Enzymes

Enzymes

1. Enzymes speed up chemical reactions by acting as biological catlysts

2. They catalyse metabolic reactions in the body, digestion, respiration

3. Enzyme action can be intracellular or extracellular

4. Enzymes are globular proteins

5. Activation energy

   • The amount of energy needed to start a chemical reaction
     • Often provided as heat
   • Enzymes lower the activation energy needed, often making the reaction happen at a lower teperature than they could without an enzyme
     • This speeds up the rate of reaction

6. Enzyme substrate complex

   • When a substrate fits into the enzymes active site it forms an enzyme substrate complex
   • This lowers the activation energy
   • If two substrate molecules need to be joined, being attached to the enzyme holds them close together
     • This reduces any repulsion between the molecules so they can bond more easily
   • If the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on the bonds in the substrate
     • So the substrate molecule breaks up more easily

7. Lock and key model

   • Enzymes only work with substrates that fit their active site

8. Induced fit model

   • The substrate doesn't only have to be the right shape to fit the active site
   • The substrate has to make the active site change shape in the right way aswell

9. 3D structure

   • Enzymes are very specific and usually only catalyse one reaction
     • This is because only one substrate will fit into the active site
   • The active site's shape is determined by the 3D structure
     • Which is determined by the enzyme's primary structure
   • If the 3D structure of a protein is altered in any way, the shape of the active site will change

10. Concentration

    • The more enzyme molecules there are, the more likely a substrate molecule will collide with one and form an enzyme substrate complex
    • Increasing the concentration of the enzyme increases the rate of reaction
    • If the amount of substrate is limited, even if more enzyme is added there will be no reaction, adding more enzyme has no further effect