7.05 Spring 2004 April 23, Recitation #9

Transcription

1 7.05 Spring 004 April 3, 004 Recitation #9 ontact Information TA: Victor Sai Recitation: Friday, 3-4pm, ffice ours: Friday, 4-5pm, -13 Unit 4 Schedule Recitation/Exam Date Topic Recitation #9 Friday, April 3 Pentose Metabolism Recitation #10 Friday, April 30 Fatty, Amino Acid Metabolism Recitation #11 Friday, May 7 Putting it all together Exam Review Saturday, May 17 Lectures 7-36 Exam 4 Thursday, May, 1:30-3:00 Lectures 7-36 Recitation verview Topic Problems 1. Pentose ycle Pathway 1, Quiz. Pentose ycle Mechanisms, [4] 3. Dark Reactions of Photosynthesis 3 Problems 1. (1995 Exam 3 Question 1, 15 points) Indicate the enzymatic reaction sequence that could account for the overall transformation summarized in the equation shown below. There is no need to include structural formulas in your answer. But please name the enzyme that catalyzes each of the proposed reactions. Note that NADP is not involved. 3 Glucose-6-P ATP Ribose-5-P Erythrose-4-P ADP Recitation 9 Page 1 of 6

2 7.05 Spring 004 April 3, 004 ATP ADP 3 Glucose-6-P exose-p 3 Fructose-6-P () P-Fructokinase (1) Fructose-1,6-di P Aldolase (1) (1) Fructose-6-P Glyceraldehyde-3-P Dihydroxyacetone-P (1) Xylulose-5-P Erythrose-4-P Ribulose-5-P Ribose-5-P : Starting Material : Product. (1994 Exam 3 Question, 0 points) Suppose you have an organism that is capable of converting one mol of fructose-6-p and one mol of the sugar whose structure is shown below to one mol of ribulose-5-p and one mol of glucose-6-p. Two enzymes similar to those that operate in the pentose cycle are used in this overall transformation. Please use structural formulas to show the mechanism of this overall conversion. P Recitation 9 Page of 6

3 7.05 Spring 004 April 3, 004 P TA P P Fructose-6-P (6) (5) P Mechanism omitted P Ribulose-5-P (5) P Glucose-6-P (6) Recitation 9 Page 3 of 6

4 7.05 Spring 004 April 3, (1994 Exam 3 Question 1, 30 points) Assume that an organism capable of engaging in photosynthesis has been mutagenized so that lysine resides present at the active sites of enzyme have been replaced by other amino acids (i.e., these enzymes are inactive). During photosynthesis, this organism was observed to be able to carry out the following overall transformation: 3 ATP NADP fructose-6-p 3 ADP Pi NADP ribose-5-p (?) Propose a set of enzymatic reactions, known to occur in organisms capable of photosynthesis, to account for this overall transformation and identify the product (and how much) designated as a question mark in the equation. Glyceraldehyde-3-P Fructose-6-P? = Erythrose-4-P Xylulose-5-P P i NADP Ribulose-5-P ATP 1 1 Ribose-5-P ADP NADP Ribulose-1,5-di P 1,3-di P-Glycerate ADP ATP 3-P-Glycerate Recitation 9 Page 4 of 6

5 7.05 Spring 004 April 3, 004 Practice Problem 4. If Xylulose-5-P is labeled as shown below, where would the label end up in Fructose-6-P in the following conversion? Xylulose-5-P Ribose-5-P Fructose-6-P * P Xylulose-5-P P Fructose-6-P Recitation 9 Page 5 of 6

6 7.05 Spring 004 April 3, 004 * P Xylulose-5-P P Ribose-5-P * P Sedoheptulose-7-P P Glyceraldehyde-3-P TA P Erythrose-4-P * P Fructose-6-P Recitation 9 Page 6 of 6

7 Pentose Metabolism 6 Glucose-6-P 6 NADP Glucose-6-P Dehydrogenase 6 6-P-Gluconolactone Lactonase 6 NADP 6 IRREVERSIBLE IRREVERSIBLE Victor Sai 7.05 Spring P-Gluconate 6-P-Gluconate Dehydrogenase 6 6 NADP 6 NADP IRREVERSIBLE 6 Ribulose-5-P () (4) Ribose-5-P 4 Xyulose-5-P () () Sedoheptulose-7-P Glyceraldehyde-3-P TA Fructose-6-P Erythrose-4-P Xyulose-5-P 1 Dihydroxyacetone-P (1) Glyceraldehyde-3-P Fructose-6-P (1) Aldolase 1 Fructose-1,6-diP ADP P-Fructokinase ATP P i 1 Fructose-6-P Fructose-1,6-diP Phosphatase exose-p exose-p Glucose-6-P

8 Dark Reactions of Photosynthesis (alvin ycle) Light reactions transform light energy into ATP and NADP Dark reacitons use ATP and NADP to assimilate to form fructose P Victor Sai 7.05 Spring ADP 6 ATP P Ribulose-1,5-di P 6 Kinase P Ribulose-5-P 6 6 Ribulose-1,5-di P arboxylase - 1 ATP 1 ADP 1 1 P-Glycerokinase P 3-P-Glycerate P Xylulose-5-P P P 1,3-di P-Glycerate Glyceraldehyde-3P Dehydrogenase 1 P i 1 P 1 NADP 1 1 NADP 5 P Glyceraldehyde-3-P Dihydroxyacetone-P Aldolase P Xylulose-5-P P Sedoheptulose-7-P TA P Erythrose-4-P 5 5 P i P 5 5 Fructose-1,6-di P Phosphatase P P Fructose-6-P Fructose-1,6-di P P Glyceraldehyde-3-P Summary: ATP 1 NADP 1 1 NADP 17 P i 18 ADP Fructose-6-P P Ribose-5-P