An exemplary biology essay
ATP (adenosine triphosphate) is vital to living organisms. It acts as a short-term store of energy in a cell, carrying it from where it is synthesised (e.g. the mitochondria) to where it is needed for biological processes. It is well suited to this job for the following reasons: it is small and soluble (and so can be easily transported around a cell); it is easily broken down to release energy; it can transfer energy to other molecules; and it cannot leave the cell. All of these facts mean that ATP is always available to the cell as an immediate source of energy.
ATP consists of adenine, ribose (adenosine) and a chain of three phosphates. The phosphates are joined to the adenosine molecule by phosphate bonds. It is the terminal phosphate bond that is involved in the short-term storage and easy release of energy. This bond is unstable, and so easily broken, giving adenosine diphosphate (ADP) and an inorganic phosphate (Pi). Hydrolysis of this bond releases the chemical energy stored by ATP so that it can be used by the cell. The products of this hydrolysis can be used to create another molecule of ATP.
ATP has several advantages over the other sources of energy in a cell, such as starch and glucose, for several reasons. It is necessary for a cell’s main source of energy to diffuse across the cell easily and quickly, and being far smaller than both glucose and starch, and soluble (unlike starch) ATP is far more suited to this job. The simple, single reaction that is required to release energy from ATP is much quicker than the series of reactions that would be required to break down either starch or glucose, and releases far less energy. This means that the exact amount of energy that is required can be released as soon as it is needed.
As mentioned above, a molecule of ATP can be synthesised from a molecule of ADP and an inorganic phosphate, in a process called phosphorylation. The most