• At the end of this lecture, student will be able to

– Explain reaction involved in glycolysis

– Describe energetics of glycolysis

– Discuss the disorders associated with glycolysis


• Universal pathway in the living cells

• Elucidated in 1940 by Embden-Meyerhof and referred to as Embden- Meyerhof pathway (E.M, pathway)

• Defined as the sequence of reactions converting glucose to pyruvate or lactate, with the production of ATP

• Chemical formula: C6H12O6

Salient features

• Takes place in all cells of the body & enzymes of this pathway are present in the cytosol of the cell

• Occurs in the absence of oxygen (anaerobic) or in the presence of oxygen (aerobic)

• Lactate is the end product under anaerobic condition & in aerobic condition pyruvate, which is then oxidized to CO2 & H2O

• Major pathway for ATP synthesis in tissues lacking mitochondria e.g. erythrocytes, cornea, lens etc.

• Very essential for brain which is dependent on glucose for energy

• Central metabolic pathway with many of its intermediates providing branch point to other pathways. Thus, the intermediates are useful for the synthesis of amino acids and fat

Reactions of glycolysis: The pathway can be divided into 3 phases

1. Energy investment phase or priming stage

2. Splitting phase

3. Energy generation phase.

1. Energy investment phase

• Glucose is phosphorylated to G-6-P by hexokinase or glucokinase

• This is an irreversible reaction, dependent on ATP and Mg2+

• G-6-P is impermeable to the cell membrane, thus, G-6-P undergoes isomerization to give F-6-P in the presence of phosphohexose isomerase and Mg2+


• F-6-P is phosphorylated to fructose 1, 6 bisphosphate by phosphofructokinase

• This is an irreversible and a regulatory step in glycolysis


2. Splitting phase

• 6 C fructose 1, 6-bisphosphates split to two 3C compounds glyceraldehyde-3-P & di hydroxyacetone phosphate by the aldolase

• Enzyme phosphotriose isomerase catalyses the reversible interconversion of glyceraldehyde-3-P & dihydroxyacetone phosphate. Thus, 2 molecules of glyceraldehyde- 3-phosphate are obtained from one molecule of glucose


3. Energy generation phase

• Glyceraldehyde-3-phosphate dehydrogenase converts glyceraldehyde-3- P to 1,3-bisphosphoglycerate

• This step is important as it is involved in the formation of NADH + H+ & high energy compound 1,3-bisphosphoglycerate

• NADH passes through the ETC & 6 ATP are synthesized by oxidative phosphorylation

• Enzyme phosphoglycerate kinase acts on 1,3-bisphosphoglycerate resulting in the synthesis of ATP and formation of 3-phosphoglycerate. This is a good example of substrate Ievel phosphorylation and reaction is reversible

• 3-Phosphoglycerate is converted to 2- phosphoglycerate by phosphoglycerate mutase. This is an isomerization reaction

• High energy compound phosphoenol pyruvate is generated from 2-phosphoglycerate by enolase, requires Mg2+ or Mn2+

• Enzyme pyruvate kinase catalyses the transfer of high energy phosphate from phosphoenol pyruvate to ADP, leads to form of ATP and pyruvate. This step also is a substrate level phosphorylation & reaction is irreversible

• Glycolysis under aerobic condition produce pyruvate and under anaerobic condition produce lactate

• Conversion of pyruvate to lactate is by lactate dehydrogenase and NADH

Lactic acidosis

• Normal plasma concentration lactic acid is 4-15 mg/dl

• Elevation of lactic acid in the circulation may occur due to its increased production or decreased utilization of lactic acid

• Mild forms are associated with strenuous exercise, shock, respiratory diseases, cancers/low pyruvate dehydrogenase activity

• Severe forms are observed due to impairment/collapse of circulatory system which is often encountered in MI, pulmonary embolism, uncontrolled hemorrhage and severe shock, which may even lead to death

Energetics: Production of ATP

• Under anaerobic conditions, 2 ATP are synthesized while, under aerobic conditions, 8 or 6 ATP are synthesized depending on the shuttle pathway that operates.

Energetics: Production of ATP

Irreversible steps in glycolysis

• Three steps catalyzed by enzymes hexokinase (or glucokinase), phosphofructokinase and pyruvate kinase, are irreversible steps

Regulation of glycolysis

• Three enzymes namely hexokinase phosphofructokinase and pyruvate kinase, catalysing the irreversible reactions regulate glycolysis

Regulation of glycolysis


• Glycolysis also known as Embden-Meyerhof pathway

• Sequence of reactions converting glucose to pyruvate or lactate, with the production of ATP is known as glycolysis

• Glucose chemical formula is C6H12O6

• Glycolysis pathway is divided into 3 phases; Energy investment phase or priming stage, Splitting phase & Energy generation phase

• Elevation of lactic acid in the circulation is known as Lactic acidosis

• 8 ATP are synthesized in glycolysis

Also, Visit:

B. Pharma Notes | B. Pharma Notes | Study material Bachelor of Pharmacy pdf

B. Pharma Handwritten Notes

B. Pharma PDF Books

B. Pharma Lab Manual

D. Pharma Lab Manual

B. Pharma 8th Semester Previous Year Question Paper

D. Pharma Notes