What happens to the shape of protein molecules when they are heated?
Questions For Further Thought
1. Predict what would happen to a living organism exposed to temperatures that fall outside the optimal range for its enzymes.
2. List some familiar adaptations animals have to reduce the effects of temperature extremes on their many vital, enzyme-catalyzed reactions. a. b. c. d.
3. In general, the rates of chemical reactions double for every 10 degree (Celsius) increase in temperature. At the molecular level, what changes account for slower reaction rates of enzyme- catalyzed reactions at high temperatures? (Hint: enzymes are three-dimensional protein molecules. What happens to the shape of protein molecules when they are heated? How would this change the vital “active site” of the enzyme?) — Why are enzyme catalyzed reactions also slower at low temperatures? (Hint: In a liquid or gas, what happens to the motion of molecules as they cool? Why would this affect the rate at which enzyme and substrate molecules collide and react?)
4. The binding of enzymes with their substrates is most efficient under certain (so called “optimal”) pH conditions. An enzyme molecule’s 3-dimensional shape is maintained by hydrogen bonds and other chemical bonds sensitive to pH. How might extremes in pH change the efficiency of the enzyme?
5. Human cells and body fluids contain hundreds of natural buffer systems that keep pH at or very near optimal levels. Potato cells and human cells are both living and so have thousands of biochemical reactions in common. Given your results for catecholase, what value of pH is most likely to be found inside human cells?
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LAB REPORT At your next Discussion class, hand-in a lab report to your TA. You and your partner can submit identical cover pages and data tables, but your introduction and discussion must be written by you, in your own words. (1) Cover page: including the title of the experiment (in this case, use “Effects of environmental factors on the rate of enzyme catalyzed reactions”), your name, the date, your discussion leader’s name, and the number of your discussion section. Also include the names of all your partners and their discussion section leaders. (2) Introduction: State your two hypotheses about the effects of temperature and acidity (pH) on the rate of this enzyme catalyzed reaction. Explain why each hypothesis makes sense to you. State the prediction you generated from these hypotheses and describe (in general terms) how you tested them. You don’t need to detail the methods (because they are already in the lab guide), but you do need to say enough to show you understand the experiment; e.g., which substance is the enzyme, which is the substrate, and why your Spec 20 data can be used to compare the rate of the reaction under different conditions. (3) Results: On a separate page, summarize your data from the tables and graphs on pages 10 and 13. (4) Discussion: In 1- 2 pages, explain why each of your two curves is shaped the way it is. Explain why your curves went up or down at low, intermediate, and/or high temperatures and pH’s. Compare your actual curves to the theoretically-expected shapes for these curves. You should include any relevant parts of your answers to the questions raised in the “Analysis and Discussion” and “Questions for Further Thought” sections of the lab guide.