A Researcher Discovered a Small Protein Secreted by the Pituitary

question 150

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.

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