12.1.1

Energy & ATP

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Hydrolysis of ATP

ATP is known as the "universal energy currency" of cells. Hydrolysis of ATP happens when a cell needs energy.

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ATP hydrolysis reaction

  • The equation for the hydrolysis of ATP is:
    • ATP + H2O → ADP + Pi (+ energy)
  • Hydrolysis of ATP to adenosine diphosphate (ADP) and an inorganic phosphate group (Pi) is catalysed by the enzyme ATP hydrolase.
    • This reaction uses a water molecule so is called a hydrolysis reaction.
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Energy release

  • Energy is released during the hydrolysis of ATP.
  • This energy is used to perform work inside the cell.
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Energy coupling

  • The hydrolysis of ATP can be coupled to other reactions within cells that need energy.
  • An example of energy coupling using ATP is the transmembrane sodium-potassium pump (Na+/K+ pump):
    • Energy is released from the hydrolysis of ATP.
    • Energy is needed to power the pump that drives Na+ out of the cell and K+ into the cell.
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Phosphorylation

  • The inorganic phosphate released in ATP hydrolysis can be used to phosphorylate other compounds.
  • This often makes the compounds more reactive.

Resynthesis of ATP

Like most chemical reactions, the hydrolysis of ATP to ADP is reversible.

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ATP resynthesis reaction

  • The equation for the resynthesis of ATP is:
    • ADP + Pi (+ energy) → ATP + H2O
  • ATP is resynthesised by the condensation of ADP and an inorganic phosphate.
  • This reaction is catalysed by the enzyme ATP synthase during photosynthesis or respiration.
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Formation of ATP requires energy

  • Cells rely on the regeneration of ATP just as people rely on the regeneration of spent money through some sort of income.
  • Since ATP hydrolysis releases energy, ATP regeneration must require an input of energy (just like earning money requires hard work!).

Jump to other topics

1Cell Structure

2Biological Molecules

3Enzymes

4Cell Membranes & Transport

5The Mitotic Cell Cycle

6Nucleic Acids & Protein Synthesis

7Transport in Plants

8Transport in Mammals

9Gas Exchange

10Infectious Diseases

11Immunity

12Energy & Respiration (A2 Only)

13Photosynthesis (A2 Only)

14Homeostasis (A2 Only)

15Control & Coordination (A2 Only)

16Inherited Change (A2 Only)

17Selection & Evolution (A2 Only)

18Classification & Conservation (A2 Only)

19Genetic Technology (A2 Only)

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