Chemical energy in cells

All food contains chemicals. These chemicals are the source of energy. The energy can be released in several ways. The chemical bonds in ATP (adenosine triphosphate) are termed ‘high-energy’ bonds and the processes of oxidation and reduction are involved in making and breaking these.
Oxidation is a process of electron loss or the uptake of oxygen or removal of hydrogen from a molecule. Reduction is the opposite of all these. Whenever something is oxidized then the substance that does the oxidizing is itself reduced (for details of these concepts see Chapter 10). An example of this process are two
materials present in cells, lactic acid and pyruvic acid. They undergo an interchange of oxidation and reduction (Figure 4.10). Some of the energy released in this, and many other, oxidation reactions of the body converts low-free energy ADP in the presence of a little more phosphate into high-free energy ATP. This contains highenergy phosphate bonds. The energy stored in the ATP can be transferred to other molecules when required in anabolic processes.


The efficient inter-conversion of molecules in the cells to give out, and take in, energy occurs in the presence of other ‘carrier’ chemicals. These are a basic set of reactions that keep us supplied with energy. These reactions occur smoothly and efficiently within the cell but are difficult to do in a ‘test tube’ reaction in the laboratory. This shows how well designed the cell processes really are. The wider, more elaborate cycle of events and chemical reactions is called the Krebs cycle.