Final answer:
Localized regions of plasma membranes with cholesterol and proteins for cell signaling are cell-surface receptors, integral to processes like signal transduction, maintaining membrane fluidity, and forming lipid rafts for cell signaling.
Step-by-step explanation:
Localized regions of plasma membranes that contain cholesterol and proteins involved in cell signaling are known as cell-surface receptors. These are complex, integral proteins, often referred to as transmembrane receptors, that can bind external signaling molecules or ligands. They span the plasma membrane and are involved in the process of signal transduction, converting an external signal to one that can be understood and responded to inside the cell. The plasma membrane itself is a phospholipid bilayer that contains various embedded proteins and cholesterol which maintains fluidity and assists in signaling functions. Cholesterol, in particular, is crucial as it impacts the membrane's flexibility and is involved in the formation of lipid rafts, areas that are important for cell signaling. In addition to being embedded in the cell membrane, cholesterol is also found in the brain and myelin sheath of nerve cells and serves as a precursor to vitamin D and various steroid hormones.