ATP—the Universal Energy Currency - Calango Free Online Courses
Welcome to ATP—the Universal Energy Currency lesson on Introduction to Chemistry: General, Organic, and Biological course, we are delighted to have you here.
Describe the importance of ATP as a source of energy in living organisms.
The pyrophosphate bond, symbolized by a squiggle (~), is hydrolyzed when ATP is converted to adenosine diphosphate (ADP). In this hydrolysis reaction, the products contain less energy than the reactants; there is a release of energy (> 7 kcal/mol). One reason for the amount of energy released is that hydrolysis relieves the electron-electron repulsions experienced by the negatively charged phosphate groups when they are bonded to each other (Figure 20.3 "Hydrolysis of ATP to Form ADP").
Figure 20.3 Hydrolysis of ATP to Form ADP
ATP + H2O → ADP + Pi + 7.4 kcal/mol
Pi is the symbol for the inorganic phosphate anions H2PO4− and HPO42−.
ATP is not the only high-energy compound needed for metabolism. Several others are listed in Table 20.1 "Energy Released by Hydrolysis of Some Phosphate Compounds". Notice, however, that the energy released when ATP is hydrolyzed is approximately midway between those of the high-energy and the low-energy phosphate compounds. This means that the hydrolysis of ATP can provide energy for the phosphorylation of the compounds below it in the table. For example, the hydrolysis of ATP provides sufficient energy for the phosphorylation of glucose to form glucose 1-phosphate. By the same token, the hydrolysis of compounds, such as creatine phosphate, that appear above ATP in the table can provide the energy needed to resynthesize ATP from ADP.
Table 20.1 Energy Released by Hydrolysis of Some Phosphate Compounds