Glucose is an important fuel for most organisms, and glycolysis is the main pathway that enables it to be used. The word glycolysis simply means the breakdown of glucose. It is an ancient pathway that can function without oxygen and indeed is thought to have evolved before there was much oxygen in the atmosphere. The pathway is present in almost all cells and takes place in the cytosol. It is shown in Figure 13.3.
1. Free glucose is phosphorylated on carbon 6 to produce glucose-6-phosphate. As we discussed earlier (page 258), this reaction, catalyzed by hexokinase, is driven by the free energy available from ATP.
2. Glucose-6-phosphate is isomerized to fructose 6-phosphate.
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