Advanced Placement (AP) Biology Practice Exam

What type of molecule is typically involved in second messenger signaling?

1. A lipid-based hormone

2. A small protein

3. A water-soluble ion or molecule

4. A large relay protein

The correct answer is: A water-soluble ion or molecule

Second messenger signaling typically involves water-soluble ions or molecules, which play a crucial role in transmitting signals within cells after the activation of cell surface receptors. These second messengers, such as cyclic AMP (cAMP), calcium ions, and inositol trisphosphate (IP3), help to amplify the signal from the first messenger – usually a hormone or neurotransmitter that binds to a receptor on the cell membrane. When the receptor is activated, it often triggers changes in the concentrations of these water-soluble second messengers inside the cell, allowing for a rapid and effective response to the original signal. This process allows for a cascade of physiological responses, integrating and amplifying the signal throughout the cell and potentially to other parts of the organism. Lipid-based hormones, small proteins, and large relay proteins do not typically act as second messengers in this context, as they usually function in different mechanisms of signaling and transduction. Lipid-based hormones often pass through cell membranes and interact with intracellular receptors, while small proteins may have roles in other signaling pathways. Large relay proteins can be involved in signal transduction but do not serve as second messengers themselves.