ATP: The Energy Currency

ATP, or adenosine triphosphate, is a nucleotide made of adenosine coupled to three phosphate molecules. Adenosine is made up of adenine and ribose. When the body's cells need energy, the phosphate groups are broken off the ATP molecule, first making adenosine diphosphate (ADP), then adenosine monophosphate (AMP), and finally simply adenosine. Adenosine is then further broken down by the cell to its metabolic products adenine, hypoxanthine, and inosine which ultimately wash out of the cell (metabolically, ribose changes when the molecule is made and is thus not part of the breakdown). The conversion of ATP to ADP produces the most energy; ADP to AMP produces some energy; AMP to adenosine produces very little energy.

In normal body conditions, ATP is converted to ADP, which is quickly reconverted back to ATP when oxygen is present through the metabolism of glucose. However, when insufficient oxygen exists to metabolize glucose properly (as in anaerobic work), ATP cannot be regenerated. In this case, ATP may be broken all the way down to adenosine. When this happens, the molecules required to rebuild ATP may be lost from the cell and must be replaced. If they are not replaced quickly, the cell will not have sufficient energy to perform normal cellular functions. The heart may not beat properly and other muscles may not relax and contract normally.

ATP provides virtually all the energy needed by the body and is the only source of energy for the cell. The energy released from the breakdown of the ATP molecule is used to power all bodily functions, which is why ATP is considered the "energy currency" of the cell. Proper ATP levels must be maintained for normal cellular function. If ATP degenerates past the point of renewal, the energy needed by the cells is lost. Ribose, as a precursor to adenosine, can help reverse this condition.

—E.B.