ATP Flashcards
Why do cells require energy
-synthesis-for example of large molecules such as proteins
-transport-for example pumping molecules or ions across cell membranes by active transport.
-movement-for example protein fibres in muscle cells that cause muscle contraction.
What is adenosine triphosphate (ATP)
Inside cells, molecules of adenosine triphosphate (ATP) are able to supply this energy in such a way that it can be used.
An ATP molecule is composed of a nitrogenous base, a pentose sugar and three phosphate groups-it is a nucleotide. In ATP the base is always adenine and there are three phosphate groups instead of one. The sugar in ATP is ribose, as in RNA nucleotides.
ATP is used for energy transfer in all cells of living things. Hence it is known as the universal energy currency.
How ATP releases energy
Energy is needed to break bonds and is released when bonds are formed. A small amount of energy is needed to break the relatively weak bonds holding the last phosphate group in ATP. However, a large amount of energy is then released when the liberated phosphate undergoes other reactions involving bond formation. Overall a lot more energy is used.
Hydrolysis
As water is involved in the removal of the phosphate group this is another example of a hydrolysis reaction.
The hydrolysis of ATP doesn’t happen in isolation but in association with energy-requiring reactions. The reactions are said to be ‘coupled’ as they happen simultaneously.
ATP is hydrolysed into adenosine diphosphate (ADP) and a phosphate ion, releasing energy.
Hydrolysis ATP equation
Adenosine triphosphate+water-> adenosine diphosphate+inorganic phosphate+energy
Why is the instability of the phosphate bonds in ATP a problem
It is not a good long-term energy store. Fats and carbohydrates are much better for this. The energy released in the breakdown of these molecules (a process called cellular respiration) is used to create ATP. This occurs by reattaching a phosphate group to an ADP molecule. The process is called phosphorylation. As water is removed in this process, the reaction is another example of a condensation reaction.
Due to the instability of ATP, cells don’t store large amounts of it. However ATP is rapidly reformed by the phosphorylation of ADP. This interconversion of ATP and ADP is happening constantly in all living cells, meaning cells don’t need a large store of ATP. ATP is therefore a good immediate energy store.
Properties of ATP
The structure and properties of ATP mean that it is ideally suited to carry out its function in energy transfer. A summary of these properties is given below.
-Small-moves easily into, out of and within cells
-water soluble-energy-requiring processes happen in aqueous environments.
-contain bonds between phosphates with intermediate energy:large enough to be useful for cellular reactions but not so large that energy is wasted as heat.
-Releases energy in small quantities-quantities are suitable to most cellular needs, so that energy is not wasted as heat.
-Easily regenerated-can be recharged with energy.
