Enzyme Lab - Questions

Catalase

Living cells produce hydrogen peroxide,  H2O2, as a waste product, but if left alone it would poison the cells.  The cells produce an enzyme, catalase, to detoxify the hydrogen peroxide:

    2  H2O2       catalase     >    2 H2O   +   O2

Catalase is found in most organisms, but the catalase varies – variants have evolved which best fit into certain conditions of pH and temperature.

Part One – Temperature Effects

We are going to make up a solution with catalase in it from liver samples, with the liver coming from chicken or cows – in both cases, homeothermic, temperature-stable organisms with temperatures somewhat close to the human standard of 37^o C.   We are going to test enzyme activity at four different temperatures.  Make predictions based upon what you know of enzymes and of this enzyme in particular.  Predict how the reaction rates should compare:  faster, slower, nonexistent.

Part Two – Substrate Concentration

For this test, we will increase the amount of substrate being added to a constant amount of enzyme, then measure how quickly the reaction takes place.  Over five trials of increased substrate, we should see a Michaelis-Menten pattern in the results.

What is the substrate in these reactions?

If we get the Michaelis-Menten pattern, what should happen?

DATA SHEET – PART 1

Do these results confirm your original predictions?

If they don’t, why do you think that is?

DATA SHEET – PART 2

Does there seem to be a Michaelis-Menten pattern in the results?

If so, how do the results show such a pattern?  If not, what should the pattern have shown?

Questions –

1.      If everyone produces different catalase solutions, why are the tests reliable?


 

2.      Some versions of this lab have students record the highest point reached by the bubbles.  Why do you think this is or is not a proper measurement of reaction rate?

 

3.      In the substrate concentration test, every tube had 1mL of catalase solution.  Why was that critically important?

4.      Catalase has four hemes, iron-containing prosthetic groups.  Give a way that this might enhance its activity.

5.      One important feature of catalase activity is that it releases oxygen as paired atoms, O2.  Why is this better than releasing oxygen atoms singly?