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Biochemistry Objective Questions { Allosteric Effects }



1. The conformational changes from the T to the R state is initiated by
A. binding of oxygen to the heme
B. movement of the proximal histidine towards the heme
C. movement of the F-helix, which contains the proximal His
D. reorganization of protein-protein contacts between the individual subunits
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2. An allosteric activator
A. increases the binding affinity
B. decreases the binding affinity
C. stabilizes the R state of the protein
D. both (a) and (c)
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3. Bisphosphoglycerate (BPG) cannot bind to the oxygenated R state of hemoglobin because
A. it is displaced from the heme by oxygen
B. it is displaced from the heme by movement of the proximal histidine
C. its binding pocket becomes too small to accommodate BPG
D. BPG binds to the R state with the same affinity as the T state
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4. The Hill coefficient (nH) for myoglobin and hemoglobin are respectively
A. 2.8 and 1.0
B. 1.0 and 2.8
C. 1.2 and 4.5
D. 4.5 and 1.2
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5.  When protein binds two ligands in a non-cooperative manner, then the x-intercept of the Scatchard Plot is
A. 1
B. 2
C. not defined
D. none of the above
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6. O2 binding to hemoglobin results in
A. 100-fold higher affinity for the last O2 bound than for the first
B. extensive protein conformational change
C. both (a) and (b)
D. 100-fold lower affinity for the last O2 bound than for the first
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7. In hemoglobin, allosteric effects occur
A. only in humans
B. for maintaining Fe in the Fe2+ state
C. to minimize oxygen delivery to the tissues
D. to maximize oxygen delivery to the tissues
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