Exam 3 Fall 07 KeyMCB181R Dr. Jorstad

Exam 3 Fall 07 KeyMCB181R Dr. Jorstad - MCB 181R Fall 2007...

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MCB 181R, Fall 2007 Instructor: Dr. S. Jorstad Exam III Detailed Key For multiple choice questions (each worth 3 points), bubble all correct answers (there may be more than one); there is a 1 point penalty for incorrect answer choices. For short essays (each worth 5 points): confine your answers to the space provided on the scansheet. Writing outside those margins will adversely affect the machine-scoring of your exam. You may use bulleted points to express yourself, as long as your meaning is clear. 1. The energy in a molecule, such as glucose, a. exists in its covalent bonds. * b. can be captured when the bonds are broken (e.g., by an enzyme) and the energy is transferred to another molecule. * = a description of glycolysis and respiration c. must be released in a slow, step-wise fashion, or much of it will be lost to entropy (e.g., heat and light). * ditto; contrast between respiration and a forest fire (both examples of oxidation of glucose) d. is released in an overall endergonic reaction. exergonic (gives off energy) e. is in its protons, which can be passed from one molecule to the next. somewhat true of electrons, but not protons 2. NAD + a. is a reducing agent. oxidizing agent (pulls electrons off of other molecules) b. can grab electrons from other molecules, and thereby help in extracting the energy in those molecules. * c. is reduced to NADH during glycolysis, pyruvate oxidation, and the citric acid cycle. * (see Fig 7.9 or 7.16 in 7 th edition; 7.7 in 8 th ) d. can be regenerated by the ETC, as it oxidizes NADH. * (Figs. 7.10, 7.12 in 7 th ; 7.11, 7.13 8 th ) e. cannot be regenerated in organisms that live by fermention; they must continuously synthesis new NAD + from scratch. fermentation’s whole purpose is to regenerate NAD+ Short Essay #1: Two of the products of glycolysis are pyruvate and NADH. What happens to each of these molecules in 1) cellular respiration and 2) fermentation? 1) In cellular respiration, pyruvate is completely OXIDIZED (by pyruvate oxidation and the CAC), and NADH is oxidized by the ETC. 2) In fermentation, pyruvate is REDUCED, as NADH hands back its electrons and is thereby oxidized back to NAD+ (NADH is oxidized by pyruvate). 3. The goal of breaking down glucose molecules is to use the energy in the glucose to make ATP—the main form of energy cells use to run endergonic reactions. During this process, for every molecule of glucose,
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a. a net 4 ATPs are synthesized by oxidative phosphorylation during glycolysis. net of 2 ATPs b. 2 ATPs are synthesized by substrate-level phosphorylation during the citric acid cycle. * see Fig 7.8 in both editions c. 4 ATPs are synthesized during pyruvate oxidation. several figures show this is not the case d. 2 ATPs are synthesized during fermentation. (Fig 7.14, 7.15 7 th edition; 7.9, 7.10 8 th ) e. the vast majority of the ATPs synthesized using the energy of a proton gradient. * ~32 of the ~36 4. In the electron transport chain (ETC) of cellular respiration, a. electron carriers are reduced.
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Exam 3 Fall 07 KeyMCB181R Dr. Jorstad - MCB 181R Fall 2007...

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