ATP, shorthand for adenosine triphosphate, is the standard molecule for cellular enger in the human body. All motion and metabolic processes within the body begins with energy that is released from ATP, as its phosphate bonds are broken in cells through a process called hydrolysis. Once ATP is used, it is recycled through cellular respiration where it gains the needed phosphate ions to store energy again.
ATP macromolecules are referred to as the main "energy currency of the cell" and transfers potential energy on the cellular level through chemical bonds. All metabolic processes that occur on the cellular level are powered by ATP. When ATP releases one or two phosphate ions, energy is released as the chemical bonds between the phosphate ions are broken. According to TrueOrigin, nearly 400 pounds of ATP are used daily by the ordinary human with a 2,500 calorie diet. As an energy source, ATP is responsible for transporting substances across cell membranes and performs mechanical work of muscles contracting and expanding, including the heart muscle.
One of the many uses of ATP is the physical movement of muscles. During musclular contraction, myosin heads attach to bonding sites on the actin myofiliaments through the use of an ADP (adenosine diphosphate) cross-bridge, where the extra phosphate ion from ATP is released. ADP differs from ATP in that it lacks the third phosphate ion that gives ATP its energy-releasing capabilities. Energy stored from the releasing of the phosphate allows the myosin to move its head, which is currently bonded to, and thus moves with the actin. ATP bonds with the myosin head after muscle contraction is complete and is converted to ADP (adenosine diphosphate) with an extra phosphate ion.
DNA and RNA Synthesis
When cells divide and undergo the process of cytokinesis, ATP is used to grow the size and energy content of the new daughter cell. The ATP is used to trigger DNA synthesis, where the daughter cell receives a complete copy of the DNA from the parent cell. ATP is a key component in the DNA and RNA synthesis process as one of the key building blocks used by RNA polymerase to form the RNA molecules. A different form of ATP is converted to a deoxyribonucleotide, known as dATP, so that it can be incorporated into DNA molecules for DNA synthesis.
By bonding with certain parts of protein molecules, ATP can act as an On-Off switch for other intracellular chemical reactions and can control messages that are sent between different macromolecules within the cell. Through the bonding process, ATP causes another part of the protein molecule to change its arrangement, thus making the molecule inactive. When ATP releases its bond from the molecule, it reactivates the protein molecule. This process of adding or removing a phosphorus from a protein molecule is referred to phosphorylation. One example of ATP being used in intracellular signaling is the release of calcium for cellular processes in the brain.