Glycolysis Overview

BioFiles 2007, 2.6, 4.

BioFiles 2007, 2.6, 4.

Carbohydrates synthesized during photosynthesis act as the main storage molecules of solar energy. When ingested, complex carbohydrates are enzymatically hydrolyzed to monosaccharides, such as starch to D(+)-glucose.

The catabolism of glucose is the primary energy source for shortterm requirements and begins with the Embden-Meyerhoff-Pathway as illustrated in Figure 1. D(+)-Glucose (1) is phosphorylated in the first reaction with ATP to give glucose-6-phosphate (2).



Figure 1. Embden-Meyerhoff-Pathway


The isomerization of glucose-6-phosphate (2) in the second reaction to fructose-6-phosphate (3) occurs via ring-opening and subsequent keto-enol-tautomerization.

The third reaction is another phosphorylation with ATP, whereby fructose-6-phosphate (3) is converted to fructose-1,6-bisphosphate (4).

A key branching reaction is the fourth reaction: a ring-opening reaction of fructose-1,6-bisphosphate (4), which is cleaved in a retro-aldol reaction into D-glyceraldehyde-3-phosphate (5), and dihydroxyacetone phosphate (6).

The branch via dihydroxyacetonephosphate (6) is channelled back into D-glyceraldehyde-3-phosphate (5) in the fifth reaction by an isomerization. In the sixth reaction the combined D-glyceraldehyde- 3-phosphate from both routes is oxidized at the C1 to a carboxylic acid and then phosphorylated in the 1-position to yield 1,3-bisphospho-D-glycerate (7).

This phosphate group in the 1-position is transferred in the seventh reaction from the carboxyl group of (7) to ADP to give 3-phospho-D-glycerate (8).

The eighth reaction is an isomerization of 3-phospho-D-glycerate (8) to 2-phospho-D-glycerate (9).

The next metabolite phosphoenolpyruvate (10) is formed in a dehydration reaction from 2-phospho-D-glycerate in the ninth reaction.

The glycolysis pathway from D(+)-glucose (1) to two molecules of pyruvate (11) is concluded by the tenth reaction, which transfers a phosphate group from phosphoenolpyruvate (10) to ADP, thereby giving ATP and pyruvate (11).

Visit the Sigma Metabolomics Resource Center to view the Nicholson-IUBMB animation of glycolysis at http://www.sigma.com/metpath.

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