8: Signaling
- Page ID
- 2929
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Cells must receive and respond to signals from their surroundings. Cellular signals and the pathways through which they are passed on and amplified to produce the desired effects on their targets are the focus of this section.
- 8.1: Cell Signaling
- How do cells receive signals from their environment and how do they communicate among themselves? It is intuitively obvious that even bacterial cells must be able to sense features of their environment, such as the presence of nutrients or toxins, if they are to survive. In addition to being able to receive information from the environment, multicellular organisms must find ways by which their cells can communicate among themselves.
- 8.2: Ligand-gated Ion Channel Receptors
- The simplest and fastest of signal pathways is seen in the case of signals whose receptors are gated ion channels. Gated ion channels are made up of multiple transmembrane proteins that create a pore, or channel, in the cell membrane. Depending upon its type, each ion channel is specific to the passage of a particular ionic species.
- 8.3: Nuclear Hormone Receptors
- Another type of relatively simple, though much slower, signaling is seen in pathways in which the signals are steroid hormones, like estrogen or testosterone. Steroid hormones are related to cholesterol, and as hydrophobic molecules, they are able to cross the cell membrane by themselves.
- 8.4: G-protein Coupled Receptors (GPCRs)
- G-protein coupled receptors are involved in responses of cells to many different kinds of signals, from epinephrine, to odors, to light. In fact, a variety of physiological phenomena including vision, taste, smell and the fight-or-flight response are mediated by GPCRs.
- 8.5: Receptor Tyrosine Kinases (RTKs)
- Receptor tyrosine kinases mediate responses to a large number of signals, including peptide hormones like insulin and growth factors like epidermal growth factor. Like the GPCRs, receptor tyrosine kinases bind a signal, then pass the message on through a series of intracellular molecules, the last of which acts on target proteins to change the state of the cell.