Hydrolysis of ATP
Do not refer to Pi as phosphorus or, even worse, as phosphorous
ATP can be broken down (hydrolysed) to give adenosine diphosphate (ADP) and an
inorganic phosphate group (Pi):
ATP hydrolase
ATP (+ H2O) → ADP + Pi
This conversion is catalysed by the enzyme
ATP hydrolase, sometimes called
ATPase.
Like other hydrolysis reactions, it involves water, but this is frequently ignored.
In fact water provides OH
- and H
+ and the covalently bonded phosphate is released as an inorganic ion HPO
42- + H
+.
Uses of ATP
The hydrolysis of ATP can be coupled to energy-requiring reactions within cells.
Examples:
Movement - muscular contraction involving actin and myosin requires energy from ATP, and so do other biological structures such as flagella.
Active transport - movement of any substance against a concentration gradient - requires the input of energy, and ATP powers the Na
+ /K
+ pump used in neurones, and also the uptake of nitrate ions by plant roots.
A number of
anabolic reactions such as synthesis of fats, polysaccharides, proteins and other categories of organic compounds require energy which is provided by ATP
Bioluminescence is another example of an energy-requiring process which is powered by ATP. This is very common in a variety of marine organisms and certain terrestrial arthropods.
In fact extracts from firefly tails containing
luciferin and luciferase may be used in laboratory for the assay of ATP.
What's made in the cell stays in the cell
In a multicellular organism, there are a number of organ systems providing raw materials for cells.
The digestive system breaks down a variety of food substances and deposits the soluble digestion products into the blood. Similarly, oxygen is taken into the lungs and absorbed into the bloodstream where it is carried by red blood cells using haemoglobin.
These substances are delivered by the circulatory system to all the cells of the body
collectively.
However once a cell has taken in what fuel and oxygen it needs, it uses it to produce ATP.
This ATP does not leave the cell.
Although cells work together with other cells in a tissue or organ to perform its function in a co-ordinated way, in energetic terms each cell acts
independently of other cells, each internally powering its own activity.