Download Activity 6

CHEM 121 Name: Activity 6: Rates of Reaction, Equilibrium, and Le Chatelier’s Principle Refer to p.784 and 785 in your textbook for the glycolysis reactions 1. In glycolysis, phosphohexose isomerase catalyzes the equilibrium reaction of glucose 6-­‐phosphate to fructose 6-­‐phosphate (Reaction 2). If we reproduced the reaction in lab, how would the concentrations of the two sugar phosphates compare to a control sample in which no enzyme was present? 2. During cellular activity, fructose 6-­‐phosphate is converted irreversibly to fructose 1,6-­‐phosphate, causing the fructose 6-­‐phosphate concentration to drop (Reaction 3). Based on Le Chatelier’s principle, what would be the result of this disturbance to the equilibrium discussed in Question 1? 3. Glucose 6-­‐phosphate is itself produced by an equilibrium reaction of glucose catalyzed by hexokinase (Reaction 1). The equilibrium constant is large for this reaction. Which predominates, glucose or glucose 6-­‐phosphate? 4. How will this equilibrium (Question3, Reaction 1) be affected by the result in Question 2? 5. After eating, blood glucose levels are high, and as a result, cell glucose concentrations also increase. What effect would this have on the equilibrium described in Question 3 (Reaction1)? CHEM 121 Name: 6. If a person is sedentary after eating, so less ATP is used by their cells and it accumulates, how will that affect the equilibrium reaction described in Question 3 (Reaction 1). In that reaction, ATP is a co-­‐reactant. 7. Under the same conditions as Question 5 but for the reaction in Question 2 (Reaction 3), which is irreversible and has ATP as a co-­‐reactant, what will be the effect on the concentration of fructose 6-­‐phosphate? 8. How will the equilibrium in Question 1 (Reaction 2) be affected by the result of Question 7? 9. How will the equilibrium in Question 3 (Reaction 1) be affected by the result of question 8? 10. The results of Questions 6 and 9 are due to the same cause and affect the same reaction. Are the results additive or opposite in their nature? CHEM 121 Name: 11. In addition to the effects in Questions 6 and 9, there is another effect of ATP on this reaction. It is an inhibitor of the enzyme hexookinase which is the catalyst for the reaction. Is this effect in the same direction or opposite in direction to the effects in Question 10? 12. The enzyme for Reaction 3, phosphofructokinase is also inhibited by ATP. Under the conditions in Question 5, what will happen to fructose 6-­‐
phosphate concentration? 13. How will the result from Question 12 affect glucose 6-­‐phosphate concentration? 14. How will the result from Question 13 affect glucose concentration? 15. What you are seeing in these answers is the feedback mechanism for metabolism. Three enzymes (hexokinase, phosphofructokinase, and pyruvate kinase) control the rate of glycolysis. What happens to the rate of glycolysis when ATP is low? 16. What happens to cell and blood glucose levels when the rate of glycolysis is high? CHEM 121 Name: 17. The hormone insulin is produced when blood glucose levels are high, such as immediately after eating. It causes the storage of glucose in polymer form, glycogen. Would the situation in Question 16 result in glycogen formation? 18. The hormone glucagon is produced when glucose levels are low. It causes the liver to convert glycogen to glucose and release it to the bloodstream. Would the situation in Question 16 result in the breakdown of glycogen in the liver? 19. The hormones epinephrine and norepinephrine behave similarly to glucagon, but act primarily in muscle tissue. Would the situation in Question 16 result in the breakdown of glycogen in muscle tissue? 20. Gluconeogenesis literally means formation of new sugar. In this process, glucose is formed from non-­‐carbohydrate sources: lactate built up from exercise, amino acid metabolism, and glycerol from fats. For each hormone mentioned in Questions 17 through 19, predict its affect on gluconeogenesis (promote it or inhibit it) in the situation in the Question 16 result (the same situation as for Questions 17-­‐19).