redox_metabolism_review_key

redox_metabolism_review_key - Bis2A Redox and metabolism...

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Bis2A: Redox and metabolism review sheet This is a review sheet that should be useful before our first midterm. 1. Biologists often use the term energy source as a synonym for “electron donor”. Why? In a “downhill” redox reaction, a molecule (electron donor) transfers one or more electrons to another molecule (electron acceptor) and drops in potential energy during the process. This change in energy can be harvested during metabolic redox reactions to do work (drive a reaction, or pump a proton) making the donor a source for energy. 2. Your instructors claim that the evolution of an oxygen atmosphere paved the way for increasingly efficient cellular respiration and higher growth rates in organisms. Explain how this could be the case. Since it is such a strong oxidizing agent, relative to other molecules available in the atmosphere before its emergence, oxygen becomes a lower ‘sink’ of potential energy. This allows for a larger change in free energy upon oxidation of an energy source, thus providing more energy for growth.
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If you find the problem below baffling, please consult the document “Reduction potential”, available on the Britt BIS2A MyUCDavis website. Below are columns (side by side) that show oxidation-reduction couples arranged from the strongest reductants (negative reduction potentials) at the top to the strongest oxidants (positive reductive potentials) at the bottom. As electrons are donated from the top of the tower, they can be “caught” by acceptors at various levels. The farther the electrons fall before they are caught (i.e., the greater the difference in reduction potential between the electron donor and acceptor) the more energy is released. (ΔE 0 ’ is proportional to ΔG°’; that is ΔG°’ = - nF ΔE 0 ’, where n is the number of electrons, and F is Faraday’s constant, 96.48 kJ/V). Couple (half reaction) E 0 ’ (V) Couple (half reaction) E 0 ’ (V) CO 2 / Glucose -0.43 (24 e-) CO 2 / Glucose -0.43 (24 e-) 2 H+ / H 2 -0.42 (2 e-) 2 H+ / H 2 -0.42 (2 e-) CO 2 / methanol -0.38 (6 e-) CO 2 / methanol -0.38 (6 e-) NAD + / NADH (or NADP + / NADPH) -0.32 (2 e-) NAD + / NADH (or NADP + / NADPH) -0.32 (2 e-) CO 2 / Acetate -0.28 (8 e-) CO 2 / Acetate -0.28 (8 e-) S 0 / H 2 S -0.28 (2e-) S 0 / H 2 S -0.28 (2e-) SO 4 2- / H 2 S -0.22 (8 e-) SO 4 2- / H 2 S -0.22 (8 e-) Pyruvate / lactate -0.19 (2e-) Pyruvate / lactate -0.19 (2e-) Cytochrome b ox/red +0.035 (1 e-) Cytochrome b ox/red +0.035 (1 e-) Ubiquinone ox/red +0.11 (2 e-) Ubiquinone ox/red +0.11 (2 e-) Cytchrome c ox/red +0.25 (1 e-) Cytchrome c ox/red +0.25 (1 e-) Cytochrome a ox/red +0.39 (1 e-) Cytochrome a ox/red +0.39 (1 e-) NO 3 - / NO 2 - +0.42 (2 e-) NO 3 - / NO 2 - +0.42 (2 e-) NO 3 - / N 2 +0.74 (5 e-) NO 3 - / N 2 +0.74 (5 e-) Fe 3+ / Fe 2+ +0.76 (1 e-) Fe 3+ / Fe 2+ +0.76 (1 e-) ½ O 2 / ½ H 2 O +0.82 (2 e-) ½ O 2 / H 2 O +0.82 (2 e-) 3. Draw arrows linking the two half-reactions involved in each of the reactions below. a. H 2 + NO 3 - NO 2 - + H 2 O b. NADH + pyruvate lactate + NAD + c. glucose + 6O 2 6CO 2 + 6H 2 O d. H 2 + ½ O 2 H 2 O 4. Now rank those reactions by the amount of energy released (from most energy released, to least) C > D > A > B 5. The bacterium Streptococcus mutans is abundant in the mouths of Western European and North American children and is a prominent cause of cavities. The organism is virtually absent from the mouths of children in East Africa, where tooth decay is rare.
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