Consider the Binding of a Transcription Regulatory Protein (A) to a Promoter

Multiple Choice

Consider the binding of a transcription regulatory protein (A) to a promoter DNA (p) according to the following scheme.

A + p?A:p
At steady state, which of the following formulae correctly yields the bound promoter fraction, i.e. [A:p]/([A:p] + [p]) ? The association constant is designated as K.

A) [A]/(K + [A])
B) K[A]/(1 + K[A])
C) K[A]/(K + [A])
D) [A]/(1 + K[A])