2. Introduction
Phases of the Glycolysis
Schematic pathway of the Glycolysis
Stepwise reactions of the Glycolysis
Fate of the Pyruvate
Energetics
Regulation
Conclusion
Bibliography
CONTENTS
3. The term ‘GLYCOLYSIS’ has originated from the Greek words, ‘glykys’ for
sugar and ‘lysis’ for splitting or breakdown.
Glycolysis is the sequence of 10 enzyme-catalyzed reactions, in which one
molecule of glucose is partially oxidized to form two molecules of Pyruvic acid.
It occurs in the cytoplasm of the cell and present in all living organism.
This pathway occurs aerobically as well as anaerobically and common pathway
for all the organism. In case of anaerobic organism, it includes formation of
Lactate from Pyruvate. In aerobic organism, glycolysis is the prelude to TCA
Cycle and ETC.
Glycolysis is the principal route for carbohydrate metabolism.
The scheme of glycolysis was given by Gustav Embden, Otto Meyerhof, and J.
Parnas, and is often referred as EMP Pathway.
INTRODUCTION
4. Glycolysis leads to breakdown of 6-C glucose into two molecules of 3-C pyruvate with the
enzyme catalyzed reactions that can be divided into 2 phases:- 1) Phase 1- Preparatory
Phase. 2) Phase 2- Payoff Phase.
PHASES OF THE GLYCOLYSIS
Preparatory Phase Payoff Phase
6. STEPWISE REACTIONS OF GLYCOLYSIS
Glucose Glucose-6-phosphate
Hexokinase/Glucokinase
ATP ADP+Pi
Phosphohexose
Isomerase
Fructose 6-phosphate
Fructose 1,6-
bisphosphate
Phosphofructokinase
ATP
ADP+
Pi
Glyceraldehyde 3-
Phosphate
Dihydroxyacetone
Phosphate
Triosephosphate Isomerase
Aldolase
7. STEPWISE REACTIONS OF GLYCOLYSIS
(2) x Glyceraldehyde 3-
Phosphate
(2) x 1,3-
bisphosphoglycerate
Glyceraldehyde 3-Phosphate
dehydrogenase
2 NAD+ 2 NADH
+ H+
(2) x 3-
phosphoglycerate
Phosphoglycerate kinase
2 x
ATP
2 x
ADP+Pi
(2) x 2-
phosphoglycerate
Mutase
(2) x
Phosphoenolpyruvate
H2O
(2) x Pyruvate
Enolase
Pyruvate kinase
2 x
ATP
2 x
ADP+Pi
8. After the formation of Pyruvate, there are two pathways based on the availability of
oxygen:-
Under anaerobic condition pyruvate is reduced to lactate by lactate dehydrogenase. It is
also reduced to Ethanol (along with CO2) by pyruvate decarboxylase and alcohol
dehydrogenase.
Under aerobic condition, pyruvate is transported to mitochondria and undergoes oxidative
decarboxylation by pyruvate dehydrogenase to form Acetyl-CoA, then oxidation to
CO2 in the TCA Cycle.
FATE OF THE PYRUVATE
9. STEP NO. REACTION CONSUMPTION OF
ATP
GAIN OF ATP
1 Glucose Glucose 6-phosphate 1 -
3 Fructose 6-phosphate Fructose 1,6-
phosphate
1 -
6 Glyceraldehyde 3-phosphate 1,3-
bisphosphoglycerate
- (2.5x2)=5
[by respiratory chain
oxidation of 2 NADH]
7 1,3-bisphosphoglycerate 3-
Phosphoglycerate
- (1x2)=2
[by substrate-level
phosphorylation]
10 Phosphoenolpyruvate Pyruvate - (1x2)=2
[by substrate-level
phosphorylation]
TOTAL 2 9
ENERGETICS
*Net gain of ATP = (9-2) = 7
10. Glycolysis is mainly regulated b:- i) Enzymatic regulation ii) Hormonal regulation.
i) Enzymatic regulation: Three enzymes regulates the glycolysis majorly. They are
Hexokinase/Glucokinase, Phosphofructokinase & Pyruvate kinase. Hexokinase is
allosterically inhibited by Fructose 6- phosphate whereas, Glucokinase is activated by
insulin and inhibited by glucagon. Similarly, Pyruvate kinase is also activated by insulin and
inhibited by glucagon.
ii) Hormonal regulation: Glycolysis is stimulated by insulin whereas, it is inhibited by
glucagon & epinephrine.
REGULATION
11. The overall reactions of Glycolysis can be summarized as:
Glucose + 2Pi + 2ADP + 2NAD+ 2Pyruvate + 2NADH + 2ATP + 2H+ + 2H2O
Thus the simultaneous reactions involved in Glycolysis are:
Glucose is oxidized to Pyruvate.
NAD+ is reduced to NADH.
ADP is phosphorylated to ATP.
CONCLUSION
12. HARPER’S ILLUSTRATED BIOCHEMISTRY(30TH EDTION)- Victor W. RODWELL,
David A. BENDER, Kathleen M. BOTHAM, Peter J. KENNELLY, P. Anthony WEIL, PAGE
NO 168-174
LEHNINGER PRINCIPLES OF BIOCHEMISTRY(4TH EDITION)- David L. Nelson,
Michael M. Cox. PAGE NO 522-533
IMAGES:
• SLIDE-4: https://images.app.goo.gl/7L5iiFFfEn1eARMx9
• SLIDE-5: https://images.app.goo.gl/HZ1eWoCrAm2AGQci9
• SLIDE-8: BIOLOGY- TEXTBOOK FOR CLASS 11- NCERT, PAGE NO:230-231
BIBLIOGRAPHY
