In oxidation there is the loss of an electron and in reduction, the gain of an electron. As in spontaneous oxidation-reduction reactions, electrons move from a higher energy level to a lower one, the molecule releases energy when it oxidizes. When glucose is oxidized, the CC, CH, and OO bonds are exchanged for CO and HO bonds, since oxygen accepts electrons.
The equation can be summarized like this:
Glucose + oxygen → carbon dioxide + water + energy
C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O ΔG = -686 kcal / mol
Glucosa + oxígeno → dióxido de carbono + agua + energía
C6H12O6 + 6O2 → 6CO2 + 6H2O ΔG = -686 kcal/mol
In living beings, 40% of the energy produced by the oxidation of glucose is stored in the bonds that lead to transform ADP into ATP.
The breakdown of glucose takes place in two stages:
- Glycolysis: takes place in the cytoplasm of the cell. The glucose molecule (six carbons) is divided into two pyruvic acid molecules (composed of three carbons). Electrons are not accepted by oxygen, but by NAD+. The free energy change represents a relatively small proportion of the total energy of the glucose molecule.
- Respiration: takes place in the mitochondria. Electrons and protons are accepted by oxygen, obtaining great energy efficiency. Breathing consists of two stages: