This is the glycolysis component of Bioc (chem) 361 at UAE University. Some from Campbell 6th ed and the rest from General, Organic, and Biochemistry, 5th edition (2007), by K.J.Denniston, J.J.Topping, and R.L.Caret.

1. Mary K. Campbell
Shawn O. Farrell
http://academic.cengage.com/chemistry/campbell
Chapter 17
Glycolysis
Paul D. Adams • University of Arkansas

2. The Overall Pathway of Glycolysis
• Glycolysis is the first stage of glucose metabolism
• One molecule of glucose is converted to fructose-
1,6-bisphosphate, which gives rise to two molecules
of pyruvate
• It plays a key role in the way organisms extract
energy from nutrients
• Once pyruvate is formed, it has one of several fates

3. Glycolysis Overview
• The anaerobic oxidation of glucose to give
two molecules of pyruvate
• Glucose + 2 ADP + 2 Pi + 2 NAD+
2 pyruvate + 2 ATP + 2 NADH + 2 H+ + 2
H2O
• Pyruvate used in follow-up reactions to
sustain glycolysis
• NADH must be reoxidized so that glycolysis
can continue

5. Fates of Pyruvate From Glycolysis

6. The Reactions of Glycolysis
• Phosphorylation of glucose to give glucose-6-
phosphate
• Isomerization of glucose-6-phosphate to give
fructose-6-phosphate
• Phosphorylation of fructose-6-phosphate to yield
fructose-1,6-bisphosphate
• Cleavage of fructose-1,6,-bisphosphate to give
glyceraldehyde-3-phosphate and dihyroxyacetone
phosphate
• Isomerization of dihyroxyacetone phosphate to give
glyceraldehyde-3-phosphate

7. The Reactions of Glycolysis (Cont’d)
• Oxidation of glyceraldehyde-3-phosphate to give
1,3-bisphosphoglycerate
• Transfer of a phosphate group from 1,3-
bisphosphoglycerate to ADP to give 3-
phosphoglycerate
• Isomerization of 3-phosphoglycerate to give 2-
phosphoglycerate
• Dehydration of 2-phosphoglycerate to give
phosphoenolpyruvate
• Transfer of a phosphate group from
phosphoenolpyruvate to ADP to give pyruvate

8. Conversion of Glucose to Glyceraldehyde-
3-Phosphate (Cont’d)
• Fructose-1,6-bisphosphate is split into two 3-carbon
fragments
• Reaction catalyzed by aldolase
• Side chains of an essential Lys and Cys play key
roles in catalysis

9. Conversion of Glucose to Glyceraldehyde-
3-Phosphate (Cont’d)
• In step 5, dihydroxyacetone phosphate (DHAP) is converted
to glyceraldehyde-3-phosphate
• These compounds are trioses
• This reaction has small +∆G (0.58kcal/mol-1)
• Remember that glycolysis has several reactions that have
very negative ∆G values, and drive other reactions to
completion, so that the overall process is negative

10. Glycolysis Reactions 1 and 2
Reaction 1 (INVESTMENT 1)
• Substrate glucose is phosphorylated by
hexokinase
• Product is glucose-6-phosphate
• Source of the phosphoryl group is ATP
• Expenditure of ATP early in the pathway works as
energy “debt” necessary to get the pathway started
• Not reversible
Reaction 2
• Product of reaction 1 is rearranged to the
structural isomer fructose-6-phosphate by
enzyme phosphoglucose isomerase
• Product has an “exposed” C-1, no longer part of
the ring structure
• Converts and aldose to a ketose

11. Glycolysis: Step 1, 2
Glucose Glucose-6-phosphate
CH2 OH 2-
H O H CH2 OPO3
H Hexokinase H O H
OH H H
HO OH OH H
H OH HO OH
H OH
+ ATP 2- +
CH2OPO3 ADP
O CH2OH
H HO
Fructose-6- H OH Phosphoglucose
phosphate OH H isomerase

12. Glycolysis: Step 2

13. Glycolysis Reaction 3
Reaction 3 (INVESTMENT 2)
• Substrate fructose-6-phosphate is
phosphorylated by phosphofructokinase
• Product is fructose-1,6-bisphosphate
• Source of the phosphoryl group is ATP
• Again the expenditure of ATP early in the
pathway works as energy “debt” necessary to
get the pathway started
• Step 1 and 3 considered the first
committed steps of glycolysis, not
reversible

14. Glycolysis: Step 3
Fructose-6-phosphate
2-
CH2OPO3
O CH2OH Phosphofructokinase
H HO
H CH2O PO3
2-
OH 2-
OH H O CH2OPO3
H HO
+ ATP H
OH
+ ADP
OH H
Fructose-1,6-bisphosphate

15. Phosphofructokinase is a Key Regulatory
Enzyme in glycolysis
• Phosphofructokinase (PFK):
• Exists as a tetramer and subject to allosteric feedback
• The tetramer is composed of L and M subunits
• M4, M3L, M2L2, ML3, and L4 all exist. Combinations of
these subunits are called isozymes
• Muscles are rich in M4; the liver is rich in L4
• ATP is an allosteric effector; high levels inhibit the
enzyme, low levels activate it
• Fructose-1,6-bisphosphate is also an allosteric
effector

16. PFK can exist in Many Isozyme Forms

17. Glycolysis Reactions 4 and 5
Reaction 4
• Product of reaction 3 is split into two 3-carbon
intermediates by the enzyme aldolase forming:
• Glyceraldehyde-3-phosphate (substrate of next
reaction)
• Dihydroxyacetone phosphate
Reaction 5
• Dihydroxyacetone phosphate is rearranged into a
second glyceraldehyde-3-phosphate by the
enzyme triose phosphate isomerase
• Glyceraldehyde-3-phosphate is the only substrate for
the next reaction

