• Without enzymes, metabolic reactions couldn't happen at the speed needed to sustain life
  • Reduce activation energy needed; without them reactions would have to happen at much higher temperatures
  • Induced fit hypothesis: the enzyme changes shape as the substrate molecule binds to the active site, and amino acids in the active site change to hold the substrate molecule in place
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Induced-fit hypothesis

  • Enzyme and substrate molecule collide; enzyme changes shape to make the active site fit around the molecule more closely
  • Oppositely charged groups on active site and substrate are close together, also holds substrate in place (enzyme-substrate complex)
  • As the enzyme changes shape, the substrate undergoes strain which destabilises it, making the reaction happen more easily
  • Products different shape from substrate, so no longer fit in active site; move away
  • Enzyme catalyses same reaction with a different substrate
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  • Molecules in a gas/liquid have natural kinetic energy; so constantly collide with each other
  • Temperature increases; kinetic energy increases. Molecules move faster and collide more often and with greater force
  • More collisions = more product = increased reaction rate
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Heat and denaturation

  • Applying heat makes molecules vibrate, putting strain on the bonds that hold the molecule together
  • In large molecules, vibration can break weaker bonds (H and ionic)
  • These bonds are the ones that hold the tertiary structure together, thus maintaining the shape of the active site
  • Increased heat = increased bond breakage
  • Structure loses the shape needed to keep the active site working
  • Thus, rate of reaction decreases
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pH effects

  • Measure of H+ concentration
  • H+ ions can interfere with H and ionic bonds of the tertiary structure of an enzyme; thus the concentration of H+ ions has a direct effect on how well the tertiary structure of an enzyme is held together
  • H+ ions attracted to negative groups on active site, thus alter charges around active site and change its shape
  • Optimum pH = tertiary structure shape that best accomodates substrate
  • Enzymes work in a considerably narrow pH range
  • Only denature when pH changes violently
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