Glycolysis Pathway Made Simple !! Biochemistry Lecture on Glycolysis

Glycolysis: A Detailed Breakdown

Key Concepts:

• Glycolysis: Breakdown of glucose to produce energy.
• ATP (Adenosine Triphosphate): Energy currency of the cell.
• NADH (Nicotinamide Adenine Dinucleotide): Electron carrier used in energy production.
• Pyruvate: A three-carbon compound, the end product of glycolysis.
• Kinase: Enzyme that catalyzes phosphorylation reactions (transfer of phosphate groups).
• Isomerase: Enzyme that catalyzes the conversion of a molecule to its isomer.
• Dehydrogenase: Enzyme that catalyzes the removal of hydrogen atoms.
• Mutase: Enzyme that catalyzes the shifting of a functional group from one position to another within the same molecule.
• Phosphorylation: Addition of a phosphate group to a molecule.

Overview of Glycolysis

Glycolysis is a metabolic pathway that occurs in the cytosol of cells. It involves the systematic breakdown of a six-carbon glucose molecule into two molecules of a three-carbon compound called pyruvate. This process releases energy in the form of ATP and NADH. The pyruvate produced can then be used in other energy-producing pathways to generate more energy.

Two Phases of Glycolysis

Glycolysis is divided into two phases:

1. Energy Investment Phase: Glucose is converted into two molecules of glyceraldehyde-3-phosphate (G3P). This phase requires energy input in the form of ATP.
2. Energy Payoff Phase: Glyceraldehyde-3-phosphate is converted into pyruvate, producing ATP and NADH.

Detailed Reactions of Glycolysis

1. Glucose to Glucose-6-Phosphate:

   • Enzyme: Hexokinase
   • Reaction: Hexokinase transfers a phosphate group from ATP to glucose, forming glucose-6-phosphate.
   • ATP is converted to ADP.
   • Hexo refers to the six-carbon glucose molecule. Kinases catalyze phosphorylation reactions.

2. Glucose-6-Phosphate to Fructose-6-Phosphate:

   • Enzyme: Isomerase
   • Reaction: Glucose-6-phosphate is converted to its isomer, fructose-6-phosphate.
   • This is a rearrangement reaction.

3. Fructose-6-Phosphate to Fructose-1,6-Bisphosphate:

   • Enzyme: Phosphofructokinase
   • Reaction: Phosphofructokinase adds another phosphate group to fructose-6-phosphate, forming fructose-1,6-bisphosphate.
   • ATP is converted to ADP.
   • Another ATP molecule is utilized.

4. Fructose-1,6-Bisphosphate to Glyceraldehyde-3-Phosphate and Dihydroxyacetone Phosphate:

   • Enzyme: Aldolase
   • Reaction: Fructose-1,6-bisphosphate is split into two three-carbon molecules: glyceraldehyde-3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP).

5. Dihydroxyacetone Phosphate to Glyceraldehyde-3-Phosphate:

   • Enzyme: Isomerase
   • Reaction: Dihydroxyacetone phosphate is converted to glyceraldehyde-3-phosphate.
   • Since G3P is used in the subsequent steps, the equilibrium favors G3P formation.
   • Every molecule of glucose is split into two molecules, so every reaction of the second phase happens twice and produces twice the products.

The Energy Payoff Phase (Reactions occur twice per glucose molecule):

6. Glyceraldehyde-3-Phosphate to 1,3-Bisphosphoglycerate:

   • Enzyme: Glyceraldehyde-3-phosphate dehydrogenase
   • Reaction: Glyceraldehyde-3-phosphate is converted to 1,3-bisphosphoglycerate.
   • NAD+ is reduced to NADH.
   • Inorganic phosphate is utilized.
   • NADH is later used in the electron transport chain to produce more energy.

7. 1,3-Bisphosphoglycerate to 3-Phosphoglycerate:

   • Enzyme: Phosphoglycerate kinase
   • Reaction: Phosphoglycerate kinase transfers a phosphate group from 1,3-bisphosphoglycerate to ADP, forming ATP and 3-phosphoglycerate.
   • ATP is generated.

8. 3-Phosphoglycerate to 2-Phosphoglycerate:

   • Enzyme: Phosphoglycerate mutase
   • Reaction: 3-Phosphoglycerate is converted to 2-phosphoglycerate.
   • This is a rearrangement reaction.

9. 2-Phosphoglycerate to Phosphoenolpyruvate (PEP):

   • Enzyme: Enolase
   • Reaction: 2-Phosphoglycerate is converted to phosphoenolpyruvate.
   • Magnesium ions are also utilized in this reaction.

10. Phosphoenolpyruvate to Pyruvate:

    • Enzyme: Pyruvate kinase
    • Reaction: Pyruvate kinase transfers a phosphate group from phosphoenolpyruvate to ADP, forming ATP and pyruvate.
    • ATP is generated.

Net Reaction of Glycolysis

• 1 Glucose → 2 Pyruvate
• Net: 2 ATP (4 ATP produced - 2 ATP used)
• 2 Inorganic Phosphate utilized
• 2 NAD+ → 2 NADH

Conclusion

Glycolysis is a fundamental metabolic pathway that breaks down glucose to produce energy. It involves a series of enzymatic reactions that occur in two phases: an energy investment phase and an energy payoff phase. The end products of glycolysis, pyruvate, ATP, and NADH, are crucial for further energy production in the cell.