About glycolysis by kamal singh khadka Microbiology and biochemistry

1. GLYCOLYSIS
Kamal Singh Khadka

2. GLYCOLYSIS
It is defined as a sequence of reactions converting
glucose to pyruvate or lactate, with the
production of ATP.
Greek: glykys = sweet; lysis = splitting

3. SALIENT FEATURES OF GLYCOLYSIS
• takes place in all cells of the body
• the enzymes of this pathway are present in cytosol of cells
• in absence of oxygen -anaerobic glycolysis takes place ,
lactate is the end product.
• in presence of oxygen -aerobic glycolysis, pyruvate is the
end product.
•it is also known as Embden-Meyerhof (e.m.) pathway. (
Gustav Embden; Otto Meyerhof; German Biochemists -
elucided the whole pathway in muscle. )

4. • glycolysis is the major pathway for ATP synthesis in
tissues lacking mitochondria.
• glycolysis is very essential for brain.
• the intermediates of glycolysis is used in formation
of non-essential amino acids and glycerol.

5. Hexokinase
Phosphofructokinase
glucose Glycolysis
ATP
ADP
glucose-6-phosphate
Phosphoglucose Isomerase
fructose-6-phosphate
ATP
ADP
fructose-1,6-bisphosphate
Aldolase
glyceraldehyde-3-phosphate + dihydroxyacetone-phosphate
Triosephosphate
Isomerase
Glycolysis continued

6. Glyceraldehyde-3-phosphate
Dehydrogenase
Phosphoglycerate Kinase
Enolase
Pyruvate Kinase
glyceraldehyde-3-phosphate
NAD+
+ Pi
NADH + H+
1,3-bisphosphoglycerate
ADP
ATP
3-phosphoglycerate
Phosphoglycerate Mutase
2-phosphoglycerate
H2O
phosphoenolpyruvate
ADP
ATP
pyruvate

7. H O
OH
H
OHH
OH
CH2OH
H
OH
H H O
OH
H
OHH
OH
CH2OPO3
2
H
OH
H
23
4
5
6
1 1
6
5
4
3 2
ATP ADP
Mg2+
glucose glucose-6-phosphate
Hexokinase
1. Hexokinase catalyzes:
Glucose + ATP  glucose-6-P + ADP
ATP binds to the enzyme as a complex with Mg++.
this is an irreversible reaction.

8. 2. Phosphoglucose Isomerase catalyzes:
glucose-6-P (aldose)  fructose-6-P (ketose)
it also requires Mg++
H O
OH
H
OHH
OH
CH2OPO3
2
H
OH
H
1
6
5
4
3 2
CH2OPO3
2
OH
CH2OH
H
OH H
H HO
O
6
5
4 3
2
1
glucose-6-phosphate fructose-6-phosphate
Phosphoglucose Isomerase

9. 3. phosphofructokinase :
the phosphofructokinase reaction is the rate-limiting
step of glycolysis.
this an irreversible and regulatory step in glycolysis.
PFK is an allosteric enzyme, the activity of which is
controlled by several allosteric enzymes.
CH2OPO3
2
OH
CH2OH
H
OH H
H HO
O
6
5
4 3
2
1 CH2OPO3
2
OH
CH2OPO3
2
H
OH H
H HO
O
6
5
4 3
2
1
ATP ADP
Mg2+
fructose-6-phosphate fructose-1,6-bisphosphate
Phosphofructokinase

10. 4. Aldolase catalyzes: fructose-1,6-bisphosphate 
dihydroxyacetone-P + glyceraldehyde-3-P
6
5
4
3
2
1CH2OPO3
2
C
C
C
C
CH2OPO3
2
O
HO H
H OH
H OH
3
2
1
CH2OPO3
2
C
CH2OH
O
C
C
CH2OPO3
2
H O
H OH+
1
2
3
fructose-1,6-
bisphosphate
Aldolase
dihydroxyacetone glyceraldehyde-3-
phosphate phosphate
Triosephosphate Isomerase

11. 5. triose phosphate isomerase catalyzes:
dihydroxyacetone-p  glyceraldehyde-3-p
it is inhibited by bromohydroxyacetone phosphate.
6
5
4
3
2
1CH2OPO3
2
C
C
C
C
CH2OPO3
2
O
HO H
H OH
H OH
3
2
1
CH2OPO3
2
C
CH2OH
O
C
C
CH2OPO3
2
H O
H OH+
1
2
3
fructose-1,6-
bisphosphate
Aldolase
dihydroxyacetone glyceraldehyde-3-
phosphate phosphate
Triosephosphate Isomerase

