ABSTRACT
The molecules diffuse rapidly throughout the cell and thereby carry their bond energy from sites of energy generation to the sites where energy is used for biosynthesis and other cell activities. In the biosynthesis of macromolecules, this is accomplished by the transfer of phosphate groups to form reactive phosphorylated intermediates. Amino acids not used in biosynthesis can be oxidized to generate metabolic energy. Although cells contain a variety of small carbon-containing molecules, most of the carbon atoms in cells are incorporated into enormous polymeric moleculeschains of chemical subunits linked end-to-end. The making and breaking of covalent bonds are violent events, and in living cells they are carefully controlled by highly specific catalysts, called enzymes. One of the simplest kinds of chemical reaction, and one that has profound significance in cells, takes place when a molecule containing a highly polar covalent bond between a hydrogen and a second atom dissolves in water.
