1.6.1

Structure of ATP

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Structure and Function of ATP

ATP is called a nucleotide derivative because it is a modified form of a nucleotide.

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Components of ATP

  • The components of ATP are:
    • Adenine - a nitrogenous base.
    • Ribose - a five-carbon sugar.
    • Three phosphate groups.
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Function of ATP

  • ATP is a small, relatively simple molecule.
  • This molecule can be thought of as the primary energy currency of cells.
    • ATP is the cell's equivalent of money, which people exchange for things they need.
  • ATP is used to power most energy-requiring cellular reactions.

Hydrolysis of ATP

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 as one of the phosphate bonds is broken.
  • 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

1Biological Molecules

2Cells

3Substance Exchange

4Genetic Information & Variation

5Energy Transfers (A2 only)

6Responding to Change (A2 only)

7Genetics & Ecosystems (A2 only)

8The Control of Gene Expression (A2 only)

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