Allosteric Effects – Section 1

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

Correct Answer: A. binding of oxygen to the heme

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)

Correct Answer: D. both (a) and (c)

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

Correct Answer: C. its binding pocket becomes too small to accommodate BPG

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

Correct Answer: B. 1.0 and 2.8

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

Correct Answer: B. 2

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