Uses of ATP for Cellular Function. Energy from ATP is used to promote three major
categories of cellular functions:(1) transport of substances through multiple membranes in the cell, (2)
synthesis of chemical compounds throughout the cell, and (3) mechanical work. These uses of ATP are
illustrated by examples in Figure 2-15: (1) to supply energy for the transport of sodium through the
cell membrane, (2) to promote protein synthesis by the ribosomes, and (3) to supply the energy needed
during muscle contraction. In addition to membrane transport of sodium, energy from ATP is required
for membrane transport of potassium ions, calcium ions, magnesium ions, phosphate ions, chloride
ions, urate ions, hydrogen ions, and many other ions and various organic substances. Membrane
transport is so important to cell function that some cells—the renal tubular cells, for instance—use as
much as 80 percent of the ATP that they form for this purpose alone. In addition to synthesizing
proteins, cells make phospholipids, cholesterol, purines, pyrimidines, and a host of other substances.
Synthesis of al most any chemical compound requires energy.
