When we burn wood, we release the chemical energy stored in wood. This energy is given off in the form of light and heat. Carbon dioxide and water are the products of this reaction.

All cells need energy in chemical form. They get this energy by breaking down nutrient compounds, such as glucose. The breakdown of glucose occurs through several metabolic pathways, beginning with glycolysis.

Glycolysis is a series of ten reactions in which one glucose molecule is broken down into two pyruvate molecules. This anaerobic process is the most universal of all the metabolic pathways, occurring essentially the same way in all organisms, both aerobic and anaerobic, which suggests that it was the first metabolic pathway to evolve.

In most cells, glucose is metabolized aerobically—in the presence of free oxygen. It’s completely oxidized to carbon dioxide and water, releasing the maximum amount of energy. In some cancers, there isn’t enough oxygen available to completely oxidize glucose, so the cancer cells get most of their energy through glycolysis.

Glycolysis takes place in the cytoplasm. The purpose of glycolysis is to generate ATP, the cell’s energy currency. As glucose is oxidized, NAD is reduced. Some of the energy released by glycolysis is stored in the reduced form of NAD, NADH.

The flow of metabolites through metabolic pathways may be increased or decreased depending on the needs of the organism. This can be accomplished by regulating the activity of one or more enzymes in the pathway. Enzymes regulated by the presence of activators and inhibitors catalyze three of the ten reactions of glycolysis- reactions 1, 3, and 10.

The first regulated reaction of glycolysis is catalyzed by the enzyme hexokinase. If this reaction is blocked in a cell, all of glycolysis is blocked, and the cell will die. Cancer researchers are trying to find a way to turn hexokinase off to kill cancer cells.

In this activity, we’ll start with an overview of glycolysis and its ten reactions. Next, we’ll see what happens to pyruvate and NADH under aerobic and anaerobic conditions. Finally, we’ll look at how the regulation of glycolysis illustrates the general principles that apply to the regulation of all biochemical pathways.

Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education