Cells are constantly exposed to molecular signals that can come from the external environment or from within the body of a multicellular organism. To respond to a signal, the cell must have a specific receptor that detects the signal and activates some type of cellular response. Signal transduction pathways involve regulation of enzymes and transcription factors, and crosstalk often occurs between pathways.
learning outcomes
You should be able to:
Use the source and distribution mechanism of a signal to identify the type.
Give an example of how a particular type of signal (autocrine, juxtacrine, paracrine, or hormone) functions in an organism.
Explain how specificity is achieved in a signal transduction pathway.
Compare cells found in the same organism that can and cannot respond to a specific chemical signal.
Under what conditions would autocrine signaling be most advantageous for a cell?
Autocrine signaling would be important for a cell to maintain a specialized role. For example, a cell might receive a signal to specialize and form a tissue of many cells. The first cell would self-
How are hormones delivered to target cell receptors?
Hormones are delivered to target-
All cells have the potential to respond to all signals in an organism. What makes signaling specific?
Specificity for signal response occurs because only certain cells make the receptor for a given signal.
The general features of signal transduction pathways described in this section will recur in more detail throughout the chapter. First, let’s consider more closely the nature of the receptors that bind signal molecules.