AP BIOLOGY

Detailed explanation-1: -Second messengers are molecules that relay signals received at receptors on the cell surface-such as the arrival of protein hormones, growth factors, etc.-to target molecules in the cytosol and/or nucleus.

Detailed explanation-2: -Second messengers provide a direct connection between signaling molecules such as neurotransmitters, cytokines, and growth factors and changes in gene expression that are ultimately responsible for the proliferation, differentiation, and maturation of nerve cells.

Detailed explanation-3: -The activation of multiple target enzymes by a single second messenger molecule further amplifies the signal. Second messengers are not only produced in response to extracellular stimuli, but also in response to stimuli from within the cell.

Detailed explanation-4: -Hence, these bind to the receptors present on the plasma membrane forming a hormone receptor complex. This binding generates other molecules like Ca++, cAMP etc. which act as secondary messengers. These secondary messengers drive a cascade of biochemical reactions and physiological changes in the target cell.

Detailed explanation-5: -Water-soluble hormones are not lipid-soluble. Thus, they will not be able to diffuse across the cell membrane. This limitation requires the first messenger to activate a second messenger which will create a connection of the hormone to prompt cellular response.