Lactic acid is formed in glycolysis when pyruvate, the end product of glycolysis, is reduced by NADH in the absence of sufficient oxygen.
Here's a breakdown of the process:
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Glycolysis and Pyruvate Production: Glycolysis is the metabolic pathway that breaks down glucose into pyruvate. This process occurs in the cytoplasm of cells and generates ATP (energy) and NADH.
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Anaerobic Conditions (Lack of Oxygen): Under normal aerobic conditions, pyruvate enters the mitochondria to undergo further oxidation in the Krebs cycle (citric acid cycle) and oxidative phosphorylation. However, when oxygen is limited (anaerobic conditions), the electron transport chain slows down, and NADH accumulates.
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Reduction of Pyruvate to Lactate: To regenerate NAD+ needed for glycolysis to continue, pyruvate is reduced to lactate (lactic acid) by the enzyme lactate dehydrogenase (LDH). NADH donates its electrons to pyruvate, converting it to lactate and regenerating NAD+.
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Equation:
Pyruvate + NADH + H+ <--> Lactate + NAD+ -
Significance: This process allows glycolysis to continue producing ATP even when oxygen is scarce. The regeneration of NAD+ is crucial because NAD+ is a necessary coenzyme for an earlier step in glycolysis.
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Fate of Lactate: Lactate can be converted back to pyruvate in the liver through the Cori cycle, when oxygen becomes available again.
Therefore, the critical step in lactic acid formation is the reduction of pyruvate by NADH, catalyzed by lactate dehydrogenase, under anaerobic conditions to regenerate NAD+ for glycolysis to continue. Two molecules of lactate are produced for every two molecules of pyruvate.
