ATP

Universal Energy Currency

  • All biological Processes require energy. Energy comes in many forms - heat, light, energy in chemical bonds etc. Energy needs to be supplied to all processes that require it in the right quantity and form

Cells require energy for 3 main types of activity:

  • Synthesis - eg → protein synthesis

  • Transport - eg → pumping molecules or ions across cell membranes by active transport

  • Movement - eg → protein fibres in muscle cells that cause muscle contractions

Inside cells, molecules of ‘Adenosine Triphosphate’ (ATP) are able to supply this energy in a way to be used.

ATP used for energy transfer in all cells of all living things - Known as ‘universal energy Transfer’

Structure of ATP molecule

  • a nitrogenous base, a pentose sugar, 3 phosphate groups - ATP is a nucleotide

  • ATP base always = adenine, 3 Phosphate groups instead of one, sugar in ATP = ribose (same as RNA)

How ATP releases energy

  • Small amount of energy required to break a phosphate bond in ATP But overall reaction releases more energy than it costs.

  • As water is involved in removal of Phosphate group this is a ‘Hydrolysis reaction’ → ATP + H₂O → ADP + Pi + energy

ADP = adenosine Diphosphate Pi = inorganic phosphate

Condensation reaction would require energy to turn ADP into ATP - removing water and breaking bond with water and ATP

  • ATP - bad long term energy store due to instability of Phosphate bonds. Carbs and Fats = better solution

  • Energy released in the breakdown of Carbs and fats (in cellular respiration) is used to create ATP.

  • This occurs by reattaching Phosphate group to an ADP molecule - ‘Phosphorylation’. As water is removed in this process (because you’re replenishing the energy that was released when ATP + Water bonded) = Condensation reaction

  • Due to instability, high energy of ATP, cells do not store large amounts of it, However doesn’t matter as they keep plenty of ADP + Pi which are both low energy, stable. and therefore good because due to ‘Phosphorylation’, ADP + Pi can be converted back into ATP (condensation reaction) which is therefore used as immediate energy store.

Properties of ATP

  • Small - moves easily into / out of and within cells

  • Water soluble - energy requiring processes happen in aqueous environments

  • releases energy in small quantities - so energy isn’t wasted

  • Easily regenerated - easily recharged with energy

  • Contains Phosphate Bonds that release high enough energy when broken - useful for cellular reactions