AQA A Level Biology

Revision Notes

1.6.2 Hydrolysis & Synthesis of ATP

Hydrolysis of ATP

  • Energy released during the reactions of respiration is transferred to the molecule adenosine triphosphate (ATP)
  • ATP is a small and soluble molecule that provides a short-term store of chemical energy that cells can use to do work
  • It is vital in linking energy-requiring and energy-yielding reactions
  • ATP is described as a universal energy currency
    • Universal: It is used in all organisms
    • Currency: Like money, it can be used for different purposes (reactions) and is reused countless times
  • The use of ATP as an ‘energy-currency’ is beneficial for many reasons:
    • The hydrolysis of ATP can be carried out quickly and easily wherever energy is required within the cell by the action of just one enzyme, ATPase
    • A useful (not too small, not too large) quantity of energy is released from the hydrolysis of one ATP molecule – this is beneficial as it reduces waste but also gives the cell control over what processes occur
    • ATP is relatively stable at cellular pH levels

Hydrolysis of ATP

  • Hydrolysis of ATP to adenosine diphosphate (ADP) and an inorganic phosphate group (Pi) is catalysed by the enzyme ATP hydrolase sometimes called ‘ATPase’
  • The hydrolysis of ATP can be coupled to energy-requiring reactions within cells such as:
    • The active transport of ions up a concentration gradient
    • Enzyme controlled reactions that require energy
    • Muscle contraction and muscle fibre movement
  • As ADP forms free energy is released that can be used for processes within a cell eg. DNA synthesis
    • Removal of one phosphate group from ATP releases 30.8 kJ mol -1 of energy, forming ADP
    • Removal of a second phosphate group from ADP also releases 30.8 kJ mol-1 of energy, forming AMP
    • Removal of the third and final phosphate group from AMP releases 14.2 kJ mol-1 of energy, forming adenosine
  • The inorganic phosphate released during the hydrolysis of ATP can be used to phosphorylate other compounds, often making them more reactive

Features of ATP Table

Features of ATP table, downloadable AS & A Level Biology revision notes

Exam Tip

Be careful not to use the terms energy and ATP interchangeably. Energy is the capacity or power to do work. ATP is a molecule which stores (chemical potential) energy and carries it to places in the cell that need energy to do work. “Energy” cannot be produced or destroyed whereas an ATP molecule can be – therefore in biology reactions that require energy ‘use ATP’ or ‘require the hydrolysis of ATP’ and reactions that synthesise ATP do not ‘produce energy’.

ATP Synthesis

  • On average humans use more than 50 kg of ATP in a day but only have a maximum of ~ 200g of ATP in their body at any given time
  • Organisms cannot build up large stores of ATP and it rarely passes through the cell surface membrane
  • This means the cells must make ATP as and when they need it
  • ATP is formed when ADP is combined with an inorganic phosphate (Pi) group by the enzyme ATP synthase
    • This is an energy-requiring reaction
    • Water is released as a waste product (therefore ATP synthesis is a condensation reaction)

Types of ATP synthesis

  • ATP is made during the reactions of respiration and photosynthesis
    • All of an animal’s ATP comes from respiration
  • ATP can be made in two different ways:
    • Substrate-linked phosphorylation (occurs in the glycolysis stage of respiration)
    • Chemiosmosis (occurs in the electron transport chain stage of respiration)

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