Chem 454, Spring Exam I R, the ideal gas law constant = x 10-3 kj/mol = x 10-3 kcal/mol

Transcription

1 Name Chem 454, Spring Exam I R, the ideal gas law constant = x 10-3 kj/mol = x 10-3 kcal/mol 1. Metabolism can be divided into two processes: catabolism and anabolism. a. Define metabolism, catabolism and anabolism. b. Describe how the oxidation state of carbon-based molecules is related to catabolism and anabolism. c. Describe how phosphoryl transfer potential is related to catabolism and anabolism. 2. In glycolysis, there is a reaction in which oxidation of a carbon-based molecule is coupled to the production of a phosphate with a high phosphoryl transfer potential. a. Write the net reaction equation for this reaction. b. The product of this reaction contains two phosphate groups, the one which has a high phosphoryl transfer potential, and the other which does not. Explain the structural reasons for this difference. 1

2 c. There are two amino acid side chains that are involved in the catalytic mechanism for this reaction. Identify each and describe the role that each plays in the reaction. d. This reaction involves a coenzyme; identify this coenzyme and describe two roles it has in the mechanism for the reaction. e. Catalysts increase the rate of a reaction by lowering the activation free energy for a reaction. Describe how the enzyme that catalyzes this reaction lowers the activation energy for the reaction. 3. Describe what an activated carrier is. a. Describe what is carried by each of the following carrier molecules. Identify, by name, a reaction in glycolysis, gluconeogenesis, or the citric acid cycle that each participates in. i) ADP ii) FAD iii) NAD + iv) Coenzyme A v) Lipoamide vi) Biotin b. Which of these carriers contain a remnant of the ancient RNA world, a time when RNA served as both catalysts and information-storage molecules. 2

3 4. The DG ' for the phosphoglucose isomerase reaction glycolysis is +1.7 kj/mol, whereas in vivo, in cells, DG' is 2.5 kj/mol. a. Using structural formulas, write the balanced chemical equation for this reaction b. The one free energy difference indicates a favorable reaction, whereas the other does not. Explain the difference. c. If under standard conditions of temperature and pressure, the cellular concentration of glucose 6-phosphate is 5 mm, what is the concentration of the product of this reaction? d. If under standard conditions of temperature and pressure, the equilibrium concentration of glucose 6-phosphate is 5 mm, what is the concentration of the product of this reaction? e. Propose a mechanism for this reaction based on the mechanism for triose phosphate isomerase. 3

4 5. When the hormone glucagon binds to receptors on liver cells it leads to the activation of the enzyme protein kinase A (PKA), which in turn leads to the phosphorylation of the bifunctional enzyme phophofructokinase 2 (PFK2)/fructose bisphosphatase 2 (FBPase2). a. Under what conditions is glucagon released into the bloodstream? b. What effect does the phosphorylation by PKA have on the activity of the bifunctional enzyme? c. What effect does this in turn have on glycolysis? d. If glucagon is the primary messenger in this signal transduction pathway, what is the second messenger? e. Describe the points in the signal transduction pathway, from glucagon binding to the activation of PKA, where signal amplification occurs. 6. Describe the purpose of the citric acid cycle a. Using structural formulas, write the balanced chemical equation for the two reactions were CO 2 is produced. 4

5 b. Using structural formulas, write the chemical equation for a reaction in the citric acid cycle that is an example of an isomerization reaction. c. Using structural formulas, write the chemical equation for a reaction in the citric acid cycle that is an example of an addition (lyase) reaction. d. Using structural formulas, write the chemical equation for the reaction in which GTP is produced from GDP and P i. 5