19 - Friday, October 7, 2011 Lecture 19 Announcements: 1....

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Friday, October 7, 2011 Lecture 19 Announcements : 1. Quiz 5 results: A 20.4 sd 5.6 B 21.5 sd 6.1 C 22.6 sd 6.0 2. PyMOL Reviews will not take place until after Fall Break: Sun 10/16 3 – 5PM in Carpenter Hall Red Computer Lab; and Tu 10/18 4:30 - 6PM in Malott 251 3. Midterm exam Th 10/20 at 7:30PM, room TBA Make-up exam: Sat 10/22, 11AM – 1:30PM ( MUST e-mail Prof with conflict before Fall Break!! ). Room TBA 4. How to study for the midterm exam: Discussion on Friday 10/14 at 1:25PM in Comstock B108 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. Wednesday's lecture: Ways to regulate enzymes: 1. control enzyme concentration: synthesis is controlled by controlling mRNA synthesis. splicing, and degradation; and by controlling translation on the ribosome. Protein destruction by hydrolysis is also under control. 2. control enzyme activity (for such regulated enzymes). Allosteric control via feedback inhibition, example of ATCase. p. 145 ATCase IV structure is C 6 r 6 . This shorthand means that the enzyme has six catalytic subunits, and six regulatory subunits. The catalytic subunits C are organized into two catalytic C 3 trimers. The IV structure can be described as either R-state or T-state. The R-state has catalytic sites that bind the substrate very well. Isolated catalytic trimers are enzymatically very active . (Note the similarity to the relation between Mb, a high- affinity oxygen binding protein, and Hb in the T-state, a low affinity oxygen binding protein. Think about what is meant by T = tense state vs R = relaxed state). The T-state has almost no catalytic activity, and binds substrate only very weakly. In the T state, the two catalytic trimers bind each other, and block and distort all of the active sites. This is the stable IV structure of T-state ATCase. The regulatory, or “r” subunits can force the C 3 trimers apart, which is the R-state . The R-state is also induced by cooperative binding of substrates aspartate and carbamoyl phosphate, and by binding ATP at the allosteric site .
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The allosteric effectors ATP and CTP bind to the regulatory subunits, not to the catalytic subunits. When CTP binds, the catalytic trimers bind each other well, forming the stable T-state. When ATP binds, the regulatory subunits undergo a large change, rotating and
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This note was uploaded on 01/01/2012 for the course BIOMG 3310 taught by Professor Feigenson during the Fall '11 term at Cornell University (Engineering School).

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19 - Friday, October 7, 2011 Lecture 19 Announcements: 1....

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