Enzymes and Cellular Regulation

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 ±±A glycerol + fatty acids pepsin Large polypeptides ±±A smaller polypeptides + amino acids Rate of reaction Effect of pH on Enzyme Activity Pepsin (stomach) Lipase 0 2 4 6 8 10 12 14 pH 1. Name the two enzymes illustrated in Model 1. Pepsin and Lipase 2. Consider the information provided in the Why? box and in Model 1 about these proteins. a. In which body organ is pepsin active? the stomach b. In which body organ is pancreatic lipase active?the small intestines 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 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. The pepsin is at 3 while the lipase is a 2 5. Compare the rate of the pepsin-catalyzed reaction at pH 8 with the rate of the lipase-catalyzed reaction at pH 8. The pepsin is at 5 while the lipase is at 4.5 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. Exposing a enzyme to PH changes the form of the model so the attachment cant attach its self to the enzyme to break down food, therefore the enzyme becomes inactive. 7. At what pH values is lipase likely to be denatured? Justify your answer. 12, on the graph the lipase is at 0 when the pH is 12 so that means the enzyme is denatured once the pH level gets to 12. 8. At what pH values is pepsin likely to be denatured? Justify your answer. 5, on the graph the pepsin is at 0 when the pH is 5 so that means the enzyme is denatured once the pH level gets to 5. 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. Yes, they are the same enzyme working in two places. 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? Some of the enzymes would be denatured, for example the pepsin becomes denatured at pH 5 so bringing the pH to 6-7 would denature the pepsin enzyme in your stomach. 2 Model 2 – Amylase Rate of Reaction B Rate of reaction Rate of reaction A 0 20 40 60 Temperature, °C 80 100 Enzyme concentration (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? Temperature and the rate of the reaction b. The relationship of which two variables is illustrated in graph B or Model 2? Enzyme concentration and the rate of the reaction c. The relationship of which two variables is illustrated in graph C or Model 2? Substrate concentration and the rate of the reaction 13. Refer to Model 2. a. What is the optimum temperature for amylase? 40 c b. What is the biological significance of the temperature at which the amylase-catalyzed reaction is fastest? Depending on the temperature it can denature the protein or make it act faster. Enzymes and Cellular Regulation 3 The colder the slower the reaction His digestion would be increased since 40 c is the optimal temperature for the enzyme amylase As the enzymes increase so does the reaction rate. The more the enzymes equals the more products so it would make the reaction faster. As the substrate concentration goes up the reaction rate shoots up and then settles to a steady rate as the substrate goes up. The enzyme only needs so much substrate not a continus flow so the reaction just stayed the same as the substrate went up. its like eating food, the more you have the fuller you get as the outcome if eating so much food. No the line stopped before the graph ended Extension Questions 20. Thermophilic bacteria, such as Thermus aquaticus, live in hot springs where t greater then 70 °C. Draw a graph similar to graph A in Model 2 representing perature of T. aquaticus. 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 target DNA. a. Predict why this bacterial polymerase is used instead of a human polymerase. The live in hot conditions and bacterial polymerase in known to survive the extreme while human polymerase would have a low heat tolerance. b. What would happen if you used a human polymerase in a series of PCR reactions? When the PCR reacts its at a high temperature so the human polymerase would not be able to sustain these temperatures. 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 called inhibitors. 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. 23. Add a line to graph C of Model 2 that shows the rate of an enzyme reaction in the presence of inhibitor molecules. Enzymes and Cellular Regulation 5