[Campbell Biology P.274] According to the provided text, which of the following statements b... | Practice Question
According to the provided text, which of the following statements best defines or describes a "second messenger" in cell signaling pathways?
A: A large protein that binds to the cell surface receptor and initiates a phosphorylation cascade.
B: A small, nonprotein component of signal transduction pathways that relays signals from receptors.
C: A molecule, such as ATP, that provides direct energy for signal transduction.
D: The initial signaling molecule (ligand) that binds to the receptor on the cell's exterior.
E: Any molecule that directly activates a cellular response without being involved in a cascade.
Explanation
The text explicitly states that scientists use the term "second messenger" for "all small, nonprotein components of signal transduction pathways" that relay signals from receptors. IP3 and DAG are given as examples of such messengers.