Introduction to Glycolysis for basic biochemistry

1. Glycolysis

2. Lesson Learning Outcome
Upon completion of this lecture,
should be able to:
• understand the glycolytic pathway
• fates of pyruvate
students

4. Cellular
Respiration
• Is a set of metabolic reactions and
processes that take place in the cells of
organisms to convert biochemical
energy from nutrients into
adenosine triphosphate (ATP), and then
release waste product.
• The reactions involved in respiration
are catabolic reactions, which break
large molecules into smaller ones,
releasing energy in the process.
• Cellular respiration
is considered
an exothermic redox reaction which
releases heat.

5. Overall cellular respiration

7. The Glycolytic Pathway
Glucose is converted to two pyruvate

8. Glycolysis

10. Glycolysis
• In cytoplasm, an anaerobic process which generates
ATP, NAPH and pyruvate
• Glycolysis: a series of 10 enzyme-catalyzed reactions
by which glucose is oxidized to two molecules of
pyruvate
– there is net conversion of 2ADP to 2ATP
C6 H1 2 O6
Glucose
glycolysis
O
2 CH3 CCOO-
Pyruvate
+ 2 H+
+ 2 ADP + 2 Pi + 2 ATP
C6 H1 2 O6
Glucose
O
2 CH3 CCOO-
Pyruvate

11. Fates of Pyruvate
• Pyruvate is most commonly metabolized in one of
three ways, depending on the type of organism and
the presence or absence of O2
O
CH3 CCOO-
Pyruvate
OH
CH3 CHCOO-
Lactate
CH3 CH2 OH + CO2
Ethanol
3 CO2 + 2 H2 O
aerobic conditions
plants and animals
anaerobic conditions
contracting muscle
anaerobic conditions
fermentation in yeast

12. Reactions of glycolysis
• Reaction 1: phosphorylation of -D-glucose to
give glucose-6-phosphate
OH
OH
HO
HO
CH2 OH
O
+ -O- P-O- P-O- AM P
O- O-
ATP
-D-Glucose
hexokinase
Mg 2 +
OH
HO
HO
CH2 OPO3
2 -
O
OH
-D-Glucose-6-phosphate
+
O
-O- P-O- AM P
O-
ADP
O O

13. – this reaction is driven by the free energy of hydrolysis
of ATP
– These two reaction are coupled, so the overall
reaction is the sum of the two and is exergonic
– The enzyme that catalyzes this reaction is hexokinase
– Glucose-6-phosphate inhibits hexokinase – feedback
inhibition

14. • Reaction 2: isomerization of glucose-6-phosphate to
fructose-6-phosphate
-D-Glu
• The enzyme that catalyzes this reaction is
glucosephosphate isomerase
• The aldehyde group at C1 is reduced to hydroxyl, and the
C2-hydroxyl is oxidized to give the ketone group of fructose-
6-phosphate
2 3
6
CH OPO 2 -
OH
HO
HO
CH2 OPO3
O
2 -
phosphogluco-
isomerase
1
2
6

16. • Reaction 3: phosphorylation of fructose-6-phosphate
1
CH2 OH
OH
H
O
H HO
-D-Fructose-6-phosphate
6
CH2 OPO3
2 -
HO H
+ ATP
phospho-
fructokinase
Mg 2 +
2 3 1
CH2 OPO3
2 -
O
OH
H
H HO
6
CH OPO
HO H
-D-Fructose-1,6-bisphosphate
• The phosphorylation of fructose-6-phosphate is highly
exergonic and irreversible – enzyme responsible is
phosphofructokinase
2 -
+ ADP

17. • Reaction 4: cleavage of fructose-1,6-bisphosphate to
two triose phosphates by enzyme aldolase
2
C=O
CH OPO3
HO H
H OH
H OH
CH2 OP
Fruct
2-
aldolase
CH2 OPO3
2 -
C=O
CH2OH
Dihydr

18. • Reaction 5: isomerization of triose phosphates
– catalyzed by triosephosphate isomerase
– reaction involves two successive keto-enol
tautomerizations
– only the D enantiomer of glyceraldehyde 3-
phosphate is formed
CH2 OH
C= O
CH2 OPO3
2 -
Dihydroxyacetone
phosphate
CHO
H C OH
CH2 OPO3
2 -
D-Glyceraldehyde
3-phosphate
CHOH
C-OH
CH2 OPO3
2 -
An enediol
intermediate

19. • Reaction 6: oxidation of the -CHO group of D-
glyceraldehyde-3-phosphate
– the -CHO group is oxidized to a carboxyl group
– the oxidizing agent, NAD+, is reduced to NADH
G - C - H +
A t w o - e l e c t r o n o x i d a t i o n
O
H 2 O G - C - O H
O
2 H + 2 e -
H +
2 e - N A D H
A t w o - e l e c t r o n r e d u c t i o n
+
+
+
N A D + +
O
G - C - H + H 2 O + N A D +
O
G - C - O H H +
+

20. ◾the overall reaction involves an exergonic oxidation
and an endergonic phosphorylation
◾the overall reaction is slightly endergonic
Go' = +49.3 kJ•mol -1
Go' = -43.1 kJ•mol -1
oxidation:
phosphorylation:
O
C-O-
O O
C-H to C-O-
O O
O
C-H to
to C-O- P-O-
O-
O O
C-O- P-O-
O-
Go' = +6.2 kJ•mol -1

