Ex2_comments_2006 - BioG 101 Cornell University EXAM 2...

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BioG 101 Cornell University Exam 2 comments 1 Nov 11, 2006 EXAM 2 COMMENTS Average Score = 43.37 pts out of a possible 58 points (= 74.78%). Standard Deviation = 7.36 points (12.69%). Total Points on this Exam: 58. This prelim will count for about 23% of your final grade in BioG 101. Correct answers (including alternate answers accepted in red ). Oral and written comments on the exam. About 40 students attended the oral review of the exam, and there were 89 e-mails about the exam questions. Once again, I am immensely impressed by the clarity and logic behind many of these queries and comments, and as you will see in the comments below, I have accepted alternative answers in some cases, but not all. When I was persuaded that there was a valid case for misinterpretation of the question, or an alternative that I had not previously considered I have also accepted alternative answers. In all cases, I appreciate the time you took to give feedback, since it is the feedback like this that ultimately leads to better teaching, less confusing exams, and better understanding. I thank all students who took the time to provide feedback. Comment on the grade distribution. As I said in lecture, the significantly higher mean on this examination compared to the first was impressive to me, as this test is traditionally the most difficult of the semester. Improved study habits, familiarity with the style of the course, and a re-dedication to the web quizzes and reading no doubt all contributed to the improvement in scores overall. I am deeply gratified to see the trend.
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BioG 101 Cornell University Exam 2 comments 2 Nov 11, 2006 E1 E2 E3 E4 E5 threonine Æ C1 Æ C2 Æ C3 Æ C4 Æ isoleucine Comments on selected questions. 1) Most students realized that the first law of thermodynamics requires that all living things obtain energy from their environment, whether it be from sunlight, from thermal vents, or from pre-formed organic molecules of other living things. Choice C, picked by some, is incorrect since organisms must constantly obtain new energy in order to maintain biological structures and continue to metabolize. 3) FADH2 is the best choice because both FADH2 and NADH are reduced dinucleotides, both are electron carriers used for temporary carriers of electrons in biochemical metabolism, and because both contain the nucleotide adenine. 6) Five reactions convert threonine to isoleucine as follows: Where C’s are intermediate compounds and E’s are enzymes. To say that the synthesis of isoleucine is regulated implies that the amount produced is controlled by negative feedback. Ideally the end product should control the rate of the very first reaction – by inhibition, not activation, of enzyme E1. Thus, as isoleucine levels increase, it shuts down the synthesis of C1 by inhibiting enzyme E1. All subsequent intermediate products are also shut down by the lack of C1. There are two ways for the inhibition to work, either by allosteric inhibition of the enzyme E1 or by competitive inhibition of E1. Allosteric inhibition works best because the enzyme is inhibited regardless of how much
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Ex2_comments_2006 - BioG 101 Cornell University EXAM 2...

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