General Considerations

Abstract

Organisms require energy for the life processes such as growth and movement, and the energy is supplied in the most cases by adenosine 5′-triphosphate (ATP). When ATP is hydrolyzed by the catalysis of ATPase to adenosine 5′-diphosphate (ADP), energy of 7.3 kcal is released per mole (ca. 500 g). The organisms utilize this energy for their life processes. In general, a man with a body weight of 60 kg needs about 1800 kcal per day in normal life without carrying out hard work or extensive movement. If the total daily energy required by him is supplied only by the hydrolysis of ATP to ADP, he needs 124 kg ATP [1800÷7.3=247 (moles); 0.5 kg×247=124 kg]. It is impossible for him to hold a level of ATP of 124 kg in his body. The sum of the amounts of ATP and ADP present in one human body is only several tens of grams. Therefore, ADP formed by the hydrolysis of ATP has to be returned to ATP; ATP has to be used by a process of recycling. For this recycling, energy is necessary. To supply the energy, the human being needs to consume food, and bacteria also require nourishment. Furthermore, in the case of the photosynthetic organisms, light is required. However, in this book the photosynthetic organisms are not included except for a brief explanation. The food for bacteria varies according to the organism (Fig. 1.1).