7.05 Spring 2004 April 9, Recitation #7

Transcription

1 7.0 Spring 00 April 9, 00 Recitation #7 ontact Information TA: Victor Sai Recitation: Friday, -pm, - -mail: sai@mit.edu ffice ours: Friday, -pm, - Unit Schedule Recitation/xam Date Topics Recitation #7 Friday, April 9 arbohydrates, nzymatic Reactions Recitation #8 Friday, April Sugar Metabolism, Pathway Game xam Review Monday, April 9, 7pm, xam Wednesday, April, Walker 9- Recitation verview Topic Problems. arbohydrates. Ring Structures,,. Isomerase and pimerase. Aldolase,, [], Quiz Problems. (99 xam Question, 0 points) Draw the structure of the following compound: α-d-galactopyranosyl-( )-α-d-ribofuranosyl-( )-β-d-mannopyranoside Recitation 7 Page of

2 7.0 Spring 00 April 9, 00. (99 xam Question, 0 points) Assume that an organism can enzymatically convert glucose--p to mannose--p. Show how this might be done enzymatically without the participation of an epimerase. int: Two enzymes are involved, one of which is hexose-p isomerase. P Glucose--P P Mannose--P P Glucose--P : P P P Fructose--P P Mannose--P : P P P Recitation 7 Page of

3 7.0 Spring 00 April 9, 00. Assume the hypothetical compound below can be converted to two -carbon compounds by the action of a single enzyme of the type described in class. What would the products be? You need not show the mechanism of this transformation.. (99 xam Question, points) Assume that the compound whose structure is shown below can be made (in the presence of a single enzyme) from two other compounds. Write the structures of these two compounds and shown how they could be used to form the product. Please use structural formulas, indicate mechanisms (electron shifts), and include any proposed enzyme-bound intermediates. int: the enzyme is of a type that was discussed in class and does not need a coenzyme for activity to be expressed. - Recitation 7 Page of

4 7.0 Spring 00 April 9, N Aldolase N N - N - N - - N N - - Recitation 7 Page of

5 7.0 Spring 00 April 9, 00 Practice Problem. (998 xam Question, 0 points) Show how the compound shown below could be produced from lactate and another three-carbon compound in the presence of a series of enzymes that are involved in gluconeogenesis. Write the structure of the other three-carbon compound. Assume the presence of a sufficient amount of nucleoside triphosphates. Give the mechanisms (with the use of structural formulas) for those enzymatic reactions in which enzyme-bound covalent intermediates are produced. For any other reactions it is sufficient to give the names of the reactants and the products. Note that the enzyme aldolase is not specific with regard to substrate utilized. P P Recitation 7 Page of

6 7.0 Spring 00 April 9, 00 The structure of the other -carbon compound is: P The reaction would proceed as follows: NAD NAD Lactate Pyruvate -Biotin- - ADP P i GDP GTP PP AA -Biotin ATP - -P-Glycerate -P-Glycerate ATP ADP,-di P-Glycerate S- P S P NAD Glyceraldehyde--P Dehydrogenase P NAD P NAD N P N Aldolase P Isomerase P S- NAD S NAD NAD P P N P N P N P N P P P P Recitation 7 Page of

7 arbohydrates Victor Sai 7.0 Spring 00. Drawing arbohydrates: First draw each carbohydrate, then draw the linkages α/β configuration: used for ring structures. α denotes the group of the original carbonyl carbon pointing down, β denotes the group pointing up D denotes the orientation of the group on the chiral carbon farthest from the carbonyl if the group points to the right, it is D; if it points to the left, it is L. All carbohydrates in 7.0 are of D configuration.. Ring Structures group pointing up in ring structures corresponds to pointing left in Fisher projections Similarly, down in ring structures corresponds to right in Fisher projections Formation of ring: pening of ring:. nzymes involved in Transformations ISMRAS: converts one isomer to another (e.g., phosphoglucoisomerase, triose phosphate isomerase) R R isomerase R R Page of

8 PIMRAS: changes the configuration of the group on a chiral carbon R R epimerase R R ALDLAS: catalyzes aldol condensation aldolase Reverse Aldol Forward Aldol KINAS: adds a phosphate group from ATP (e.g. hexokinase, galactose kinase, pyruvate kinase) PSPATAS: removes a phosphate group (e.g., glucose--p phosphatase) DYDRGNAS: removes hydrogens by oxidation. Usually requires NAD or FAD as co-factors/co-substrates. (e.g. glyceraldehyde--p dehydrogenase) MUTAS: transfers a phosphate group to a different position (e.g. phosphoglycerate mutase, glucose--p mutase). NLAS: converts = groups to alcohol. No change in oxidation state. Functions in reverse direction in glycolysis. Page of

9 arbohydrates -- ommon Sugars ncountered in Recitation andout. Allen & S. hen Glucose Galactose Mannose Fructose Ribose Ribulose Xylulose Note: All sugars are shown in α D configuration. glucopyranose galactopyranose mannopyranose fructofuranose ribofuranose ribulofuranose xylulofuranose Maltose α-d-glucopyranosyl-(->)- (α or β) D-glucopyranose Lactose β-d-galactopyranosyl-(->)- (α or β)-d-glucopyranose Sucrose α-d-glucopyranosyl-(->)- β-d-fructofuranoside *notice fructose is inverted!!

10 Aldolase. Allen & S. hen 7.0 Recitation andout Spring 00 Mechanism N (99%) from Lys residue in active site of enzyme Summary of reaction in glycolysis P α β P Fructose-,-diP Dihydroxyacetone-P (DAP) Aldolase Glyceraldehyde--P (Gly--P) P P * This oxygen is replaced with an oxygen from water * N (%) P.. N P - N P.. Schiff Base.. N P P Schiff Base N P P - N P.. P P * N DAP P Gly--P General verall Reaction** (like reverse aldol condensation) Aldolase * * This oxygen is replaced with an oxygen from water ** Aldolase is fairly non-specific with regard to substrate α β