Directions: Answers must be in essay form. Outline form is not acceptable. Labeled diagrams may be used to supplement discussion, but in no case will a diagram alone suffice. It is important that you read each question completely before you begin.
An experiment was conducted to measure the reaction rate of the human salivary enzyme α-amylase. Ten mL of a concentrated starch solution and 1.0 mL of α-amylase solution were placed in a test tube. The test tube was inverted several times to mix the solution and then incubated at 25°C. The amount of product (maltose) present was measured every 10 minutes for an hour. The results are given in the table below.
| Time (minutes) | Maltose Concentration (μM) |
|---|---|
| 0 | 0 |
| 10 | 5.1 |
| 20 | 8.6 |
| 30 | 10.4 |
| 40 | 11.1 |
| 50 | 11.2 |
| 60 | 11.5 |
(a) Graph the data on the axes provided and calculate the rate of the reaction for the time period 0 to 30 minutes.
(b) Explain why a change in the reaction rate was observed after 30 minutes.
(c) Draw and label another line on the graph to predict the results if the concentration of α-amylase was doubled. Explain your predicted results.
(d) Identify TWO environmental factors that can change the rate of an enzyme-mediated reaction. Discuss how each of those two factors would affect the reaction rate of an enzyme.
Enolase is an enzyme that catalyzes one reaction in glycolysis in all organisms that carry out this process. The amino acid sequence of enolase is similar but not identical in the organisms. Researchers purified enolase from Saccharomyces cerevisiae, a single-celled eukaryotic yeast that grows best at 37°C and from Chloroflexus aurantiacus, a bacterium that grows best at the much higher temperature of 55°C. The researchers compared the activity of purified enolase from the two organisms by measuring the rate of the reaction in the presence of varying concentrations of substrate and a constant amount of each enzyme at both 37°C and 55°C.
(a) Depending on the organism, the optimal pH for enolase to catalyze its reaction is between 6.5 and 8.0. Describe how a pH below or above this range is likely to affect enolase and its catalytic ability.
(b) Identify the appropriate negative control the researchers most likely used when measuring the reaction rate in the presence of each organism's enolase.
(c) The researchers predict that for any particular concentration of substrate, the C. aurantiacus enolase-catalyzed reaction is more rapid at 55°C than at 37°C. Provide reasoning to justify the researchers' prediction.
The relationship of structure to function is one of the major themes in biology. For the following structure/function pairs, describe the structure and then explain how the function is related to the structure.
Enzyme structure/catalysis