pH Effects on Enzyme Activity

Background: Cells carry out many chemical processes. These reactions would occur too slowly if it were not for special proteins called enzymes. Enzymes are protein molecules that speed up chemical reactions. Enzymes are important for the breakdown and building of organic molecules.

In this experiment, you will observe the enzyme peroxidase (catalase) speed up the breakdown of hydrogen peroxide into water and oxygen gas. This is an important reaction in living organisms as hydrogen peroxide is a waste product which can poison the cell if it is not broken down.

peroxidase

2H2O2 ------2H2O + O2

Objectives:

  1. To determine at what pH peroxidase functions the best.

Question:

Hypothesis:

Data Table 1: Height of Oxygen Bubbles at Different pHs

(Construct a data table to show all necessary data clearly)

Analysis:

(What type of data analysis would be best to answer the question? )

Figure 1: Graph of Height of Bubbles Plotted as a Function of pH

(construct graph of height of bubbles (y axis) and

pH (x axis)

Analysis Questions:

  1. What is the name of the enzyme in this experiment?
  2. What is the substrate the enzyme is acting on in this experiment?
  3. What is causing the bubbles to appear in the test tubes?
  4. What does it mean if no bubbles appear?
  5. Explain why peroxidase is an important enzyme for living organisms.
  6. Normal human body temperature is about 37ºC. According to your results, can you predict whether this would be an optimum temperature for peroxidase or not?
  7. Which pH seems to be worse for peroxidase? Acidic or basic? Explain.
  8. Explain how you would run an experiment in order to determine how the amount of enzyme available would affect the rate at which the reactants form products.

Results/Conclusions:

Refer back to objective. Support with data.

Sources of error

Improvements

Procedure for Peroxidase Experiment

pH variable

(Be sure to wear your goggles !!)

  1. Label test tubes #1 -5.

TT#1 = enzyme mixture, H2O2, water, pH 7

TT#2 = enzyme mixture, H2O2, HCl, pH 1

TT#3 = enzyme mixture, H2O2, vinegar, pH 3

TT#4 = enzyme mixture, H2O2, NaOH, pH 13

TT#5 = enzyme mixture, H2O2, baking soda solution, pH 9

  1. Place one pipette full of enzyme mixture into each of the test tubes.
  1. Take TT#1 and add 10 drops of water. Next add 5 drops of hydrogen peroxide. Wait 3 minutes and measure the height of the bubbles in millimeters. Record in your data table.
  1. Take TT#2 and add 10 drops of HCl. Next add 5 drops of hydrogen peroxide. Wait 3 minutes and measure the height of the bubbles in millimeters. Record in your data table.
  1. Take TT#3 and add 10 drops of vinegar. Next add 5 drops of hydrogen peroxide. Wait 3 minutes and measure the height of the bubbles in millimeters. Record in your data table.
  1. Take TT#4 and add 10 drops of NaOH. Next add 5 drops of hydrogen peroxide. Wait 3 minutes and measure the height of the bubbles in millimeters. Record in your data table.
  1. Take TT#5 and add 10 drops of baking soda solution. Next add 5 drops of hydrogen peroxide. Wait 3 minutes and measure the height of the bubbles in millimeters. Record in your data table.
  1. Carefully pour contents of test tubes down the sink while running the water. Rinse each test tube and clean using the test tube brush and soap. Return test tubes to the rack upside down to dry.