What happen once intercellular signals reach the inside of the cell using some type of receptor

A. The signal stops

B. The signal produces a protein

C. The signal is transferred to the cytoplasm

D. Intercellular communication takes over

east cells communicate with one another for mating by secreting a few kinds of small peptides. In contrast, cells in higher animals communicate by means of hundreds of kinds of signal molecules. These include proteins, small peptides, amino acids, nucleotides, steroids, retinoids, fatty acid derivatives, and even dissolved gases such as nitric oxide and carbon monoxide. Most of these signal molecules are secreted from the signaling cell into the extracellular space by exocytosis (discussed in Chapter 13). Others are released by diffusion through the plasma membrane, and some are exposed to the extracellular space while remaining tightly bound to the signaling cell's surface.

Regardless of the nature of the signal, the target cell responds by means of a specific proteincalled a receptor, which specifically binds the signal molecule and then initiates a response in the target cell. The extracellular signal molecules often act at very low concentrations (typically ≤ 10-8 M), and the receptors that recognize them usually bind them with high affinity (affinity constant Kα ≥ 108 liters/mole; see Figure 3-44). In most cases, these receptors are transmembrane proteins on the target cell surface. When they bind an extracellular signal molecule (a ligand), they become activated and generate a cascade of intracellular signals that alter the behavior of the cell. In other cases, the receptors are inside the target cell, and the signal molecule has to enter the cell to activate them: this requires that the signal molecules be sufficiently small and hydrophobic to diffuse across the plasma membrane