18. Glycolysis: Steps 4 and 5
D-glyceraldehyde-
Fructose-1,6-bisphosphate 3-phosphate
2-
CH2OPO3 HC O
2-
O CH2OPO3 H C OH
2-
H HO Aldolase CH2OPO3
H
OH +
2-
OH H CH2O PO3
Triosephosphate C O
isomerase CH2OH
HC O Dihydroxyaceton
H C OH e
2-
D-glyceraldehyde- CH2OPO3 phosphate
3-phosphate

19. Glycolysis: Steps 4 and 5

20. Glycolysis Reaction 6
Reaction 6 (remember this reaction and 7,8,9,10 all happen twice
per glucose)
• Substrate glyceraldehyde-3-phosphate is
oxidized to a carboxylic acid by glyceraldehyde-
3-phosphate dehydrogenase
• Reduces NAD+ to NADH (substrate is oxidized, but not oxidative
phosphorylation|)
• Transfers an inorganic phosphate group to the
carboxyl group
• First step in glycolysis to “harvest” energy (x2)
• Product is 1,3-Bisphosphoglycerate
• New phosphate group attached with a “high-energy”
bond
• This and all subsequent steps occur twice for each
G-3-P

21. Glycolysis: Step 6
Glyceraldehyde
HC O 3-phosphate
dehydrogenase O
H C OH
2-
CH2OPO3
2- C OPO3
+ NAD+ H C OH
2-
+ HPO42- CH2OPO3
Glyceraaldehyde- + NADH + H+
3-phosphate
Glycerate-
1,3-bisphosphate

22. Glycolysis: Step 6

23. Glycolysis Reactions 7 and 8
Reaction 7
• Harvest energy in the form of ATP
• 1,3-Bisphosphoglycerate high energy phosphate
group is transferred to ADP by phosphoglycerate
kinase:
• 3-Phosphoglycerate
• ATP
• This is the first substrate level phosphorylation of
glycolysis (we are now out of debt!)
Reaction 8
• 3-Phosphoglycerate is isomerized into 2-
phosphoglycerate by the enzyme
phosphoglycerate mutase
• Moves the phosphate group from carbon-3 to carbon-2

24. Glycolysis: Steps 7 and 8
1,3-Bisphosphoglycerate
O 3-Phosphoglycerate
2- O
C OPO3 Phosphoglycerate
C O
H C OH kinase + ATP
2-
H C OH
CH2OPO3 CH2OPO3
2-
+ ADP O
C O Phosphoglycerate
2- mutase
H C OPO3
CH2OH
2-Phosphoglycerate

25. Glycolysis Reactions 9 and 10
Reaction 9
• The enzyme enolase catalyzes dehydration of 2-
phospholgycerate
• Phosphoenolpyruvate
• Energy rich – highest energy phosphorylated compound
in metabolism
Reaction 10
• Final substrate-level dehydration in the pathway
• Phosphoenolpyruvate serves as donor of the
phosphoryl group transferred to ADP by pyruvate
kinase making ATP and releasing water
• Pyruvate is the final product of glycolysis
• A coupled reaction in which hydrolysis of the
phosphoester bond provides energy for the formation
of the phosphoanhydride bond of ATP

26. Glycolysis: Steps 9 and 10
“High
2-Phosphoglycerate
O energy
O
C O bond”
C O
2- Enolase
2-
H C OPO3 C O PO3
CH2 OH CH2 + H2O
Phosphoenolpyruvate
O
C O Pyruvate
C O + ATP kinase
CH3
Pyruvate

27. Summary
• In the first stages of glycolysis, glucose is converted
to two molecules of glyceraldehyde-3-phosphate
• The key intermediate in this series of reactions is
fructose-1,6-bisphosphate. The enzyme that
catalyzes this reaction, phosphofructokinase, is
subject to allosteric control

28. Anaerobic Metabolism of Pyruvate
• Under anaerobic conditions, the most important pathway for
the regeneration of NAD+ is reduction of pyruvate to lactate
• Lactate dehydrogenase (LDH) is a tetrameric isoenzyme
consisting of H and M subunits; H4 predominates in heart
muscle, and M4 in skeletal muscle

29. NAD+ Needs to be Recycled to Prevent
Decrease in Oxidation Reactions

30. Fermentation
• From glycolysis pyruvate remains for further
degradation and NADH must be reoxidized
• In aerobic conditions, both will occur in cellular
respiration (mitochondria, TCA, Ox-phos)
• Under anaerobic conditions, fermentation
reactions accomplish this
• Fermentation reactions are catabolic reactions
occurring with no net oxidation
• Major fermentation pathways:
• Lactate fermentation
• Alcohol fermentation

31. Lactate Fermentation
• Lactate fermentation is the anaerobic
metabolism that occurs in exercising muscle
• Bacteria also use lactate fermentation
• Production of yogurt and cheese
• This reaction produces NAD+ and degrades
pyruvate (allowing glycolysis to continue)

32. Alcohol Fermentation
• Yeast ferment sugars of fruit and grains
anaerobically, using pyruvate from glycolysis
• Pyruvate decarboxylase removes CO2 from the
pyruvate producing acetaldehyde
• Alcohol dehydrogenase catalyzes reduction of
acetaldehyde to ethanol, releasing NADH in the
process