⚡️ATP ⚡️

• Cells require energy for three main types of activity:

  • synthesis e.g. of large molecules such as proteins
  • transport e.g. pumping molecules or ions across cell membranes by active transport
  • movement e.g. protein fibres in muscle cells that cause muscle contraction
  • Inside cells, molecules of adenosine triphosphate (ATP) supply this energy
• ATP is similar in structure to a nucleotide, its composed of a nitrogenous base (always adenine), a pentose sugar (ribose), and three phosphate groups
• How ATP releases energy:

  ATP + water -> ADP (adenosine diphosphate) + inorganic phosphate (Pi) + energy

  ATP is hydrolysed into ADP and a phosphate ion, releasing energy

  The phosphate group that is released from the ATP is the last one
• The hydrolysis of ATP does not happen in isolation but in association with energy-requiring reactions

  The reactions are said to be 'coupled' as they happen simultaneously.
• A small amount of energy is needed to break the relatively weak bond holding the last phosphate group in ATP
• The instability of the phosphate bonds in ATP means its not a good long-term energy store

  Fats and carbohydrates are much better.

  The energy released in the breakdown of fats and carbs (i.e. cellular respiration) is used to create ATP
• ATP is produced by the addition of a phosphate group to an ADPm molecule by a condensation reaction.

  This is called phosphorylation
• The instability of ATP means large amounts of it are not stored but it is rapidly reformed by the phosphorylation of ADP.

  This interconversion of ATP and ADP happens constantly in all living cells so a large store of ATP is not needed
• ATP is a good immediate energy store
• The properties of ATP are:

  • it's small- it moves easily into, out of, and within cells
  • it's water soluble- energy-requiring processes happen in aqueous environments
  • it contains bonds between phosphates with intermediate energy that is large enough to be useful for cellular reactions but not so large that energy is wasted as heat
  • it's easily regenerated