James P Hughes PhD


■ To introduce receptor structure, specificity, and regulation

■ To describe how ligand-receptor interaction initiates signaling

■ To present representative signaling pathways used by cells


4.1 Cellular Signaling 86

4.2 Receptor Binding 87

4.3 Signal Transduction via Nuclear Receptors 90

4.4 Signal Transduction via Membrane Receptors 93

4.5 Signaling in Apoptosis 101

Transducers convert energy from one form to another and signal transduction is the method by which signals are converted. The cell's molecular circuits sense, amplify, and integrate certain input signals received from its environment to generate responses such as changes in enzyme activity, gene expression, or ion-channel activity. Defects in these pathways are associated with cell dysfunction and disease. Cellular engineering aims at elucidating specific disease-related signal transduction cascades to generate novel drug targets and markers allowing for diagnosis of disease and tracking of disease progression.

Maintenance of homeostasis requires constant communication among cells. Messages must be sent in a timely manner, and they must be specific. Sometimes, specificity is maintained by cellular architecture. This is, for instance, the case when one neuron synapses on the next (see Chap. 6). But more often than not, specificity is determined by cellular receptors that recognize individual messages and translate (transduce) them into language that is meaningful to the cell. The structure of cellular receptors is introduced in Chap. 6 with emphasis on neuronal receptors. Receptor-associated recognition and translation are the complex processes that will be addressed in this chapter.

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