1.7 Enzyme Action

Biological Catalysts
Enzymes lower the activation energy of metabolic reactions
1. Reactions can take place at lower temperatures
  1. E.g/ 37 degrees - Body temperature
  2. Faster Rate of Reaction
2. Substrate fits into enzymes active site = ENZYME-SUBSTRATE COMPLEX formed
  1. 1) If two substrate molecules need to be joined, being attached to enzyme holds them close together, reducing repulsion so they can bond more easily
  2. 2) If the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate so the substrate molecules breaks up more easily
The Lock and Key model
1. Each enzyme has a specifically shaped active site, where only one shape of substrate fits perfectly, like a key in a lock.
The Induced Fit Model
1. Substrate doesn't perfectly fit active site
  1. Substrate makes the active site change shape so the substrate can interact with the enzyme
    1. Enzyme can 'mould' itself around the substrate which is why it is very SPECIFIC
      1. When enzyme fits around substrate, strain is put on the substrate and a paticular bond or bonds in the substrate and lowers the activation energy needed to break the bond
Enzyme Properties relate to their Tertiary Structure
1. Enzymes are very specific as they only catalyse one reaction. E.g/ Sucrase only breaks down sucrose
2. This is because its the tertiary structure (which is determined by the primary structure) that determines the shape of the active site!
3. Different Enzyme = Different tertiary structure = Different active site shape
4. If tertiary structure changed in any way, shape of active site will also change
  1. Substrate won't fit into changed active site
    1. No ENZYME-SUBSTRATE COMPLEXES
      1. Reaction will not be catalysed
  2. Temperature
  3. pH

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1.7 Enzyme Action

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