BC351 quiz 8

A mutation in an allosteric protein causes it (the allosteric protein) to experience a decrease in its affinity for a positive heterotropic modulator. Based upon this which of the following is true? A. The mutation will cause the equilibrium between the T and R-state to shift toward the T-state (relative to the unmutated protein) at non-saturating conditions of modulator. B. The mutation will not disrupt the equilibrium between the T and R-state. C. The mutation will lead to an increase in the affinity of the protein for its ligand. D. The mutation will not change the affinity of the protein for its ligand. E. A) and C).

A. The mutation will cause the equilibrium between the T and R-state to shift toward the T-state (relative to the unmutated protein) at non-saturating conditions of modulator.

An allosteric protein demonstrates a decrease in its Kd for molecule Y as the concentration of molecule X increases. Based on this information which of the following statements is true? A. X is a homotropic positive modulator. B. X is a heterotropic positive modulator. C. X is a homotropic negative modulator. D. X is a heterotropic negative modulator.

B. X is a heterotropic positive modulator.

Modulator

Binds reversibly to the protein and induces conformational changes in proteins.

Ligand

Binds reversibly to the protein but does not necessarily induce a conformational change.

An allosteric protein demonstrates a decrease in its Kd for molecule Y as the concentration of molecule X increases. Based on this information which of the following statements is true? A). Molecule X binds at the same site of the protein that molecule Y binds. B. Molecule X will bind to and stabilize the T-state. C. Molecule X will bind to and stabilize the R-state. D. Molecule Y cannot induce a conformational change in the protein when molecule X is present. E. C) and D).

C. Molecule X will bind to and stabilize the R-state.

Hemoglobin: A. binds oxygen with a higher affinity than myoglobin due to the presence of four heme groups vs. only one in myoglobin. B. binds oxygen with a lower affinity than myoglobin due to the presence of four heme groups vs. only one in myoglobin. C. binds to oxygen with a lower affinity than myoglobin due to the presences of the T-state that is absent in myoglobin. D. binds to oxygen with a higher affinity than myoglobin due to the presences of the R-state that is absent in myoglobin. E. A) and D).

C. binds to oxygen with a lower affinity than myoglobin due to the presences of the T-state that is absent in myoglobin.

Cooperativity

Modulation between R and T states is accomplished at the ligand binding site.

Allostery

Modulation between R and T states is accomplished at the regulatory site.