1.8 Factors Effecting Enzyme Action

1.8 Factors Effecting Enzyme Action

1. Temperature

   • A higher temperature means the substrate and enzyme molecules have more kinetic energy and move around more
     • More collisions
       • MORE ENZYME-SUBSTRATE COMPLEXES FORMED
         • The way this speeds up the reaction, is because the enzyme and substrate molecules come together to produce MORE enzyme-substrate complexes in a given time. 
         • Faster Rate of Reaction
   • There is an optimum temperature
     • Any temperature higher than the enzymes optimum will have enough energy to break the bonds that hold the enzyme in shape
       • So therefore past the optimum, the enzyme becomes DENATURED
         • It is no longer functional

2. pH

   • All enzymes have a maximum pH value
     • They also have a minimum
   • The pH of a solution is also a measure of its hydrogen ion concentration
   • Above and below the optimum (maximum) pH, the H+ ions and OH- Ions ound in acids and alkali's can mess up the ionic and hydrogen bonds holding the enzymes tertiary structure in place
     • So on either side of the optimum, the enzyme can be DENATURED!
   • A change in pH alters the charges on the amino acids that make up the active site of the enzyme.
     • As a result, the substrate can no longer attach to active site = NO ENZYME-SUBSTRATE COMPLEXES FORMED
       • The phrase "ENZYME-SUBSTRATE COMPLEXES" is in capitals because in your exam, that phrase, is key. In most enzyme questions there will be one mark just for that small phrase - easy marks!

3. Enzyme Concentration

   • Once an active site of an enzyme has acted on its substrate, it is free to repeat the procedure on another substrate molecule
   • More enzyme molecules in a solution
     • more likely substrate is to collide with one and form an ENZYME-SUBSTRATE COMPLEX
       • therefore: Increasing the concentration of enzyme increases the rate of reaction
   • However, if the amount of substrate is limited
     • Increase in enzyme concentrate eventually has no further effect

4. Substrate Concentration

   • Higher the substrate concentration, the faster the reaction
     • this is because collisions become more likely and more active sites will be used
       • More ENZYME-SUBSTRATE COMPLEXES
   • Saturation Point
     • All active sites are full/in use
       • Substrate concentration makes no difference
   • Substrate conc. decreases with time during a reaction (unless more is added to reaction mixture)
     • If no other variables changed, rate of reaction will decrease over time too
       • This means initial rate of reaction = highest rate of reaction

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