ATP as a Supply of Energy (Edexcel A (SNAB) A Level Biology)

• All organisms require a constant supply of energy to maintain their cells and stay alive
• This energy is required e.g.
  • For building new molecules from the products of digestion during anabolic reactions
  • To move substances across cell membranes in active transport or to move substances within cells
  • For muscle contraction 
  • In the conduction of nerve impulses
• In all known forms of life the molecule adenosine triphosphate, or ATP, is used to transfer and supply energy within cells
  • ATP is therefore known as the universal energy currency
  • ATP diffuses within cells to where it is needed

• ATP is a type of nucleic acid and is structurally very similar to the nucleotides that make up DNA and RNA
  • It is a phosphorylated nucleotide 
    • A nucleotide consists of a nitrogenous base, a sugar, and a single phosphate group
    • ATP contains three phosphate groups, hence triphosphate

ATP contains adenine, a ribose sugar, and three phosphates molecules. Removal of one phosphate creates ADP, and removal of two phosphates creates AMP.

• ATP is produced during respiration by the addition of inorganic phosphate (P_i), a type of phosphate group, to adenosine diphosphate, or ADP

ADP + P_i ATP 

• • ADP contains two phosphate groups, hence diphosphate
  • The breakdown of glucose in respiration releases the energy needed to phosphorylate ADP
• The hydrolysis, or breakdown, of ATP releases an inorganic phosphate as well as a small amount of energy which can be used by the cell

ATP  ADP + P_i 

• • The removal of a phosphate group is known as dephosphorylation
  • The hydrolysis of ATP is catalysed by the enzyme ATPase
• The ADP and inorganic phosphate produced by the hydrolysis of ATP can be recycled to make more ATP 

ADP + P_i ATP 

ATP is formed during respiration and can be hydrolysed to release energy for processes such as active transport, muscle contraction, and building new molecules (anabolic reactions). ATP can then be regenerated from ADP and phosphate.