Adenosine 5'-triphosphate

Adenosine 5'-triphosphate (ATP) is a complex organic chemical that provides energy to drive many processes in living cells, e.g., muscle contraction, nerve impulse propagation, and chemical synthesis. Found in all forms of life, ATP is often referred to as the "molecular unit of currency" of intracellular energy transfer. When consumed in metabolic processes, it converts either to adenosine diphosphate (ADP) or to adenosine monophosphate (AMP). Other processes regenerate ATP so that the human body recycles its own body weight equivalent in ATP each day. It is also a precursor to DNA and RNA, and is used as a coenzyme.

Structure

ATP consists of a nucleoside (adenosine) and three phosphate groups. The molecule is made up of a ribose sugar, with the adenine base attached to the first carbon atom and the chain of three phosphate groups bonded to the fifth carbon atom of the ribose. ATP is a highly charged molecule, with negative charges carried by its three phosphate groups.

Function

The primary role of ATP is to provide energy for various biological activities. Energy is released by hydrolysis of the terminal phosphate bond, which converts ATP to ADP and a free phosphate molecule, under the action of ATPase enzymes. This energy fuels many vital processes, including:

• Muscle contraction
• Nerve impulse propagation
• Chemical synthesis
• Active transport across cell membranes

ATP also plays a critical role in the synthesis of nucleic acids and is involved in cell signaling through its derivatives, such as cyclic AMP.

Biosynthesis

ATP is synthesized from ADP and phosphate through two main pathways: photophosphorylation in chloroplasts during photosynthesis and oxidative phosphorylation in mitochondria during cellular respiration. A smaller amount of ATP is produced by substrate-level phosphorylation during glycolysis and the citric acid cycle.

Regulation

The intracellular levels of ATP are regulated by a balance between ATP production and consumption. Cells maintain a high ratio of ATP to ADP to ensure a constant supply of energy. Various enzymes and cellular processes are sensitive to changes in this ratio, which serves as a signal for the metabolic state of the cell.

Clinical significance

ATP has been implicated in several diseases, including cancer, cardiovascular diseases, and mitochondrial diseases. It is also a target for some therapeutic interventions, such as in the treatment of myocardial infarction and certain types of pain management.

See also

• Adenosine
• Energy currency
• Metabolism
• Nucleotide