Refer to the Graphs Below

Multiple Choice

Refer to the graphs below. Human cells taken from the large intestine were cultured in dishes and divided into control and experimental groups.Control cells were incubated for 1 hour in a buffered solution, while experimental cells were incubated for 1 hour in a buffered solution that also contained 10 M dibutyryl cyclic AMP (db-cAMP) .Dibutyryl cyclic AMP has biological activity similar to that of cyclic AMP (cAMP) but readily diffuses through the cell membrane.Following the incubations, researchers isolated a protein known to act as a transcription factor from the cells.They measured both the protein quantity (graph A) and the amount of phosphorylation of the protein (graph B) .Which statement is consistent with these results?

A) cAMP does not function as a second messenger in the signal transduction pathway that stimulates this transcription factor.
B) cAMP's role in this signal transduction pathway is to stimulate expression of the transcription factor's gene.
C) cAMP's role in this signal transduction pathway is to stimulate phosphorylation of the transcription factor.
D) Phosphorylation of the transcription factor occurs upstream of cAMP synthesis in this signal transduction pathway.
E) The transcription factor is activated by cAMP through an increase in its gene expression and through a chemical step in which the factor becomes phosphorylated.