Signal-Transduction Pathways

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  • 13.1 Signal Transduction Depends on Molecular Circuits

  • 13.2 Receptor Proteins Transmit Information into the Cell

  • 13.3 Some Receptors Dimerize in Response to Ligand Binding and Recruit Tyrosine Kinases

  • 13.4 Metabolism in Context: Insulin Signaling Regulates Metabolism

  • 13.5 Calcium Ion Is a Ubiquitous Cytoplasmic Messenger

  • 13.6 Defects in Signaling Pathways Can Lead to Diseases

Signal transduction is an important capability in all life forms. It allows an organism to sense its environment and formulate the proper biochemical response. Just as the computer chip has “on–off” switches that allow the transmission of information, cells have molecular “on–off” switches that allow the transmission of information in the cell and between cells.

This chapter provides an overview of how cells receive, process, and respond to information from the environment, whether the information is in the form of light, smell, or blood-glucose concentration. Signal-transduction cascades mediate the sensing and processing of these stimuli. These molecular circuits detect, amplify, and integrate diverse external signals to generate responses such as changes in enzyme activity, gene expression, or ionchannel activity. This chapter introduces some of the basic principles of signal transduction and important classes of molecules that participate in common signal-transduction pathways.