Homework 3 11F KEY

Homework 3 11F KEY - Metabolic Biochemistry Fall Quarter...

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Metabolic Biochemistry Name_______________ Fall Quarter 2011 Homework 3 (40 pts.) Section______________ 1) (7 pts.) Use the diagram below to answer the following questions about the reaction mechanism for the pyruvate dehydrogenase complex. a. On hydroxyethyl-TPP, circle the part of the hydroxyl ethyl group that gets oxidized in the following step—be as accurate as you can. b. Which enzyme catalyzes the oxidation step in part (a) above? E 1 or E 2 or E 3 c. Draw the structure of the chemical group that is attached to lipoyllysine here. d. Is this form of lipoyllysine oxidized or reduced? reduced e. Write in both forms of the missing electron carrier in the box (not the structure). f. Is this form of lipoyllysine oxidized or reduced? Oxidized g. This kind substrate transfer through multiple enzyme subunits and their coenzymes is known as Substrate Channeling CH 3 C O NAD + NADH
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2) (4 pts.) A test electrode contains a solution of ubiquinone, with both the fully oxidized and fully reduced forms, at 1 M concentration each. A circuit is formed from this electrode using a KCl solution salt bridge with a standard hydrogen electrode (25°C, 1 ATM H 2 , 1 M H + ). When this circuit is complete, a current of electrons pass to the ubiquinone test cell at +0.045 volts. a. What is the standard reduction potential (E°’) of ubiquinone? 0.045 volts The description given above is the definition of reduction potential. The reduction potential of a compound is defined relative to the standard hydrogen electrode. b. Which has a higher standard reduction potential, ubiquinone or oxygen? Oxygen. 3) (7 pts.) Complex 3 of the electron transport chain catalyzes the transfer of electrons from ubiquinone to an electron carrier that carries the electrons to complex 4. a. What is the name of the electron carrier that receives electrons from complex 3? Cytochrome C b. Describe what this electron carrier is composed of. What specifically holds the electrons? This is protein (single polypeptide) that contains a heme prosthetic group. c. Where is this electron carrier located in the mitochondria? (Be specific.) Soluble in the Intermembrane Space (or IMS) d. Write a balanced chemical equation for the transfer of electrons, catalyzed by complex 3, from ubiquinone to complex 4. QH 2 + 2cytC ox Q + 2cytC red + 2H + (Or ½ QH 2 + cytC ox ½Q + cytC red + H + ) e. Calculate the standard free energy change for the equation you wrote for part d above, using G’° = -nF E’°. The reduction potential for ubiquinone is 0.045 V and the reduction potential for the electron carrier that receives the electrons is 0.254 V.
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This note was uploaded on 11/27/2011 for the course BIBC 102 taught by Professor Price during the Fall '02 term at UCSD.

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Homework 3 11F KEY - Metabolic Biochemistry Fall Quarter...

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