200501M2 - CHEM 237 Midterm 2a March 11, 2005 1. ANSWERS...

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CHEM 237 Midterm 2a March 11, 2005 ANSWERS Note: Exam 2b has the same questions and answers, but the order of the choices is different. 1. Which statement about Hb is true ? a. release of one O 2 from a saturated Hb tetramer increases the likelihood of another O 2 being released b. O 2 and Bohr protons bind at the same site on the Hb molecule. c. Hb binds CO with about the same affinity as it binds O 2 . d. when O 2 binds to a subunit of Hb, the O 2 replaces the distal HisE8 as a ligand to the heme iron. ANSWER: A. Release of one O 2 from a saturated Hb tetramer affects the release of other O 2 molcules by increasing the likelihood of another O 2 being released. Bohr protons and O 2 do not bind to the same site; CO bind to Hb with much greater affinity than O 2 ; and His E8 does not ligand the Fe in any form of non-mutant Hb (its His F8). 2. BPG has what effect on the affinity of Hb for O 2 ? a. BPG binds at the center of the Hb tetramer and increases the affinity of Hb for O 2 . b. BPG reduces the affinity of fetal Hb by binding to the fetal Hb tetramer more strongly than to adult Hb. c. the binding of BPG to Hb reduces the affinity of Hb for O 2 by shifting the O 2 binding curve toward the Y-axis. d. BPG reduces the affinity of Hb for O 2 by stabilizing the T-state of Hb. ANSWER: D. BPG binds to the T-state, thereby stabilizing that state. BPG does bind to the center of Hb, but it decreases the affinity; BPG binds more weakly to HbF than to HbA; BPG does reduce the affinity of Hb to O 2 , but the curve is shifted away from the Y-axis. 3. Which statement is true about the Bohr effect? a. Because of the Bohr effect, R-state Hb binds more H + than the T-state b. HbA binds O 2 more tightly at lower pH. c. Fe +2 ions are released from Hb when the pH is lowered to pH 6. d. HbA affinity for O 2 is higher at high CO 2 concentrations. e. The Bohr effect explains why more O 2 is released in an exercising muscle than in a muscle at rest. ANSWER: E. Exercising muscle is releasing more CO 2 than non-exercising muscle, and this will lower the pH of the blood, which shifts the O 2 binding curve and results in the release of more O2 into the blood. Bohr protons bind to the T-state , not the R-state ; increase in pH results in a shift of the curve to lower affinity; Fe ++ ions are not released from Hb under normal conditions; as CO 2 goes up, acidity goes down, and affinity goes down with it. 4. Which statement is true about sickle cell Hb (HbS)? a. HbS is a result of a mutation of Glu6 α to a Val. b. The mutant Val residue binds to other T-state HbS tetramers and causes aggregation of the HbS molecules c. This really is only a problem in the lungs were the R-state prodominates; HbS in the R-state aggregates and cause the red blood cells to become sickle-shaped. d.
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This note was uploaded on 12/02/2010 for the course CHEM 233 taught by Professor Daub during the Fall '09 term at Waterloo.

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200501M2 - CHEM 237 Midterm 2a March 11, 2005 1. ANSWERS...

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