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Protein Function.docx

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University of Alberta
Nat Kavetal

Protein Function 1. A protein reversibly binds two different ligands, Y and Z. If the Kd for ligand Y binding is twice the Kd for ligand Z binding, then: A. The binding affinity for Y is higher than that for Z. B. The binding affinity for Y is lower than that for Z. C. The binding affinity for Y and Z is the same. D. No statement can be made regarding their relative affinities. 2. Which of the following classifications describes the effect of H + ions on hemoglobin? A. Heteroallosteric, possitive effector. B. Homoallosteric, negative effector. C. Heteroallosteric, negative effector. D. Homoallosteric, possitive effector. 3. What changes occur when hemoglobin switches from the deoxy (T) form to the oxy (R) form? A. The distal histidine moves and drags helix E. B. The Fe ion moves into the plane of the heme. C. The central cavity becomes larger. D. The iron in heme is oxidized from Fe to Fe . 3+ 4. Fetal hemoglobin binds BPG with higher affinity than maternal hemoglobin A. True B. False 5. Myoglobin and hemoglobin are both oxygen‐binding proteins but have very different physiological roles. Which two of the following are the most important factors that contribute to their different functions? 1. Myoglobin is a monomeric protein, whereas hemoglobin is a tetrameric protein. 2. Hemoglobin binds BPG which stabilizes the deoxy (T) state. 3. Myoglobin has a sigmoidal oxygen‐binding curve whereas hemoglobin has a hyperbolic oxygen‐binding curve. 4. The primary structure of myoglobin is completely different from that of hemoglobin. A. 1 and 2 B. 1 and 3 C. 1 and 4 D. 2 and 3 E. 3 and 4 6. In hemoglobin, replacing the proximal histidine (His F8) with serine would be a conservative substitution. A. True B. False 7. If curve 3 represents the binding of oxygen to normal hemoglobin, which curve would represent the binding behaviour of hemoglobin in the presence of an allosteric effector that interacts with the "R" state? A. 1 B. 2 C. 3 D. 4 E. None of the curves 8. Which of the following statements is (are) correct about curves 1‐4 in the attached figure? If curve 3 describes oxygen binding to hemoglobin at pH 7.2, curve 2 describes oxygen binding to hemoglobin at pH 7.4. A. Curve 1 represents oxygen binding to hemoglobin in the absence of BPG. B. If curve 3 describes oxygen binding to adult hemoglobin, curve 2 describes oxygen binding to fetal hemoglobin. C. If curve 3 describes oxygen binding to hemoglobin at pH 7.2, curve 2 describes oxygen binding to hemoglobin at pH 7.4. Furthermore, Curve 1 represents O 2binding to hemoglobin in the absence of BPG. D. All of the statements are true. 9. Which statement is TRUE regarding the interactions involving hemoglobin and BPG? A. BPG enables hemoglobin to bind oxygen. B. BPG prevents premature release of oxygen. C. BPG binding is sensitive to pH. D. BPG interacts specifically with a large central cavity in the "R" state.The graph above shows several oxygen binding curves that were obtained for hemoglobin under different experimental conditions. 10. Which of the following is TRUE about prosthetic groups? A. Prosthetic groups are inorganic. B. Prosthetic groups are bound and released by the protein as needed. C. Prosthetic groups are an integral part of the tertiary structure of the protein. D. Prosthetic gro
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