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Glycolytic Pathway: Reactions, Stages & Enzymes

This detailed guide explores the glycolytic pathway, where glucose is converted to pyruvate, generating ATP and NADH along two stages comprising enzyme-catalyzed reactions. Learn about the preparatory and payoff stages, key enzymes like hexokinase and aldolase, and the formation of high-energy intermediates. Dive into the mechanism of each reaction and the role of ATP generation. Gain insight into how glycolysis efficiently breaks down glucose to produce energy for cells.

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Glycolytic Pathway: Reactions, Stages & Enzymes

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  1. 1. The Glycolytic Pathway 2. The Reactions of Glycolysis By: Mohammed Imran Anees Y.B.C.C.P Aurangabad Glycolysis

  2. Glycolysis Glucose is converted to pyruvate while generating two ATPs. 2 molecules of NAD+ are converted to 2 molecules of NADH. The oxidizing power of NAD+ must be recycled.

  3. There are 10 enzyme-catalyzed reactions considered to occur in two stages • Stage I (reactions 1-5): Preparatory stage where glucose is phosphorylated and cleaved to yield 2 molecules of glyceraldehyde-3-phosphate (GAP). Stage I uses 2 ATPs. • Stage II (reactions 6-10) Payoff stage where 2 GAPs converted to pyruvate and generation of 4 ATPs. Pathway Overview

  4. 1. Hexokinase (first ATP utilization) 2. Phosphoglucose Isomerase (PGI) 3. Phosphofructokinase -1 (PFK-1) (second ATP utilization) 4. Aldolase 5. Triose Phosphate Isomerase (TIM) The Reactions of GlycolysisStage I (Preparatory Stage)

  5. THE PREPARATORY PHASE Step 1 – Hexokinase

  6. Step 2 – Phosphoglucose Isomerase (PGI) [Phosphohexose isomerase] Phosphoglucose Isomerase catalyzes the conversion of G6P to F6P, the isomerization of an aldose to a ketose.

  7. The isomerization of an aldose to a ketose

  8. (C) Step 3 - Phosphofructokinase 1: Second ATP utilization

  9. Aldolase catalyzes cleavage of fructose-1,6-bisphosphate (FBP) in reaction 4 of glycolysis. • This forms two trioses • Glyceraldehyde-3-phosphate (GAP) • Dihydroxyacetone phosphate (DHAP). D. Step 4 - Aldolase

  10. Step 4 - Aldolase. Aldol cleavage of FBP to form two Trioses (GAP and DHAP) Note that the atom numbering system changes. Atoms 1, 2, and 3 of glucose become atoms 3,2, and 1 of DHAP. Atoms 4, 5, and 6 become atoms 1, 2, and 3 of GAP.

  11. (E) Step 5 - Triose Phosphate Isomerase (TIM) Only GAP continues along the glycolytic pathway.

  12. 6. Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH) first "High-energy" intermediate formation. • 7. Phosphoglycerate Kinase (PGK): First ATP Generation. • 8. PhosphoglycerateMutase (PGM). • 9. Enolase: second "High-energy" intermediate formation. • 10. Pyruvate Kinase (PK): Second ATP generation. Stage II - payoff phase

  13. (F) Step 6 - Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH): First “High-Energy” Intermediate Formation.

  14. (G). Step 7 - Phosphoglycerate Kinase (PGK): First ATP Generation.

  15. Mechanism of the PGK reaction.

  16. (H). Step 8 - Phosphoglycerate Mutase (PGM).

  17. (I) Step 9 - Enolase: Second “High-Energy” Intermediate Formation. (Dehydration reaction)

  18. (J) Step 10 - Pyruvate Kinase (PK) : Second ATP Generation.

  19. Thank you

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