AP BIOLOGY

Detailed explanation-1: -Cell-Surface Receptors These receptors are also known as transmembrane receptors. These are proteins that are found on the surface of cells and span the plasma membrane. They bind to ligands that cannot themselves pass through the plasma membrane.

Detailed explanation-2: -Whereas hydrophilic signaling molecules travel freely through the bloodstream, but require membrane proteins to influence their target cells. Hydrophobic signaling molecules can pass through membrane, but require water soluble carrier proteins to travel through the blood stream.

Detailed explanation-3: -Structure of representative neurotransmitters. The neurotransmitters are hydrophilic molecules that bind to cell surface receptors. Because the neurotransmitters are hydrophilic molecules, they are unable to cross the plasma membrane of their target cells.

Detailed explanation-4: -The ligand crosses the plasma membrane and binds to the receptor in the cytoplasm. The receptor then moves to the nucleus, where it binds DNA to regulate transcription.