12. C
C
CH2OPO3
2
H O
H OH
C
C
CH2OPO3
2
O OPO3
2
H OH
+ Pi
+ H+
NAD+
NADH 1
2
3
2
3
1
glyceraldehyde- 1,3-bisphospho-
3-phosphate glycerate
Glyceraldehyde-3-phosphate
Dehydrogenase
6. glyceraldehyde-3-phosphate dehydrogenase : it is
inhibited by iodoacetate and arsenite.

13. C
C
CH2OPO3
2
O OPO3
2
H OH
C
C
CH2OPO3
2
O O
H OH
ADP ATP
1
22
3 3
1
Mg2+
1,3-bisphospho- 3-phosphoglycerate
glycerate
Phosphoglycerate Kinase
7. phosphoglycerate kinase catalyzes:
1,3-bisphosphoglycerate + ADP 
3-phosphoglycerate + ATP
this step is the good example of substrate level
of phosphorylation since ATP is synthesized without etc.
it is reversible, a rare example of kinase reactions

14. C
C
CH2OH
O O
H OPO3
2
2
3
1
C
C
CH2OPO3
2
O O
H OH2
3
1
3-phosphoglycerate 2-phosphoglycerate
Phosphoglycerate Mutase
8. Phosphoglycerate Mutase catalyzes:
3-phosphoglycerate  2-phosphoglycerate

15. 9. enolase catalyzes:
2-phosphoglycerate phosphoenolpyruvate + H2o
this reaction requires Mg+2 or Mn+2
it is inhibited by Fluoride
C
C
CH2OH
O O
H OPO3
2
C
C
CH2OH

O O
OPO3
2
C
C
CH2
O O
OPO3
2
OH
2
3
1
2
3
1
H
2-phosphoglycerate enolate intermediate phosphoenolpyruvate
Enolase

16. 10. Pyruvate Kinase catalyzes:
phosphoenolpyruvate + ADP  pyruvate + ATP
C
C
CH3
O O
O2
3
1
ADP ATP
C
C
CH2
O O
OPO3
2
2
3
1
phosphoenolpyruvate pyruvate
Pyruvate Kinase
Mg+2

17. ENERGY PRODUCTION AND UTILIZATION
 2 ATP invested
 4 ATP produced (2 from each of two 3C fragments
from glucose)
 Net production of 2 ~P bonds of ATP per glucose.
Glycolysis - total pathway,
glucose + 2 NAD+ + 2 ADP + 2 Pi 
2 pyruvate + 2 NADH + 2 ATP
In aerobic organisms:
 pyruvate produced in Glycolysis is oxidized to CO2 via
Krebs Cycle
 NADH produced in Glycolysis & Krebs Cycle is
reoxidized via the respiratory chain, with production
of much additional ATP.

18. Glycolysis,
glucose + 2 NAD+ + 2 ADP + 2 Pi 
2 pyruvate + 2 NADH + 2 ATP
Fermentation, from glucose to lactate:
glucose + 2 ADP + 2 Pi  2 lactate + 2 ATP
Anaerobic catabolism of glucose yields only 2 “high
energy” bonds of ATP.

19. C
C
CH3
O
O
O
C
HC
CH3
O
OH
O
NADH + H+
NAD+
Lactate Dehydrogenase
pyruvate lactate
E.g., Lactate Dehydrogenase catalyzes reduction of the
keto in pyruvate to a hydroxyl, yielding lactate, as
NADH is oxidized to NAD+.

20. REGULATION OF GLYCOLYSIS
Glycolysis pathway is regulated by control of 3
enzymes :
1) Hexokinase
2) Phosphofructokinase
3) Pyruvate Kinase.

