Chapter 5. CATABOLISM AND CELLULAR BIOENERGETICS

Adenosine triphosphate (ATP) is an exclusive cellular energy currency. ATP provides energy to drive many processes in living cells, e.g., muscle contraction, nerve impulse propagation, transport of molecules, ion gradients, and chemical synthesis. ATP consists of adenine attached to a sugar (ribose), which in turn is attached to a triphosphate group (Fig. 5.1). ATP molecule contains 2 high-energy bonds between г and в, and б and в phosphate groups. These high-energy bonds store more energy than ordinary chemical bonds. During the hydrolyzis of г phosphate ~ 7.3 kcal/mol energy is released.

Fig. 5.1. Chemical structure of adenosine triphosphate (ATP)

The total quantity of ATP in the human body is about 0.2 moles, which is approximately 100 g and is enough to support cellular demand only for few seconds. Therefore, the cells need a constant ATP supply. In adult humans, approximately 100 to 150 moles (equivalent of 50 to 75 kg) of ATP are synthesized daily. ATP is synthesized mainly in oxidative metabolism and requires on average 27 moles of oxygen per day. A human will typically use up his or her body weight of ATP over the course of the day. In cellular energy metabolism, each ATP molecule is recycled (undergoes a process of hydrolyzis and synthesis) 500-750 times a day, which characterizes the intensity of ATP metabolism in the body.