The Structure & Nature of ATP

ATP is a nucleotide which means it is composed partly of one of the same molecules found in a strand of DNA (adenine = one of the 4 DNA bases). It even has a ribose molecule. See diagram 1 below.

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However in the case of ATP, it is described as a phosphorylated nucleotide because it has three phosphate groups attached. Note that it does not have 3 phosphates attached! The proper description is phosphate groups.

Phosphate is: - an atom of phosphorous plus 4 oxygen atoms.

Phosphate PO₄ ^3-

Phosphate has 3 extra electrons (3^-)

ATP contains much energy but that energy needs to be released. All that ATP needs is the presence of water and it becomes hydrolysed.

At first the end phosphate group is hydrolysed and as it breaks from the main molecule, free energy is released in the order of 30.6kJ. A second phosphate group is hydrolysed and the same energy yield is made.

• Hydrolysis of ATP yields 30.6kJ free energy = ATP > ADP
• Hydrolysis of ADP yields 30.6kJ free energy = ADP > AMP

After this, the final phosphate group yields less energy.

Generally only ATP > ADP occurs

• A phosphate group is freed by hydrolysis. It is almost immediately re-attached to an ADP molecule by rephosphorylation.

This occurs through respiratory activity [oxidative phosphorylation] or even another respiratory compound.

• Oxidative phosphorylation = ADP > ATP. This is the electron transport chain (ETC).