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Energy and ATP

Why do organisms need energy?

  • Metabolism- all reactions in the body
  • Movement- both within the organism and of the organism itself
  • Active transport- the movement of ions and molecules against the concentration gradient across a plasma membrane
  • Maintenance, repair and division
  • Production of substances- enzymes, hormones ect.
  • Maintenance of body temperature

The flow of energy

  • Light energy from sun ---> Chemical energy through photosynthesis ---> ATP through respiration ---> ATP used by cells

How ATP stores energy

  • The bonds between the three phosphate groups are unstable and can be broken easily, when they do a considerable amount of energy is released
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The synthesis and roles of ATP


  • The conversion of ATP to ADP + Pi is a reversible reaction, ATP ---> ADP + Pi =hydrolysis reaction, ADP + Pi ---> ATP =condensation reaction
  • Photophosphorylation- Takes place in chlorophyll containing plant cells during photosynthesis
  • Oxidative phosphorylation- Occurs in the mitochondria of plant and animal cells in the electron transport chain
  • Substrate-level phosphorylation- When phosphate groups are transferred from donor molecules to ADP to make ATP e.g. the formation of pyruvate in glycolysis

A good energy source because...

  • An immediate energy source
  • Releases less energy released than a glucose molecule- more manageble quantities
  • The hydrolysis of ATP to ADP is a single reaction
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Roles of ATP

  • Metabolic processes- ATP provides the energy to build up macromolecules from their basic units e.g. the synthesis of monosaccarides to polysaccarides
  • Movement- ATP provides the energy for the filaments of muscle to slide past eachother and therefore shorten the overall length of a muscle fibre
  • Active transport- Provides the energy to chage the shape of carrier proteins in plasma membranes,allowing ions/molecules to move against the concentration gradient
  • Secretion- ATP is needed to form the lysosomes necessary for the secretion of cell products
  • Activation of molecules- When a Pi is transferred from ATP to another molecule is make it more reactive and so lowers its activation energy. This allows enzymes-catalysed reactions to occur more readily e.g glycolysis
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