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Understanding Glycolysis: Energy Harvesting from Glucose to Pyruvate

Glycolysis is a critical metabolic pathway that breaks down glucose to produce pyruvate, thereby harvesting energy. This process involves multiple enzymatic steps where glucose is split, resulting in two molecules of pyruvate. Key outcomes include the reduction of NAD+ to NADH and production of ATP through substrate-level phosphorylation. While some energy is captured as ATP, the majority remains in pyruvate, which enters the citric acid cycle for further degradation. This document explores the stages and chemical transformations involved in glycolysis.

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Understanding Glycolysis: Energy Harvesting from Glucose to Pyruvate

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  1. 6.7 Glycolysis • Glycolysis harvests chemical energy by oxidizing glucose to pyruvate • A single molecule of glucose is “cut in half” by enzymes through a series of steps to produce two molecules of pyruvate. • In the process, two molecules of NAD+ are reduced to two molecules of NADH • At the same time, two molecules of ATP are produced by substrate-level phosphorylation

  2. 6.7 Glycolysis • In substrate-level phosphorylation, an enzyme transfers a phosphate group from a substrate molecule to ADP… forming ATP • This ATP can be used immediately, but NADH must be transported to the electron transport chain to generate additional ATP

  3. 6.7 Glycolysis • MOST of the energy from Glucose is still in the pyruvate, and therefore pyruvate will move to the citric acid cycle to be further broken down.

  4. Glucose 2 ADP 2 NAD+ + 2 P 2 NADH ATP 2 + H+ 2 2 Pyruvate

  5. Enzyme Enzyme P ADP + ATP P P Substrate Product

  6. ENERGY INVESTMENT PHASE Glucose ATP Steps – A fuel molecule is energized, using ATP. Step 1 3 1 ADP Glucose-6-phosphate P 2 P Fructose-6-phosphate ATP 3 ADP P P Fructose-1,6-bisphosphate

  7. ENERGY INVESTMENT PHASE Glucose ATP Steps – A fuel molecule is energized, using ATP. Step 1 3 1 ADP Glucose-6-phosphate P 2 P Fructose-6-phosphate ATP 3 ADP P P Fructose-1,6-bisphosphate Step A six-carbon intermediate splits Into two three-carbon intermediates. 4 4 P P Glyceraldehyde-3- phosphate (G3P)

  8. Glyceraldehyde-3-phosphate (G3P) P P NAD+ NAD+ 5 5 Step A redox reaction generates NADH. 5 ENERGY PAYOFF PHASE P P NADH NADH  H+  H+ P P P P 1,3-Bisphosphoglycerate

  9. Glyceraldehyde-3-phosphate (G3P) P P NAD+ NAD+ 5 5 Step A redox reaction generates NADH. 5 ENERGY PAYOFF PHASE P P NADH NADH  H+  H+ P P P P 1,3-Bisphosphoglycerate ADP ADP 6 6 ATP ATP P P 3-Phosphoglycerate 7 7 Steps – ATP and pyruvate are produced. 6 9 P P 2-Phosphoglycerate 8 8 H2O H2O P P Phosphoenolpyruvate (PEP) ADP ADP 9 9 ATP ATP Pyruvate

  10. 6.8 Pyruvate is chemically groomed for the citric acid cycle • The pyruvate formed in glycolysis is transported to the mitochondria, where it is prepared for entry into the citric acid cycle • The first step is removal of a carboxyl group that forms CO2 • The second is oxidization of the two-carbon compound remaining • Finally, coenzyme A binds to the two-carbon fragment forming acetyl coenzyme A

  11.  H+ NAD+ NADH 2 CoA Acetyl coenzyme A Pyruvate 1 3 CO2 Coenzyme A

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