Question

Homework for lab 4: Complete exercise 4 page 76-77-78 (question 6 only for page 78). Design your own experiment to examine the effect of pH on reaction rate. Material: • Solution of pH 5, pH 7 and pH 9 • Catechol • Potato extract (that's the enzyme) Water (optional) . . . Answer those questions (p77-78) what is your hypothesis What are your dependant and independant variables What are your controls • Briefly explain your experiment below • Design a table that describe your experimental conditions (similar than the table 1 p75). Enter the volume in ml (milliliters) of each solution you add. You can add more column and rows to the table if you need to. Tubes Potato extract (= enzyme) Catechol (=substrate) 1 2 3 4 for the blank tube . What do you predict to be the outcome of your experiment? Explain why you expect that outcome

Answer 1

• Hypothesis - pH could affect the rate of a reaction within a neutral to basic range (7-9 pH), below or above which the enzyme denatures.

• Dependent variable - Rate of reaction as it will change with the change in the pH.

Independent variable - pH of the reaction, as it is independent of the changes in the reaction rate.

• Controls given:

1. Positive control - In this, the product is already present which should give the same number of bubbles as the enzyme-catalyzed reaction. It helps to know if the reaction has taken place efficiently.

2. Negative control - No substrate i.e. Catechol is added to it so there should be no bubbles obtained from it.

3. No-enzyme control - It is similar to the negative control only but in this substrate catechol is present but no potato extract so, it should not display any enzyme activity.

• Experiment in brief:

1. Same amount of potato extract is added in the three separate tubes.

2. Given three different pH solutions of pH 5, 7 and 9 are added to it.

3. Same amount of substrate (Catechol) is added to each of the tube.

4. Enzyme activity is represented by counting the no. of bubbles obtained, due to the catalase acting on the Catechol to form oxygen and water.

• Tubes	Water (in ml)	Potato extract (in ml)	Catechol (= substrate)
  1 (pH = 5)	-	5	5
  2 (pH = 7)	-	5	5
  3 (pH = 9)	-	5	5
  4 (for blank)	5	-	5

• Expected outcome: Enzyme activity should be maximum at pH 7 and stay the same at 9. But at pH 5, no enzyme activity is expected to be present as the enzyme gets denatured at this pH.

• It would have been more informative to use pH higher than 10 or 11 to estimate the enzyme activity to know if there's a pH limit at which the enzyme activity decreases.