Carbohydrate Metabolism Overview
Citric Acid Cycle Overview Metabolism &
Energy Summary
 Elmhurst College
Glycolysis Summary Pyruvic Acid - Crossroads  Chemistry Department
Glycolysis Reactions Glycogenesis / Glycogenolysis / Gluconeogenesis  Virtual ChemBook

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Pyruvic Acid - Cross Roads Compound

Introduction to Pyruvic Acid:

Depending upon the conditions and the organism under consideration, a variety of metabolic fates await pyruvic acid.

1) Acetyl CoA: If the conditions are aerobic, pyruvic acid is converted into acetyl CoA for entry into the citric acid cycle - see diagram on the left. This will be considered in detail in a following page.

2) Gluconeogenesis: Pyruvic acid can be converted back to glucose or glycogen by the process of gluconeogenesis to be described later.

3) Alanine: Pyruvic acid can be converted into the amino acid alanine by the process of transamination to be described in a later chapter.

Glycolysis - with white background for printing

Link to: Interactive Fate of Pyruvic Acid (move cursor over arrows)
Jim Hardy, Professor of Chemistry, The University of Akron.

4) Anaerobic Synthesis of Lactic Acid:

If conditions are anaerobic, pyruvic acid is converted into lactic acid. The purpose of this reaction is to convert NADH from Step 5 back into NAD+. This allows glycolysis to continue to produce ATP (and energy) at steps 6 and 9 in the absence of oxygen. This occurs under strenuous exercise conditions in the muscles. The vigorous exercise soon strips the cells of available ATP (energy). Oxygen cannot be resupplied to the cells at a fast enough rate, therefore, an oxygen debt or anaerobic conditions result. The reaction is shown on the left:

Glycolysis - with white background for printing

5) Fermentation - Ethanol:

Yeast and several other microorganisms undergo glycolysis or fermentation to produce ethanol from sugars. This is the process to make wine, beer, and other alcoholic products from grains and fruits.

The reactions of glycolysis are identical to those described up to the production of pyruvic acid. The difference is in the fate of pyruvic acid. In fermentation, pyruvic acid is converted first to ethanal (acetaldehyde) and then to ethanol. Again, the NADH from Step 5 is converted back to NAD+ in this process.

The reaction sequence is shown on the left.