Is ATP free energy?

A free energy system consists of the flow of ATP molecules through the cell body. When ATP molecules reach their resting form, they are converted by adenosine triphosphate (ATPase) to adenosine, an energy source which requires energy to maintain. The following steps will show that ATP free energy remains unchanged with time in the cell

1. The rate of accumulation of ATP free energy decreases (doubles).

2. The rate of depletion of ATP free energy increases (doubles).

The following table shows the equilibrium reaction potentials of a wide range of free energy systems. There are the adenosine, glycogen, glucose and fatty acids (or ketones) free energy systems that are used to generate energy (in the amount needed to sustain life)


Energy Source

Rate of


(ATP vs. ATP)

(%/min or % for glucose/fat) Free Energy Total



(wet or dry) A. Adenosine ATP

free energy

molecule % ATP

free energy

molecule % ATP

free energy

molecule % Glycerol 100 % 17 % 15 % 2.5

1 Carbohydrate 50 % 20 % 17.5 2.5

1 Alcohol 15 % 17.5 2.5

1 Lipids 9 % 14.5 15 20


(In this table glucose is called the free energy supply while glycogen is also a system of energy synthesis. Glycogen does not require anything from the environment to be made and used (as is ATP) so therefore it does not affect the breakdown of carbohydrates. The rate of glycerol and fatty acid metabolism is very similar to the rate of starch synthesis (the glyco-pathway). The rates of glycerol and fatty acid metabolism are the same for all energy systems. The only difference between sugar and starch is that sugar will generate an increase in glucose free energy (see the glyco-pathway and the rate of starch production), whereas starch will generate an increase in the free energy generated as a by-product.

2. Since ATP is used to create new energy in all of the energy systems, the free energy and total free energy need never be the same. Even a small increase in energy availability can produce a large change in the amount of ATP and the

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