction in that pathway that is “committed” to a particular product to be the regulated enzyme.

9. Phosphoglucoisomerase
Reversible reaction (means that DGo´ is close to 0)
(2) F-6-P is NOT irreversibly “committed” to the glycolytic
pathway

10. Phosphofructokinase (PFK)
Irreversible reaction; catalyzes the “committed” step in the pathway
Important regulatory enzyme; regulated allosterically in the
following manner:
Stimulated by AMP and ADP
Inhibited by ATP and Citrate

11. Idealized allosteric feedback inhibition
shift caused by +/- feedback inh.
velocity -I +I
[S]
ambient [S]

12. Aldolase
“Pulled” toward pyruvate

13. Glyceraldehyde-3-phosphate dehydrogenase
(1) Oxidation-reduction reaction (conversion of aldehyde to
carboxylic acid phosphate ester)
(2) 2 NADH are synthesized for each molecule of glucose that
enters the pathway
(3) Reversible (NOTE - NOT all energy yielding reactions are
irreversible)

14. 3-phosphoglycerate kinase
2 ATP are synthesized for each molecule of glucose that
enters the pathway
(2) Reversible
a) Due to the fact that the phosphoryl transfer potentials
of 1,3-bisphosphoglycerate and ATP are comparable
b) Second example of an energy yielding reaction that is
reversible

15. Pyruvate Kinase
(1) Irreversible reaction (DGo´ = -7.5 kcal/mol). Thermodynamically this “pulls” the series of reactions from F-1,6-bisP to pyruvate
(2) Regulates the pathway:
Activated by AMP, ADP, F-1,6-bisP
Inhibited by ATP

16. Regulation of Glycolysis
Irreversible steps of the pathway are potential points of
regulation: hexokinase, PFK, and pyruvate kinase
Pyruvate kinase
Hexokinase
Product inhibition by glucose-6-phosphate
“Substrate” stimulation
by F-1,6-bisP

17. PFK is the Most Important Regulatory Enzyme of the Glycolytic Pathway
“Product” Inhibition:
Citrate Inhibits
Regulation by Energy Charge:
Stimulation by ADP
Allosterically inhibition by ATP
PFK is also regulated by F-2,6-bisphosphate (hormonally controlled)
Surplus of citrate occurs
when the TCA cycle produces
a sufficient amount of ATP