1.7 Enzyme Action

1.7 Enzyme Action

1. Biological Catalysts

2. Enzymes lower the activation energy of metabolic reactions

   • Reactions can take place at lower temperatures
     • E.g/ 37 degrees - Body temperature
     • Faster Rate of Reaction
   • Substrate fits into enzymes active site = ENZYME-SUBSTRATE COMPLEX formed
     • 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) 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

3. The Lock and Key model

   • Each enzyme has a specifically shaped active site, where only one shape of substrate fits perfectly, like a key in a lock.

4. The Induced Fit Model

   • Substrate doesn't perfectly fit active site
     • Substrate makes the active site change shape so the substrate can interact with the enzyme
       • Enzyme can 'mould' itself around the substrate which is why it is very SPECIFIC
         • 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

5. Enzyme Properties relate to their Tertiary Structure

   • Enzymes are very specific as they only catalyse one reaction. E.g/ Sucrase only breaks down sucrose
   • This is because its the tertiary structure (which is determined by the primary structure) that determines the shape of the active site!
   • Different Enzyme = Different tertiary structure = Different active site shape
   • If tertiary structure changed in any way, shape of active site will also change
     • Substrate won't fit into changed active site
       • No ENZYME-SUBSTRATE COMPLEXES
         • Reaction will not be catalysed
     • Temperature
     • pH

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