Differentiate between different types of signals

There are two kinds of communication in the world of living cells. Communication between cells is called intercellular signaling, and communication within a cell is called intracellular signaling. An easy way to remember the distinction is by understanding the Latin origin of the prefixes: inter– means “between” (for example, intersecting lines are those that cross each other) and intra– means “inside” (like intravenous).

Chemical signals are released by signaling cells in the form of small, usually volatile or soluble molecules called ligands. A ligand is a molecule that binds another specific molecule, in some cases, delivering a signal in the process. Ligands can thus be thought of as signaling molecules. Ligands interact with proteins in target cells, which are cells that are affected by chemical signals; these proteins are also called receptors. Ligands and receptors exist in several varieties; however, a specific ligand will have a specific receptor that typically binds only that ligand.

What You’ll Learn to Do

• Differentiate between different types of signals used by multicellular organisms
• Identify different types of signaling molecules
• Identify types of receptors, their molecular composition, and the differences among them

Learning Activities

The learning activities for this section include the following:

• Types of Signals
• Signaling Molecules
• Signaling Receptors
• Self Check: Signaling Molecules and Cellular Receptors