Which of the following statements is true regarding hydrophilic ligands?

• A. They enter the cytosol freely
• B. They bind to intracellular receptors
• C. They are located on the cell membrane
• D. They produce quick, long-lasting effects

Answer: (C)

For hydrophilic ligands, the statement that they are located on the cell membrane is accurate. Hydrophilic ligands, which include many hormones and neurotransmitters, cannot easily cross the lipid bilayer of the cell membrane due to their polar nature. Instead, they rely on binding to receptors on the exterior of the cell membrane. This binding initiates internal cellular signals, typically through second messenger systems, rather than directly entering the cytosol.

In contrast, hydrophilic ligands do not enter the cytosol freely nor do they bind to intracellular receptors, which is characteristic of hydrophobic ligands that can cross the membrane and interact with receptors inside the cell. Regarding the effects produced by hydrophilic ligands, they tend to elicit quick responses, but these are generally not long-lasting as they usually trigger immediate signaling pathways that can quickly modify cellular processes but may not result in sustained changes without ongoing signaling.