Investigating Enzymatic Reactions

• Required Practical: the effect of pH on the rate of reaction of Amylase
• Iodine is used to test for the prescence of starch.
• What is the independent variable?


  The pH of the buffer solution.
• What is the dependent variable for the required practical?


  Time taken for the reaction to complete (time for the starch to be digested by the amylase).
• Below is the method for the practical:

  
• Rate is a measure of how much something changes over time.
• Example:

  The enzyme catalase the breakdown of hdrogen peroxide into water and oxygen. During an investigation into the activity of catalase, 24cm^3 of oxygen was released in 50 seconds. Calculate the rate of reaction. Write your answer in cm^3.

  Amount of product formed = change = 24cm^3.

  rate of reaction = change/time = 24/50 = 0.48cm^3/s
• Example:

  At pH6, the time taken for amylase to break down all of the starch in a solution was 90 seconds. So the rate of the reaction = 1000/90 = 11s^-1.

  For this type of question, use the formula rate = 1000/time
• Exam question:

  An enzyme-controlled reaction was carried out at pH4. After two minutes, 36cm^3 of product has been released. Calculate the rate of rection in cm^3/s.


  2 minutes = 2 x 60 = 120 seconds

  36/120 = 0.3cm^3/s
• Enzymes lower the activation energy needed for a chemical reaction to occur.
• Starch, proteins and fats are large molecules that cannot yet be absorbed for nutrients.
• The "big" moleculas can't pass through the digestive system, so digestive enzymes have to break them down.
• Give two examples of smaller digestive molecules.

  Amino acids, sugars, glycerol and fatty acids.
• Why is it best to break down these molecules?

  They can easily pass through the walls of the digestive system, therefore being absorbed into the bloodstream.
• What happens to enzymes in extremes of temperature?


  The enzyme will denature.
• What does it mean when an enzyme denatures?


  The bonds holding together the 3D shape of the active site break.
• What happens to the active site of an enzyme when it denatures?


  The active shape will deform.
• What is the consequence of an enzyme's active site deforming?


  The substrate will not be able to fit into the active site anymore.