Consider four small molecules, a–d, which have the following binding affinities for a specific enzyme (these numbers are the equilibrium constants kd for the dissociation of the enzyme/molecule complex). which binds most tightly to the enzyme? which binds least tightly?

a) 4.5 μm

b) 13 nm

c) 8.2 pm

d) 6.9 mm

Binding affinity measures the strength of the interaction between a molecule to its ligand; it is expressed in terms of the equilibrium dissociation constant; and the higher value of this constant, the more weaker the binding between the molecule and the ligand is. On the other hand, small constans means that the interaction is tight. So "C" binds most tightly to the enzyme and "D" binds least tightly.

1. a)c-14 has two more protons

2. d)they have different numbers of protons, neutrons, and valence electrons; they are all gases at room temperature.

3. c) iron and nickel.