A level Biology notes – ATP

What is ATP:

  • Currency of energy in cells
  • Used as the energy source to carry out processes
  • A molecule which transfers immediate energy for biology processes


The synthesis of ATP, its role and properties

Biological processes that ATP provides energy for:

  • Activation of molecules
  • Metabolism
  • Movement within an organism (circulation of blood) and movement of organism
  • Active transport
  • Secretion
  • Maintenance of body temperature
  • Maintenance, repair and division of cells and organelles
  • Production of substances used in organisms


How ATP stores energy

ATP has 3 phosphate groups and the bonds between these groups are unstable and so have low activation energy. This means that they are easily broken. Energy is stored in these chemical bonds when the phosphate is released and the bonds are broken in hydrolysis, energy is released.


Synthesis of ATP

Conversion of ATP and ADP is when energy is used to add an inorganic phosphate to ADP to re-form ATP.

  • ATP is converted to ADP by hydrolysis using the enzyme, ATPase. Energy is released for us by cells.
  • ADP and Pi (inorganic phosphate) convert to ATP during condensation using the enzyme, ATP synthase. Energy is supplied from respiration

The phosphate is added in 3 ways (phorylation):

Photophorylation (from light) – occurs in chlorophyll-containing plant cells during photosynthesis

Oxidative phosphorylation (from respiration) – occurs in the mitochondria during electron transport

Substrate-level phosphorylation – occurs in cells when phosphate groups are transferred from donor molecules to ADP to make ATP

A metabolic process is a series of reactions occurring in a specific sequence. ATP provides energy needed to build up macromolecules from their basic units.

ATP is an immediate energy source because the phosphate bonds are unstable so the hydrolysis of ATP to ADP is a single reaction that releases energy directly to where its needed.


Advantages of using ATP rather than glucose as a source of energy:

  • ATP is released in smaller and more manageable quantities
  • Hydrolysis of ATP to ADP is a single reaction whereas glucose is a serious of reactions
  • ATP is easily broken down, its soluble so it’s easily transported, it can’t pass out the cells

ATP can’t be stored because it is unstable so it hydrolyses easily and is soluble.


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