21. Hexokinase is inhibited by product glucose-6-phosphate:
 by competition
 by allosteric interaction
 Has low KM (0.1mM)
.
H O
OH
H
OHH
OH
CH2OH
H
OH
H H O
OH
H
OHH
OH
CH2OPO3
2
H
OH
H
23
4
5
6
1 1
6
5
4
3 2
ATP ADP
Mg2+
glucose glucose-6-phosphate
Hexokinase

22.  Glucokinase has a high KM (10mM) for glucose.
It is active only at high [glucose].
H O
OH
H
OHH
OH
CH2OH
H
OH
H H O
OH
H
OHH
OH
CH2OPO3
2
H
OH
H
23
4
5
6
1 1
6
5
4
3 2
ATP ADP
Mg2+
glucose glucose-6-phosphate
Hexokinase
Glucokinase (
a variant of
Hexokinase) is
found in liver.

23. phosphofructokinase is usually the rate-limiting step of
the glycolysis pathway.
phosphofructokinase is allosterically inhibited by ATP,
citrate, H+
it is allosteric activated by fructose 2,6 bisphosphate,
AMP, Pi
CH2OPO3
2
OH
CH2OH
H
OH H
H HO
O
6
5
4 3
2
1 CH2OPO3
2
OH
CH2OPO3
2
H
OH H
H HO
O
6
5
4 3
2
1
ATP ADP
Mg2+
fructose-6-phosphate fructose-1,6-bisphosphate
Phosphofructokinase

24. C
C
CH3
O O
O2
3
1
ADP ATP
C
C
CH2
O O
OPO3
2
2
3
1
phosphoenolpyruvate pyruvate
Pyruvate Kinase
Pyruvate Kinase, the last
step Glycolysis
Inhibited by ATP
Activated by F1,6-BP

25. Feeder Pathways for Glycolysis
• Many carbohydrates besides glucose meet their
catabolic fate in glycolysis, after being transformed
into one of the glycolytic intermediates.
• The most significant are;
– storage polysaccharides glycogen and starch;
– disaccharides maltose, lactose, trehalose, and
sucrose; and
– monosaccharides fructose, mannose, and
galactose

26. Fig: Feeder pathways of glycolysis

27. Glycogen and Starch Are Degraded by
Phosphorolysis
• Glycogen in animal tissues and in microorganisms
(and starch in plants) can be mobilized for use
within the same cell by a phosphorolytic reaction
catalyzed by glycogen phosphorylase (starch
phosphorylase in plants).

28. Fructose
• D-Fructose, present in free form in many fruits
and formed by hydrolysis of sucrose in the
small intestine of vertebrates, is
phosphorylated by hexokinase
• This is a major pathway of fructose entry into
glycolysis in the muscles and kidney.

29. • In the liver, however, fructose enters by a
different pathway. The liver enzyme
fructokinase catalyzes the phosphorylation of
fructose at C-1 rather than C-6
• The fructose 1-phosphate is then cleaved to
glyceraldehyde and dihydroxyacetone
phosphate by fructose 1-phosphate aldolase

30. Galactose
• The conversion proceeds through a sugar-
nucleotide derivative, UDPgalactose, which is
formed when galactose 1-phosphate
displaces glucose 1-phosphate from UDP-
glucose.
• UDP-galactose is then converted by UDP-
glucose 4-epimerase to UDP-glucose, in a
reaction that involves oxidation of C-4 (pink)
by NAD, then reduction of C-4 by NADH; the
result is inversion of the configuration at C-4.
• The UDPglucose is recycled through another
round of the same reaction. The net effect of
this cycle is the conversion of galactose 1-
phosphate to glucose 1-phosphate; there is
no net production or consumption of UDP-
galactose or UDP-glucose.
Fig: Conversion of galactose to
glucose 1-phosphate.

31. Pasteur effect
• The inhibition of glycolysis by oxygen (aerobic condition)
is known as Pasteur effect.
• Discovered by Louis Pasteur while studying fermentation
in yeast.
• He observed that when anaerobic yeast cultures were
exposed to air, the utilization of glucose decreased by 7 fold.
• The levels of glycolytic intermediates from fructose 1,6
bisphosphate onward decrease while the earlier
intermediates accumulate
• This is due to inhibition of Phosphofructokinase
• The inhibitory effect of citrate and ATP on
phosphofructokinase explains the Pasteur effect

32. Crabtree effect
• The phenomenon of inhibition of oxygen consumption
by the addition of glucose to tissues having high
aerobic glycolysis is known as Crabtree effect.
• It is due to increased competition of glycolysis for
inorganic phosphate (Pi) and NAD+ which limits their
availability for phosphorylation and oxidation