ATP drives cellular work.
<P>
   Phosphate group transfer provides energy for most cellular work.
<P>
<lI> ATP drives active transport by phosphorylating membrane proteins.
<lI> ATP drives mechanical work by phosphorylating motor proteins, such
as those that move vesicles along cytoskeleton "tracks".
<P>
   After  work  is done, the phosphate is released as inorganic phosphate
   (Pi).