Unformatted text preview: Enzymes and Cellular Regulation
What are the factors that regulate the rate at which enzymes catalyze reactions? Why?
Digestive enzymes are protein-based biological catalysts that play important roles in our lives. They help
remove stains from our shirts, turn milk into cheese, and are responsible for turning our dinner into useable fuel for our bodies. Enzymes however do not work well universally. Some are meant to work at high
temperatures, others at low temperatures. They may work best in acidic conditions or neutral conditions.
In this activity we will look at the optimal conditions for two different enzymes. The digestive enzyme
lipase is made in the pancreas and breaks down lipids in the small intestine, while pepsin breaks down
proteins in the stomach. Model 1 – Two Digestive Enzymes lipase
Triglycerides ⎯⎯→ glycerol + fatty acids pepsin
Large polypeptides ⎯⎯→ smaller polypeptides + amino acids Rate of reaction Effect of pH on Enzyme Activity Pepsin (stomach)
Lipase 0 2 4 6 pH 8 10 12 14 1. Name the two enzymes illustrated in Model 1.
Lipase and Pepsin 2. Consider the information provided in the Why? box and in Model 1 about these proteins.
a. In which body organ is pepsin active? stomach b. In which body organ is pancreatic lipase active? small intestine Enzymes and Cellular Regulation 1 3. For each enzyme in Model 1, circle the pH that best represents the environment in which the
enzyme is most active. Pepsin 1.5 8 10.4 Lipase 1.5 8 10.4 4. Compare the rate of the pepsin-catalyzed reaction at pH 1.5 with the rate of the lipase-catalyzed
reaction at pH 1.5. At the pH of 1.5 pepsin maximizes the rate of reaction while Lipase becomes non functional. 5. Compare the rate of the pepsin-catalyzed reaction at pH 8 with the rate of the lipase-catalyzed
reaction at pH 8. At the pH of 8 pepsin becomes non functional while lipase maximizes the rate of reaction. 6. Using your knowledge of protein structure, explain in detail the effect of exposing an enzyme to
a pH outside of its optimal range. Include the effect on both enzyme structure and function. A change in pH can change the weak bonds and interactions, Since the function is based on the shape,
change in shape because denaturation would reduce enzyme activity. 7. At what pH values is lipase likely to be denatured? Justify your answer. 0-4 and 12-14 because they have no activity 8. At what pH values is pepsin likely to be denatured? Justify your answer. 5-14 as the graph shows that the reaction stops meaning there is no activity. 9. In addition to being produced in the pancreas, lipase is also produced in the stomach. Is the
structure of pancreatic lipase the same as gastric (produced in the stomach) lipase? Justify your
reasoning. No, the stomach is acidic and lipase starts to denature in acidic environments. 10. Add a line to the graph in Model 1 that shows a prediction for gastric lipase activity.
11. Antacids work by neutralizing acids, bringing the pH of the stomach to a range of 6–7. What is
the effect of taking an antacid on a person’s ability to digest proteins? The enzymes in the stomach wouldn't work properly in different pH's. 2 POGIL™ Activities for AP* Biology Model 2 – Amylase Rate of Reaction B
Rate of reaction Rate of reaction A 0 20 40
Temperature, °C 80 100
(Substrate concentration always in excess) Rate of reaction C Substrate concentration
(Enzyme concentration constant) 12. Amylase is an enzyme that catalyzes the digestion of carbohydrates. The graphs in Model 2 provide data on several factors that affect the function of amylase in the body.
a. The relationship of which two variables is illustrated in graph A of Model 2?
Rate versus time b. The relationship of which two variables is illustrated in graph B or Model 2? Rate versus enzyme concentration
c. The relationship of which two variables is illustrated in graph C or Model 2?
Rate versus substrate concentration 13. Refer to Model 2.
a. What is the optimum temperature for amylase? approximately 35 to 37 degrees celsius.
b. What is the biological significance of the temperature at which the amylase-catalyzed reaction
is fastest? The significance is that it is the temperatures of the human body. Enzymes and Cellular Regulation 3 14. Predict what causes a decrease in enzyme activity at temperatures above 37 °C. This is caused by a denaturation of the enzyme. 15. A young child runs a fever of 40 °C for 24 hours. Explain what effect this may have on his
digestion. Enzymes will denature due to the body heat being above optimal slowing digestion. If it is present
to long then it could be fatal. 16. Consider the data in graph B of Model 2.
a. Describe the relationship between enzyme concentration and reaction rate. More enzyme results in the increase of the reaction rate b. Propose an explanation for this relationship. More enzymes result in more available active sites 17. Consider the data in graph C of Model 2.
a. What is the relationship between substrate concentration and the reaction rate? As there is more substrate the reaction rate increases b. Propose an explanation for why a maximum reaction rate is reached in graph C. When all active sites are full the reaction rate will level. 18. As a group, develop an analogy for the function of an enzyme that will explain the concentration
graphs in Model 2 (graphs B and C). Enzymes are like construction workers. When the amount of housing projects exceeds the amount
of construction crews the rate of new home development levels. 19. Would the reaction rate on graph B of Model 2 ever reach a maximum level? Justify your answer. The reaction rate would only reach a maximum level only when the enzyme concentration is equal
to the substrate concentration. 4 POGIL™ Activities for AP* Biology Extension Questions
20. Thermophilic bacteria, such as Thermus aquaticus, live in hot springs where the temperature is
greater than 70 °C. Draw a graph similar to graph A in Model 2 representing the optimal temperature of T. aquaticus.
RATE 0 70 deg C 100 deg C 21. DNA polymerase from T. aquaticus (Taq) is used in PCR (polymerase chain reaction). PCR is a
technique where millions of copies of DNA can be made from one original copy. In this method,
the target DNA molecule is subjected to temperatures over 95 °C to make the double-stranded
DNA separate. The temperature is then lowered slightly to allow primers to anneal before the
Taq polymerase catalyzes the reactions to incorporate new nucleotides into the complementary
strands. The cycle is then repeated over and over until there are millions of copies of the
a. Predict why this bacterial polymerase is used instead of a human polymerase. Bacterial polymerase is likely to be used instead of human polymerase because bacterial
polymerase probably works at a faster rate than human polymerase. b. What would happen if you used a human polymerase in a series of PCR reactions? Human polymerase would be denatured. Read This!
The rate of an enzyme-catalyzed reaction can also be affected by the presence of other molecules that can
bind to the enzyme, changing its shape. In some reactions a coenzyme is necessary. This molecule binds
to the protein strands of the enzyme, changing its shape so that is ready to receive the substrate molecule.
Without the coenzyme, the enzyme would not be able to attach to the substrate. Other molecules can
reduce the rate of reaction for enzymes by binding to the protein and either blocking the spot where the
substrate will bind or by making the enzyme’s shape incompatible with the substrate. These molecules are
22. Sketch a graph that shows the relationship between the rate of an enzyme reaction and the
concentration of coenzyme necessary for the enzyme to function properly. Reaction rate coenzyme 23. Add a line to graph C of Model 2 that shows the rate of an enzyme reaction in the presence of
Enzymes and Cellular Regulation 5 ...
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