ATP (Adenosine triphosphate)

• It is the major energy currency of the cell, providing the energy for most of the energy-consuming activities of the cell.
• It is one of the monomers used in the synthesis of RNA and, after conversion to deoxyATP (dATP), DNA.
• it regulates many biochemical pathways

Energy

When the third phosphate group of ATP is removed by hydrolysis, a substantial amount of free energy is released. The exact amount depends on the conditions, but we shall use a value of 7.3 kcal per mole.

ADP is adenosine diphosphate. P_i is inorganic phosphate [structure]

For this reason, this bond is known as a "high-energy" bond and is depicted in the figure by a wavy red line. (The bond between the first and second phosphates is also "high-energy".) (But please note that the term is not being used in the same sense as the term "bond energy". In fact, these bonds are actually weak bonds with low bond energies.)

Synthesis of ATP

• ADP + P_i -> ATP + H₂O
• requires energy: 7.3 kcal/mole
• occurs in the cytosol by glycolysis
• occurs in mitochondria by cellular respiration
• occurs in chloroplasts by photosynthesis

Consumption of ATP

Most anabolic reactions in the cell are powered by ATP. Examples:

assembly of amino acids into proteins

assembly of nucleotides into DNA and RNA

synthesis of polysaccharides

synthesis of fats

active transport of molecules and ions

nerve impulses

maintenance of cell volume by osmosis

muscle contraction