21. • Reaction 7: transfer of a phosphate group from 1,3-
bisphosphoglycerate to ADP
– this reaction is called substrate-level
phosphorylation
+
1,3-Bisphospho-
glycerate
COO-
H C OH
CH2 OPO3
2 -
3-Phosphoglycerate
CH OPO
2 3
2 -
O
C-OPO3
2 -
H C OH
+
O
-O- P-O-AMP
O-
ADP
phospho-
glycerate kinase
Mg2+
-O- P-O- P-O-AMP
O O
O- O-
ATP

22. the sum of the endergonic
– this reaction is
phosphorylation of ADP and the exergonic
hydrolysis of the mixed phosphate anhydride
phosphorylation:
Go' = -49.3 kJ•mol -1
Go' = +0.5 kJ•mol -1
O
C-O-
O O
C-O-P-O-
O-
ADP + Pi
hydrolysis:
Go' = -18.8 kJ•mol -1
+ Pi
ATP + H2 O
O O
C-O- P-O-
O-
+ ADP + Pi
O
C-O- + ATP
+ H2 O

23. • Reaction 8: isomerization of 3-phosphoglycerate to
2-phosphoglycerate
COO-
H C OH
CH2 OPO3
2 -
3-Phosphoglycerate
COO-
H C OPO3
2 -
CH2 OH
2-Phosphoglycerate
phosphoglycerate
mutase

24. • Reaction 9: dehydration of 2-phosphoglycerate
3
COO-
H C
OP
O CH2
OH
2-Phosp
2-
COO-
C
enolase
Mg2+

25. • Reaction 10: phosphate transfer to ADP
stage 1: transfer of the phosphate group
COO-
C OPO
CH2
3
2 -
Phosphoenol-
pyruvate
+
-O- P-O- P-O-AMP
O- O-
ATP
COO-
C-OH
CH2
Enol of
pyruvate
O
-O- P-O-AMP
O-
ADP
+
pyruvate
kinase
Mg2+
O O

26. Stage 2: enolization to pyruvate
COO-
C-OH
CH2
Enol of pyruvate
COO-
C= O
CH3
Pyruvate

28. Glycolysis
• Summing these 10 reactions gives the net equation
for glycolysis
C6H12O6
Glucose
+ 2NAD+ + 2HPO4
2- + 2ADP glycolysis
O
2CH3CCOO-
Pyruvate
+ 2NADH+ 2A
TP + 2H2O+ 2H+

29. Energetics of Glycolysis
• Three reactions exhibit particularly large
decreases in free energy; the enzymes that
catalyze these reactions are sites of allosteric
control
– hexokinase
– phosphofructokinase
– pyruvate kinase

30. • Fructose is phosphorylated by fructokinase (liver) or
hexokinase (adipose) on the 1 or 6 positions resp.
• Fructose-6-phosphate is an intermediate of
glycolysis.
• Fructose-1-phosphate is acted upon by an aldolase-
like enzyme that gives DHAP (dihydroxyacetone
phosphate) and glyceraldehyde.
• DHAP is a glycolysis intermediate and glyceraldehyde
can be phosphorylated to glyceraldehyde-3-P.
• Glycerol is phosphorylated to G-3-P which is then
converted to glyceraldehyde 3 phosphate.

31. • Galactose has a slightly complicated multi-step
pathway for conversion to glucose-1-phosphate.
• gal gal-1-P UDP-gal UDP-glc glc-1-P.
• If this pathway is disrupted because of defect in one
or more enzymes involved in the conversion of gal to
glc-1-P, then galactose accumulates in the blood and
the subject suffers from galactosemia which is a
genetic disorder, an inborn error of metabolism.

33. Reactions of Pyruvate
• Pyruvate does not accumulate in cells, but
rather undergoes one of three enzyme-
catalyzed reactions, depending of the type of
cell and its state of oxygenation
– reduction to lactate
– reduction to ethanol
– oxidation and decarboxylation to acetyl-CoA

34. Lactate Fermentation
⦿In vertebrates 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
O
CH CCOO- + NADH + H+
3
Pyruvate
OH
CH3 CHCOO- + NAD+
Lactate
lactate
dehydrogenase

35. Pyruvate to Lactate
 while lactate fermentation allows glycolysis to
continue, it increases the concentration of lactate
and also of H+ in muscle tissue
 when blood lactate reaches about 0.4 mg/100
mL, muscle tissue becomes almost completely
exhausted
C6H12O6
Gluco
OH
lactate
fermentation

36. Pyruvate to Ethanol
• Yeasts and several other organisms regenerate NAD+
by this two-step pathway;
decarboxylation of pyruvate to acetaldehyde
3
P y r u v a t e
O
p y r u v a t e
d e c a r b o x y l a s e
O
C H C C O O - + H +
3
O
C H C H + N A D H +
reduction of acetaldehyde to ethanol
alcohol
H +
A ce ta lde hy de
de hy dro g e na s e
C H 3 C H 2 O H +
E t h a n o l
N A D +

37. Pyruvate to Acetyl-CoA
• Under aerobic conditions, pyruvate undergoes
oxidative decarboxylation
– the carboxylate group is converted to CO2
– the remaining two carbons are converted to the
acetyl group of acetyl-CoA
3
P y ru v a t e O
C H 3 C S C o A +
A c e t y l - C o A
C O 2 + N A D H
o x i d a t i v e
d e c a r b o x y l a t i o n
O
C H C C O O - + N A D + + C o A S H

39. End of lecture