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FINAL2005_Answ - METABOLIC BIOCHEMISTRY Immo E Scheffler...

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METABOLIC BIOCHEMISTRY Winter 2005 Immo E. Scheffler FINAL EXAM All answers are to be written into the Blue Book. Leave the first inside page blank for scoring. There are 16 questions. Make sure that each answer is clearly identified with the question number at the top or left side of the page. Consider the statement on the back of the Blue Book; fill it out and sign it if you want to have your exam returned in the hallway outside of 3234 Bonner Hall. ********************************************************************************* QUESTION 1 [12 points] 1
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a) The mitochondrial electron transport chain contains four protein complexes and two “ mobile carriers”. What are the mobile carriers and in which step(s) are they involved? (A simple schematic diagram with labels is required). [8] The mobile carriers are ubiquinone (coenzyme Q) and cytochrome. Ubiquinone carries electrons from complexes I and II to complex III. Cytochrome c carriers electrons from complex III to complex IV. b) What is a major function of iron-sulfur enters ([Fe-S]) in proteins in the electron transport chain?. [4] A major function of iron-sulfur centers in the subunits of the ETC is to make the proteins capable of conducting electrons. Pure proteins are insulators. Appropriately spaced [Fe-S] centers allow electrons to be passed from one center to the next over a considerable distance (or to ubiquinone). QUESTION 2 [14 points] The following diagram is a schematic representation of the oxygen concentration in a chamber with mitochondria suspended in an appropriate phosphate buffer. Various reagents are added as indicated, with the result that oxygen consumption is either stimulated or arrested. 2
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a) The following is a list of substrates, inhibitors, etc., and you are to match them with the compounds A - E shown in the diagram: 1) rotenone 2) succinate 3) β hydroxybutyrate (to make NADH) 4) ADP 5) antimycin A: ADP B: β -hydroxybutyrate (leads to production of NADH and NADH oxidation by complex I) C: rotenone (inhibitor of complex I) D: succinate (is oxidized by complex II) E: antimycin (an inhibitor of complex III) The alternative is to add β -hydroxybutyrate first, and then ADP b) Instead of ADP one could have used the uncoupler dinitrophenol. Explain briefly. The ADP is added to provide a substrate for complex V and hence a mechanism for protons to return to the mitochondrial matrix; in the absence of ADP an artificial uncoupler like dinitrophenol can be used to provide an alternate path for the return of the protons pumped by the electrontrnasport chain. QUESTION 3 [12 points] a) In substrate level phosphorylations there is a definite stoichiometry between the amount of inorganic phosphate incorporated into a tri-nucleotide (ATP or GTP) and the amount of substrate (e.g. succinyl-CoA) consumed. In oxidative phosphorylation in mitochondria the amount of NADH oxidized and the amount of ATP produced are not related by an integral number. Explain briefly. [8] 3
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An example of substrate level phosphorylation is the following reaction: Succinyl-CoA + P i + GDP succinate + GTP + CoASH (a reaction in the Krebs cycle)
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