Factors effecting enzyme-controlled reactions

• How does pH affect enzyme-controlled reactions?

  • A change in pH refers to a change in the hydrogen ion concentration. More hydrogen is present in a low pH environment and fewer hydrogen ions are present in high pH (alkaline) environments
  • In an acidic/alkaline environment, there is an excess of H+/OH- ions. These will interfere with the hydrogen and ionic bonds in the tertiary structure of the enzyme. This changes the shape of the active site so that it is no longer complementary to the substrate (denatured).
• Rate of Enzyme Activity in relation to pH levels:

  
• Buffer: Resists changes in pH by accepting or donating electrons
• How does temperature affect enzyme-controlled reactions?

  • The optimum temperature is the temperature which enzymes work best. It is the temperature at which the enzyme has its maximum rate of reaction.
  • Increasing the temperature increases the kinetic energy of the particles. As a result, the frequency of collisions between the substrates and active sites increases. This means that enzyme-substrate complexes can form more quickly thereby increasing the rate of the reaction.
• • Below 0C temp is too low for induced fit to occur (frozen crystalline structure)
  • As kinetic energy increases, there are more successful collisions between enzymes and substrates (more ESCs)
  • As we increase past the optimum there is too much kinetic energy, causing the hydrogen and ionic bonds within the tertiary structure to break, changing the shape of the active site, and denaturing it.
  • The maximum rate of reaction is known as the Vmax

  
• The temperature coefficient of Q10:

  • For chemical relations in a test tube Q10 is approximately 2, which means for every 10C rise in temp the rate of reaction is doubled

  
• Effect of changing substrate concentration:

  • As substrate is added and its concentration increases, the rate of reaction increases.
  • This is because more enzyme-substrate (ES) complexes can form. As a result, more product molecules are formed.
  • Substrate concentration is limiting the reaction, because, as it increases, the rate of reaction increases
  • Substrate concentration is the limiting factor. As the concentration of substrate is increased even further, the reaction will reach its maximum rate.
• Substrate concentration Graph:

  1. As substrate concentration increases so does the rate of reaction as there are more ESCs, meaning more successful collisions. Substrate concentration becomes limiting
  2. No further increases in the rate of reaction as all active sites become occupied. Enzymes are all working at Vman. Enzyme concentration becomes limiting

  
• The effects of enzyme concentration on the rate of reaction:

  • More enzymes mean more available active sites for the breakdown of the substrate
  • More ESCs, more successful collisions
  • Enzymes become limiting
  • As it continues no further increases as all substrate is catalysed meaning there is not enough substrate
  • Substrate becomes limiting