Lecture 19 - Friday, October 6, 2006 Lecture 19...

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Friday, October 6, 2006 Lecture 19 Announcements : 1. Quiz 5 results: A 20.0 B 20.8 C 20.3 2. RasMol Reviews: Sun 10/15 1 – 3PM in Carpenter Hall Red Computer Lab; and Tu 10/17 4:30 - 5:30PM in Racker Room, Biotech ground floor 3. Midterm exam: Kennedy Auditorium or Warren B45, Thursday 10/19, 7:30 - 10PM Make-up exam: Sat 10/21, 3M – 5:30PM ( e-mail Prof with conflict ). Room TBA 4. How to study for the midterm exam: a. Last year’s exam is on our web site (Blackboard). Don’t look yet at the key! Take the exam after you are 3/4 done with studying, and only then look at the key. b. Be able to answer every question from the first 5 quizzes. c. Understand every word from every lecture. d. Use the text as a supplement. 5. Internships abroad in health, education, social work: Th 10/12 4:45PM in Goldwin Smith Kaugmann Auditorium. Wednesday's lecture: Chymotrypsin step-by-step mechanism Today's lecture: Note about the small curved arrows that indicate electron flow: think of these electron flows as leading to the next intermediate . p. 132 For the family of enzymes known as the Serine proteases, here is the overall reaction equation for the catalyzed reaction: E + S ES ES' ES'' ES''' EP 2 E + P 2 P 1 The rate of enhancement over the uncatalyzed hydrolysis of peptide is about 10 10 . What if we mutate either Ser195 or His57? You might imagine that catalysis would be completely ruined. Indeed, the rate enhancement drops to about 10 5 . This is a big drop of about 100,000-fold, but there is still impressive catalytic power left! Catalytic
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power still comes from the binding, hence stabilization, of the tetrahedral transition state. A summary of some key catalytic features of chymotrypsin: Ser195-O: binds to the peptide carbonyl C (nucleophilic attack) Ð Peptide NH of Ser195 and Gly193 H-bond to the O - of the tetrahedral transition state (and tetrahedral intermediates) Enzyme shape fits the tetrahedral intermediate, thereby especially lowering TS free energy.
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This note was uploaded on 02/13/2008 for the course BIOBM 3310 taught by Professor Feigenson,gw during the Fall '07 term at Cornell.

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Lecture 19 - Friday, October 6, 2006 Lecture 19...

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