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.

b.final

substituting a hydrogen atom with a halogen in a hydrocarbon:

- the single bond remains single. a is wrong.

- the bond with hydrogen is as strong as with a halogen. c is wrong

- a hydrocarbon is saturated if there is no double bond. we do not know that so d is wrong.

- carbon will always have four valence electrons. e is wrong.

by elimination, the correct answer is b. the boiling point of the new compound increases.