Glycolysis is the breakdown of glucose into pyruvate. It occurs in 10 steps with 2 ATP molecules invested at the start and a net production of 2 ATP and 2 NADH. It is an important pathway as it is common to both aerobic and anaerobic respiration and generates precursors for biosynthesis. Key regulatory enzymes include hexokinase, phosphofructokinase, and pyruvate kinase which are inhibited when energy levels are high.

1. Glycolysis
Glycolysis
Presented by Agrani Paudel

2. Glycolysis
 Glyco- glucose; lysis – breakdown
 1 mole of 6-carbon glucose is broken
down into 2 moles of 3-carbon pyruvate
by 10 enzyme-catalyzed sequential
reactions.
 Energy as ATP and NADH (Nicotinamide
Adenine Dinucleotide).

3. Glycolysis (Embden Meyerhof Parnas Pathway;
EMP)
• Why an important path?
• common step for both aerobic and anaerobic respiration
• generate several biosynthetic precursors as 3 –phosphoglycerate;
(phosphoketolase pathway), Glyceraldehyde 3-phosphate (HMP);
pyruvate
• Product of other metabolism also ends in pyruvate or some product
of glycolysis
• glucose is the only fuel that brain uses under non starvation condition
and the only fuel red blood cells can use at all

4. Glycolysis
location : cytoplasm
Various enzymes required are in
cytosol and nearly all the enzymes
require Mg++
Glut 2 – liver , kidney
glut 4 – muscle, fat

5. Glycolysis – Can be divided into two phases
• FIRST PHASE: Preparatory phase
• Investment of 2 ATP molecules to
activate glucose molecule and
prepare for its cleavage
• use energy in form of ATP.

6. Glycolysis – Can be divided into two phases
• SECOND PHASE: Pay off
phase
• Glyceraldehyde-3-
Phosphate is converted
into pyruvate.
• In this phase energy is
produced in the form of
ATP and NADH

7. Step 1- Phosphorylation of glucose
• Glucose into Glucose-6-Phosphate
(G-6-P)
• Enzyme- HEXOKINASE
• transfer of phosphate from the
ATP(1st ATP utilized)

8. Step 2- Isomerization of Glucose-6-phosphate
• Glucose 6-phosphate to fructose 6-phosphate
• reversibly isomerized
• Enzyme- phosphohexose isomerase
• involves a shift of the carbonyl oxygen from C1 to
C2, thus converting an aldose into a ketose.

9. Step 3- Phosphorylation of fructose-6-phosphate
• F-6-P into Fructose 1,6- bisphosphate
• enzyme -phospho-fructokinase
• transferring a phosphate molecule from
another ATP to form an ADP (second ATP is
utilized).

10. Step 4- Cleavage of fructose 1, 6-diphosphate
• F1,6-Bis P into : ‘GLYCERALDEHYDE 3-
PHOSPHATE’(aldose) and ‘DIHYDROXYACETONE
PHOSPHATE’ (ketose); 3-carbon molecules
• Enzyme- ALDOLASE
• The remaining steps in glycolysis involve
three-carbon units, rather than six
carbon units.

11. Step 5- Isomerization of dihydroxyacetone phosphate
• dihydroxyacetone phosphate isomerized
into glyceraldehyde 3-phosphate
• enzyme -ISOMERASE
• Also, one molecule of Glucose gives two
molecules so every reaction occurs twice
and produce twice amount of products.

12. Step 6- Oxidative Phosphorylation of Glyceraldehyde 3-
phosphate
• G-3-P into 1,3- BISPHOSPHO GLYCERATE
• Enzyme-GLYCERALDEHYDE-3-PHOSPHATE
DEHYDROGENASE.
• addition of a phosphate group in the first position
of the G-3-P by a catalyzing Required: A co-
enzyme, NAD (Nicotinamide Adenine
Dinucleotide) which is reduced into NADH
• requires an inorganic phosphate group.
• two NADH are generated in this step.
(2)
(2)
(2)
(2)
(2)
(2)

13. Step 7- Transfer of phosphate from 1, 3-diphosphoglycerate
to ADP
• 1,3-bisphospho glycerate - 3-
PHOSPHOGLYCERATE
• enzyme -PHOSPHO GLYCERATE KINASE
• Here an ADP is converted to generate an ATP.
• Since two moles of 1, 3-bisphosphoglycerate
are formed from one mole of glucose, two
ATPs (substrate level phosphorylation)
(2) (2) (2) (2)

14. Step 8- Isomerization of 3-phosphoglycerate
• 3-phosphoglycerate into 2-
PHOSPHOGLYCERATE, simple
rearrangement reaction
• Enzyme -PHOSPHOGYCERATE MUTASE
• This is a reversible isomerization reaction.
(2) (2)

15. Step 9- Dehydration 2-phosphoglycerate
• 2-phosphoglycerate dehydrated to
phosphoenolpyruvate.
• enzyme -enolase (phosphopyruvate
hydratase)
• irreversible reaction ;two moles of water
are lost.
• MAGNESIUM ION.
(2)
(2)
(2)

16. Step 10- Transfer of phosphate from
phosphoenolpyruvate
• second energy-generating
• Phosphonenol pyruvate into PYRUVATE
• enzyme -PYRUVATE KINASE.
• enzyme catalyzes the transfer of a phosphoryl
group from phosphoenolpyruvate to ADP, thus
forming ATP.(substrate level phosphorylation)
(2)
(2) (2)
(2)

17. FIRST PHASE:
Energy is consumed -2ATP
SECOND PHASE:
Energy is produced -4ATP
Net reaction: C6H12O6 (Glucose) + 2ADP + 2Pi +
2NAD+ → 2C3H4O3 (Pyruvate) + 2H2O + 2ATP +
2NADH + 2H+
Glucose is oxidized into pyruvate.
NAD+ is reduced to NADH.
ADP is phosphorylated into ATP.

18. Fates of Pyruvate
•In conditions where
the oxygen is
insufficient, like in
the skeletal muscle
cells, the pyruvate
cannot be oxidized
due to lack of
oxygen.
•In some
microbes like
brewer’s yeast,
the pyruvate
formed from
glucose is
converted
anaerobically into
ethanol and CO2.

19. Fates of Pyruvate

20. Regulation of Glycolysis
• In metabolic pathways, the enzymes catalyzing essentially irreversible
reactions are potential sites of control
• Three irreversible kinase reactions primarily drive glycolysis forward
• Hexokinase Or Glucokinase
• Phosphofructokinase
• Pyruvate kinase
• Each of them serves as a control site

21. Hexokinase
• Phosphorylation of glucose
• Glucose 6-phosphate
• High concentration of this
molecule signal that the cell no
longer requires glucose for
energy and the glucose will be
left in the blood (hexokinase is
inhibited)

22. Phosphofructokinase
• rate limiting for glycolysis
• An allosteric regulatory enzyme
• Inhibitors: ATP and citrate
• Both indicate high energy availability
• Activators: ADP,AMP, low energy
• Fructose 2,6 bisphosphate is very
important regulator

23. Pyruvate kinase
• Inhibitors: ATP; acetyl coA and fatty
acids(alternative fuels for TCA cycle)
• Activator: fructose 1,6- bisphosphate( “feed-
forward”)
• Phosphorylation by glucagon (inactive form)
and dephosphorylation (active form) by insulin
under hormone control