midterm2006.answ - METABOLIC BIOCHEMISTRY Immo E. Scheffler...

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METABOLIC BIOCHEMISTRY Winter 2006 Immo E. Scheffler MIDTERM EXAM All answers are to be written into the Blue Book. Leave the first inside page blank for scoring. There are 10 questions. Make sure that each answer is clearly identified with the question number at the top or left side of the page. Useful Information: Avogadro's number: 6.02 x 10 23 molecules / mole 1 Faraday = 96,494 Coulomb / mole = 96,494 Joules / Volt / mole Gas constant (R) = 8.31 Joules K -1 mol -1 = 1.987 cal K -1 mol -1 = 0.082 liter atm K -1 mol -1 1 calorie = 4.184 Joules ********************************************************************************** QUESTION 1 a) ( 8 points )The following are generic names of several enzymes. Describe two of these with a specific example (the reaction catalyzed by each enzyme) and identify the nature of the reaction as group transfer, oxidation reduction, etc. Kinase Dehydrogenase Mutase Phosphatase Isomerase Dehydratase a kinase transfers a phosphate group from ATP to a small molecule or to a protein - a group transfer ATP + Glu ADP + Glu-6P a dehydrogenase removes hydrogen from a substrate, i.e oxidizes the substrate, while NAD+ is oxidized - an oxidation/reduction reaction Pyruvate + NADH lactate + NAD + a mutase changes on structural isomer to another - an isomerization Glu-1P Glu-6P a phosphatase hydrolyzes a phosphomonoester bond - a hydrolysis (H 2 O is one of the substrates) phosphorylase a + H 2 O phosphorylase b + inorganic phosphate (P i ) an isomerase changes one structural isomer to another - an isomerization Glu-6P Fru-6p a dehydratase removes water from a substrate, typically forming a double bond between adjacent carbons - a dehydration; the enzyme you have encountered is the enolase. 2-phosphoglycerate PEP + H 2 O
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b) ( 8 points ) You have learned about the formation of a Schiff base in enzymatic catalysis. Illustrate the formation of a Schiff base using the specific example of the aldolase reaction encountered in glycolysis (Structural formulae required) you should have the structures for the reaction: Fru-1,6bisphosphate dihydroxyacetone phosphate and glyceraldehyde-3 phosphate Structure on the right of the diagram is the intermediate Schiff base. QUESTION 2 A kinetic scheme for an enzyme catalyzed reaction has been formulated by Michaelis and Menten. It makes an assumption about the steady state concentration of an enzyme-substrate intermediate. An expression for the initial rate (v) of the reaction can be derived as follows: k 2 [E total ] [S] V o = -------------------------- (k 2 +k -1 )/k 1 + [S] a ) ( 4 points ) show the reaction sequence formulated by M&M and assign rate constants to the elementary steps k 1 k 2 S + E <==> E-S ==> P + E k -1 b ) ( 1 point ) what is the expression for K m
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k -1 + k 2 Km = -------------- k 1 c) ( 2 points ) what is the expression for v
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midterm2006.answ - METABOLIC BIOCHEMISTRY Immo E. Scheffler...

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