ATP
By Jessica L. Schommer
The ATP molecule is a very important molecule in the biological world.
Organisms use ATP in biological oxidation reactions to produce energy to drive
thermodynamically unfavored processes such as protein synthesis or the break
down of sugars. The charge density on ATP is larger than its hydrolysis product,
ADP and theoretical studies show that ATP is more hydrated than ADP through the
semi-empirical heat of formation calculations. ATP is used to transfer the
terminal phosphate group to a substrate in a coupled ox/phos. reaction. It is
important to remember that ATP is stable in solution if an enzyme catalyst is
not present to drive hydrolysis, as can also be seen from the heat of formation
in solution for ATP.
A Spartan calculation showed the semi-empirical heat of formation for ATP to
be -1280.27 kcal/mol in a water solution.
ATP is 368.72 kcal/mol more stable in water than ADP!!
A map of the electrostatic potential helps to visualize why the ATP form is actually
more stable in water.