2. Protein A has a binding site for ligand X with a Kd of 10-6M. Protein B has a binding site for ligand X with a Kd of 10-9M. Which protein has a higher affinity for ligand X

Protein B has a higher affinity for ligand C than protein A

Explanation:

Binding affinity is a measure of the strength of the bonds or interactions between a single biomolecule or receptor to its ligand. A ligand is usually a small molecule that binds to a specific receptor.

The receptor is usually a large molecule that contains a specific site for the binding of ligand.

Binding affinity is usually measured by the equilibrium dissociation constant (KD). The equilibrium dissociation constant KD is a ratio of the dissociation and the association of ligand to the receptor. The value of KD is used to evaluate and compare the strengths of bimolecular interactions.  The larger the KD value, the more weakly the target molecule and ligand are attracted to and bind to one another.

The higher the dissociation constant (KD), the weaker the affinity is between the interacting molecules, whereas, the smaller the KD value, the greater the binding affinity of the ligand for its target.

Protein B has a KD value of 10⁻⁹ M while Protein A has a KD of 10⁻⁶ M.

Ration of KD of protein B to protein A = 10⁻⁹ M/10⁻⁶ M = 10⁻³

Therefore, protein B has a KD value which is 1000 times smaller than the KD of protein A.

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