Glycolysis is the process in which one mole of glucose is partially oxidized into two mole of pyruvate in a series of enzyme-catalyzed reactions. it is also known as Embden-Meyerhof-Parnas pathway (EMP pathway).

1. St. Xavier’s College, Mahuadanr (Plant Physiology)
Dr. Emasushan Minj (Assistant Professor) 1
GLYCOLYSIS
 All life processes require energy. Much of the food obtained by autotrophic and heterotrophic nutrition is used as a
source of this energy. The energy rich compounds are broken down to release energy by the process of respiration.
 Respiration is a process by which the energy of the food is made available to the cells.
 Glycolysis (from the Greek glykys, meaning sweet and lysis, meaning splitting) also known as Embden-Meyerhof-
Parnas pathway.
 It is the process in which one mole of glucose is partially oxidized into two mole of pyruvate in a series of enzyme-
catalyzed reactions.
 Glycolysis occurs in the cytosol of all cells.
 It is a unique pathway occurs in both aerobic and anaerobic conditions.
 Glucose is the most common respiratory substrate.
 Photosynthesis is 10 times faster than respiration.
 About 50% of sugar formed in photosynthesis is used in respiration.
 Cellular respiration is essentially a catabolic process, involves biological oxidation of organic molecules and results in
the release of the energy in the form of ATP.
 ATP is an instant source of energy which is mobile and transports chemical energy within the cell. The hydrolysis of
ATP releases energy. Since ATP is found in all living cells, it is called universal energy carrier or “energy currency”
of cells.
 A respiratory substrate is a “substance which is oxidized to yield the energy necessary for cell maintenance and growth”.
These, include carbohydrates, fats and proteins.
Types of respiration:
(a) Aerobic respiration.
It takes place in the presence of oxygen. Complete oxidation of the substrate results in the formation of CO2 and water
accompanied by the release of energy e.g. in germinating seeds, in fruits and among many microorganisms e.g. yeasts
and bacteria.
C6H12O6 + 6O2 ® 6CO2 + 6H2O + energy (Glucose) (686 kcal)
In most forms of life, respiration occurs aerobically.
(b) Anaerobic respiration.
It takes place in the absence of oxygen and results in incomplete degradation of the substrate. CO2 and organic
compounds like ethyl alcohol, lactic acid etc., are produced accompanied by the release of some energy, water is not a
product of this reaction.
C6H12O6 ® 2C2H5OH + 2CO2 + energy

2. St. Xavier’s College, Mahuadanr (Plant Physiology)
Dr. Emasushan Minj (Assistant Professor) 2

3. St. Xavier’s College, Mahuadanr (Plant Physiology)
Dr. Emasushan Minj (Assistant Professor) 3

4. St. Xavier’s College, Mahuadanr (Plant Physiology)
Dr. Emasushan Minj (Assistant Professor) 4
Step 1(Phosphorylation):
 Glucose is phosphorylated by ATP to form a glucose 6-phosphate. This reaction is irreversible catalyzed by
hexokinase. In animal this enzyme is called glucokinase present in liver and β-cells of the pancreas.
Step 2(Isomerization):
 A reversible rearrangement of the chemical structure (isomerization) and form ketose from aldose sugar. The
isomerization of glucose 6-phosphat to fructose 6-phosphate is catalyzed by phosphoglucoisomerase.
Step 3(Phosphorylation):
 Fructose 6-phosphate is phosphorylated by ATP to fructose 1,6-diphosphate. This irreversible reaction is
catalyzed by an allosteric enzyme phosphofructokinase.
Step 4(Cleavage):
 The fructose 1,6-diphosphate is cleaved to produce two three-carbon molecules- glyceraldehydes 3-phosphate
(G3P) and dihydroxyacetone phosphate (DHAP). This reaction is catalyzed by enzyme aldolase.
Step 5(Isomerization):
 Only one of the two triose phosphates formed by aldolase- glyceralde 3-phosphate can be directly degraded in
the subsequent reaction step of glycolysis. However, the other product, dihydroxyacetone phosphate, is rapidly
and reversibly converted into glyceraldehyde 3-phosphate by the enzyme triose phosphate isomerase.
Step 6:
 The two molecules of glyceraldehydes 3-phosphate are oxidized and converted into 1,3-diphosphoglycerate
catalyzed by glyceraldehydes 3-phosphate dehydrogenase.
Step 7:
 In this step, high-energy phosphate group is transferred from 1,3-diphosphoglycerate to ADP. Formation of
ADP to ATP by direct transfer of phosphate group from a ‘high-energy’ compound is termed as substrate-level-
phosphorylation.
Step 8:
 The remaining phosphate ester linkage in 3-phosphoglycerate, which has a relatively low free energy of
hydrolysis, is moved from carbon to carbon 2-phosphoglycerate.
Step 9:
 The removal of water from 2-phosphoglycerate creates a high-energy enol phosphate linkage. The enzyme
catalyzing this step, enolase, is inhibited by fluoride.
Step 10:
 The transfer of the high-energy phosphate group that was generated in step 9 to ADP forms ATP. This step in
glycolysis is the irreversible transfer of the phosphoryl group from phosphoenolpyruvate to ADP is catalyzed by
pyruvate kinase. Pyruvate kinase requires K+
and either Mg+
or Mn+
.
Net reaction: Glucose + 2 NAD+
= 2ADP + 2HPO4
2-
→ 2 PYRUVATE + 2NADH +2ATP +H2O

5. St. Xavier’s College, Mahuadanr (Plant Physiology)
Dr. Emasushan Minj (Assistant Professor) 5
Energetic of Glycolysis