A Researcher Discovered a Small Protein Secreted by the Pituitary

Multiple Choice

A researcher discovered a small protein secreted by the pituitary that functions as a growth factor to stimulate cell division in mouse skin cells.The skin cells of mice that have a mutation in a particular gene do not respond to this growth factor.When the researcher isolated and sequenced the gene, she found that it coded for a protein kinase.Which statement best explains this?

A) The signal transduction pathway has at least one step in which the signal is transmitted by the activation of a protein via phosphorylation.
B) Phosphorylation of a protein is necessary in order to shut down or inhibit the signal transduction pathway stimulated by the growth factor.
C) The growth factor binds to a cell membrane receptor that has an inactive phosphorylated state and a dephosphorylated active state.
D) The growth factor must be phosphorylated before it can bind to the cell membrane receptor to initiate the signal transduction pathway.
E) The cell membrane receptor must be phosphorylated by a neighboring skin cell before it can bind to the growth factor to initiate the signal transduction pathway.