ALLOSTERIC EFFECTS Multiple Choice Questions :-
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
Answer: A
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)
Answer: D
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
Answer: C
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
Answer: B
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
Answer: B
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
Answer: C
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
Answer: D
8. A protein that binds two ligands in a non-cooperative manner will show
A. a sigmodial binding curve
B. a hyperbolic binding curve
C. a linear Scatchard Plot
D. both (b) and (c)
Answer: D
9. Small molecules affect hemoglobin (Hb) by
A. decreasing Hb affinity for O2
B. increasing [H+]
C. increasing Hb affinity for O2
D. increasing [H+] and decreasing Hb affinity for O2
Answer: D
10. A protein that shows infinite cooperative for binding of n ligands will
A. show a Hill coefficient (nH) of 0.0
B. only be found in either the unliganded form or the fully liganded form
C. show a Hill coefficient (nH) of n
D. both (b) and (c)
Answer: D
ALLOSTERIC EFFECTS Objective type Questions with Answers
11. The specificity of a ligand binding site on a protein is based on
A. the absence of competing ligands
B. the amino acid residues lining the binding site
C. the presence of hydrating water molecules
D. the opposite chirality of the binding ligand
Answer: B