Enzymes, pH and temperature

• Enzymes become less effective as temperatures increase because the active site of the enzyme changes shape and the molecules become damaged
• Enzymes damaged by heat are said to have been denatured
• The temperature at which an enzyme works best ic called its optimum temperature
• Letter: B

  
• Human enzyme activity peaks at around 40°C
• 36 °C

  
• 60 °C

  
• Up to 36°C, increasing the temperature increases the activity of this enzyme because the substrate particles: move faster and have more energy

  
• Above 36°C, increasing the temperature decreases the activity of this enzyme because the enzyme molecules are: more likely to become denatured

  
• At 70°C, the activity is zero

  
• From the graph, we can say that at 70°C, the molecules of this particular enzyme have all denatured

  
• At -10°C, the activity of the particular enzyme is very small

  
• cold fridge

  
• warm summer's day

  
• deep freeze

  
• cool room

  
• Letter: C

  
• Letter: C

  
• At the wrong pH an enzyme molecule is likely to change its shape
• The shape of an enzyme molecule can be permanently changed by extremes of pH
• As temperature decreases, molecules move slower and so collide less often and have less energy
• As temperature increases, molecules move faster and so collide more often and have more energy
• Reaction rate is less when molecules collide less often and have less energy
• reaction rate is greater when molecules collide more often and have more energy
• when temperature increases, molecules: move faster --so--> collide more often and have more energy --so-->the reaction rate increases
• most enzymes are denatured by boiling