Understanding Glycolysis and ATP Production

Key Concepts of Glycolysis

• Overview of Glycolysis: A metabolic pathway where glucose is converted to pyruvate, yielding ATP.

• ** ATP Production**: Produced through substrate-level phosphorylation, a rapid production method directly using glycolytic enzymes.

Substrate-Level Phosphorylation vs Oxidative Phosphorylation

• Substrate-Level Phosphorylation:

  • Involves transferring a phosphate group from a glycolytic intermediate to ADP.

  • Occurs in glycolysis and the citric acid cycle (TCA cycle).

  • Results in a net yield of 2 ATP from glycolysis directly.

• Oxidative Phosphorylation:

  • Involves removing electrons during glycolysis, pyruvate dehydrogenase complex reactions, and the citric acid cycle.

  • Electrons are transferred to NAD+ to form NADH and FAD to form FADH2.

  • Electrons are carried to the electron transport chain (ETC) leading to proton pumping, creating a proton gradient.

  • The final electron acceptor in ETC is oxygen, which is essential for generating ATP via chemiosmosis.

Detailed Pathway of Glycolysis

• Energy Investment Phase:

  • ATP is utilized initially to prepare glucose for breakdown into pyruvate.

  • Key Steps:

    • Glucose to Glucose-6-Phosphate: Catalyzed by hexokinase, this step uses one ATP.

      • Significance: Phosphorylation traps glucose inside the cell and increases its reactivity.

    • Glucose-6-Phosphate to Fructose-6-Phosphate: Rearrangement facilitated by phosphoglucose isomerase.

    • Fructose-6-Phosphate to Fructose-1,6-Bisphosphate: Catalyzed by phosphofructokinase, another ATP is consumed leading to a highly unstable intermediate.

• Cleavage Phase:

  • From fructose-1,6-bisphosphate, the molecule splits into two 3-carbon molecules: dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P).

  • The continuation of glycolysis from this point involves processing both 3-carbon molecules, and everything is considered in terms of these two products henceforth.

Enzymatic Functions in Glycolysis

• Dehydrogenase Role:

  • Enzymes that catalyze reduction reactions by removing hydrogen atoms (2 electrons and 2 protons), often linked to NAD+ reduction to NADH.

• Kinase Function:

  • Kinases, such as hexokinase and phosphofructokinase, are responsible for transferring phosphate groups, essential for the regulation and progression of glycolysis.

Key Points for Exam Preparation

• Comparative Knowledge: Be able to compare substrate-level and oxidative phosphorylation.

• Recognizing Key Pathway Steps: Understand critical steps where ATP is invested and produced.

• Enzymes Involved: Familiarize with names and functions of enzymes such as hexokinase, phosphofructokinase, and dehydrogenases.

• Products of Glycolysis: Know that glycolysis results in pyruvate, and recognize that the energy yield increases significantly with aerobic respiration compared to anaerobic processes.