Factors Affecting Enzyme Activity

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  • increasing the temperature of a reaction environment increases the kinetic energy of the particles, this means they move faster and so there are more frequent successful collisions between substrate and enzyme --> an increase in the rate of reaction 
  • Temperature coeffecient- Q10' --> for an enzyme controlled reaction, it measures how much the rate of reaction increases with a 10°C temperature increase (usually doubles)


  • With higher temperatures, bonds holding the protein together vibrate, they're strained and break. This changes the precise tertiary structure
  • The active site has changed shape- no longer complementary to the substrate so the enzyme can no longer function as a catalyst 

Optimum Temperature:

  • the temperature at which the enzyme has the highest rate of reactivity
  • when denatured above the optimum temperature, decrease in rate is rapid 
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Temperature Graph


  • 1 --> rate increases as the temperature increases because the particles have more kinetic energy. This means there is an increased chance of successful collisions between enzyme and substrate so there is an increased no. of enzyme-substrate complexes 
  • 2 --> the optimum temperature, highest rate of reaction
  • 3 --> bonds within the tertiary structure of the enzyme denature at temperatures above the optimum, This means the active site is no longer complementary to the substrate 
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  • Hydrogen bonds and ionic bonds between amino acid R groups hold proteins in their precise shapes
  • pH refers to a change in hydrogen concentration. More H+ present in a low pH (acid).  Less H+ present in high pH (alkali)
  • The active site is only in the right shape at certain H+ concentration--> the optimum pH. If changes are made, the structure of the enzyme and active site is altered
  • So, the shape of an enzyme changes as the pH changes. They only function within a narrow pH range


  • pH returns to the optimum and the protein resumes its normal shape and is able to catalyse the reaction again
  • However, if the pH change is significant, the structure of an enzme is irreversibly altered- it is denatured. This means the active site is no longer complementary to the substrate 
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pH Graph


  • 1&3 --> the amount of H+ affects the hydrogen and ionic bonds. The interactions between the R groups of the substrate molecule and the R groups of the active site are affected- more difficult for them to interact which means a decrease in rate 
  • 2 --> the optimum pH, the highest rate of reaction 
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Substrate and Enzyme Concentration

  • When the concentration of a substrate is increased, the no. of substrate atoms, molecules or ions in a particular area or volume increases. This means there will be more frequent, successful collisions between subtrate and active site, so there will be an increase in the formation of enzyme-substrate complexes (rate of reaction increases)

Maximum = Vmax --> all the active sites are occupied by substrate particles. No more enzyme-substrate complexes can be formed until products are released from active sites 

  • ^ The only way to increase the rate of reaction in this circumstance would be to add more enzyme or increase the temperature

If the concentration of an enzyme is increased, more active sites are available. This means it becomes a limiting factor again and increasing means the reaction rate will rise until the new Vmax is reached 

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Concentration Graph


  • 1 --> the rate of reaction increases as the substrate concentration increases 
  • 2 --> however, the rate of reaction stops increasing when the Vmax is reached- the rate stays the same and can't increase unless more enzyme is added or the concentration is increased further 
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