Signal Transduction: From Extracellular Signal to Cellular Response
Many cells sense and respond to light or physical stimuli such as touch or heat.
All cells communicate through extracellular signals. In unicellular organisms, extracellular signaling molecules regulate interactions between individuals, while in multicellular organisms, they mainly regulate physiology and development.
External signals include membrane-
Hydrophobic signaling molecules interact with cytosolic receptors and mainly affect gene expression.
Binding of a hydrophilic extracellular signaling molecule to a cell-
Signals from one cell act on distant cells in endocrine signaling, on nearby cells in paracrine signaling, or on the signaling cell itself in autocrine signaling (see Figure 15-2).
Protein phosphorylation and de-
GTP-
Some nonprotein, low-
Signal transduction pathways allow amplification of an extracellular signal, enabling activation of a relatively small number of cell-