Describe how a cell propagates a signal

Once a ligand binds to a receptor, the signal is transmitted through the membrane and into the cytoplasm. Continuation of a signal in this manner is called signal transduction. Signal transduction only occurs with cell-surface receptors because internal receptors are able to interact directly with DNA in the nucleus to initiate protein synthesis.

When a ligand binds to its receptor, conformational changes occur that affect the receptor’s intracellular domain. Conformational changes of the extracellular domain upon ligand binding can propagate through the membrane region of the receptor and lead to activation of the intracellular domain or its associated proteins. In some cases, binding of the ligand causes dimerization of the receptor, which means that two receptors bind to each other to form a stable complex called a dimer. A dimer is a chemical compound formed when two molecules (often identical) join together. The binding of the receptors in this manner enables their intracellular domains to come into close contact and activate each other.

What You’ll Learn to Do

• Explain how the binding of a ligand initiates signal transduction throughout a cell
• Recognize the role of phosphorylation in the transmission of intracellular signals
• Evaluate the role of second messengers in signal transmission

Learning Activities

The learning activities for this section include the following:

• Binding Initiates a Signaling Pathway
• Methods of Intracellular Signaling
• Self Check: Propagation of the Signal