The Importance Of ATP

Adenosine triophosphate (ATP) is an activated nucleotide found in all living cells that acts as an energy carrier. An ATP molecule is made up of three components: a ribose sugar molecule, a nitrogenous base (adenine) and three phosphates. At the centre of the molecule is the ribose sugar, which is then attached to adenine on one side and a chain of three phosphates on the other side. These phosphates are the key to the activity of ATP. It's role is to store and then release energy, when hydrolysed to form ADP (adenosine diphosphate) and an inorganic phosphate, which is then used for many metabolic processes. ATP is able to carry out its function of storing and releasing energy due to the bonds between the phosphate groups being unstable and therefore it has a low activation energy, meaning the bonds are easily broken and energy is released.

ATP is vital for many different processes in both animals and plants. An example is ATP's role in active transport. Active transport is the movement of substances from an area of low concentration to an area of high concentration - against the concentration gradient - with the use of energy. The energy required for active transport is provided by ATP and is used to change the shape of the protein carrier molecules so that molecules can be transported against a concentration gradient. One example of an active transport system is the sodium-potassium pump found in most animal cells. In this instance ATP is needed to bind to the protein pump, by being hydrolysed into ADP and a phosphate, to make it change shape so that both sodium and potassium ions can be moved. Active transport is also used in plants to move inorganic ions from the soil, which are low in concentration, into the root hair cells, where the concentration of ions is higher.

Another process that requires ATP is bioluminescence, which is the biochemical emission of light by living organisms, such as fireflies and deep-sea animals. Bioluminescence occurs through a chemical reaction that produces light energy within the organism. In order for bioluminescence to occur, an organism needs to possess special cells called photocytes which contain luciferin. Luciferin is the pigment that is oxidised when catalysed by the enzyme luciferase and this is the reaction that produces the light. This reaction however, also requires ATP in order to produce the light, as the enzyme reaction is coupled with the hydrolysis of ATP, where the majority of the energy released by ATP is transformed into light energy. In fireflies, the light produced is emitted from a special abdominal organ and is used by the organism to attract sexual mates or identify members of the same species. Unlike fireflies, deep-sea animals like the Hawaiian bobtail squid have taken in bacteria that are able to carry out bioluminescence into a special organ, in order to gain the ability to light up.

ATP is also the source of energy for muscle contraction, as ATP provides the energy needed for the filaments of the muscle to slide past one another to make the muscle fibre shorten. The main constituents of muscle fibres are the actin and myosin filaments, which are the filaments that slide over one another. This process requires calcium ions and ATP in order for the myosin filament to move the actin filament along. The calcium ions cause the binding sites on the actin filament to empty, so that the myosin can bind to the actin filament. Once attached, the myosin changes angle, which pulls the actin filament along, and then an ATP molecule binds to the myosin to detach it from the actin filament. After this, the calcium ions activate the enzyme ATPase, which hydrolyses the ATP to ADP, and the energy released causes the myosin to change back to its original angle. Therefore ATP is vital for muscle contraction to be a continuous process, as without it the myosin wouldn't be in the correct position to pull actin along.

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