CellCommPrint - Cellular Communication I think we've used...

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Cellular Communication I think we've used this joke before, but communication within and between cells is much more important to human life than high profile business phone calls.
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Ligands Bind to Receptors How to cells communicate? Cells communicate by sending and receiving signals. These extracellular signals begin as molecules (often referred to as ligands) that can be secreted from the signaling cell into the extracellular space where it acts on a target cell that has a receptor for the ligand. Ligands can also be attached to the surface of a signaling cell whereby the signal is propogated to the cells that are juxtaposed to the signaling cell via cell-cell contact. How does the binding of a ligand to a receptor result in a signaling event? This occurs via a conformational change in the receptor that results in the propagation of a signal in the target cell. Let's take a look at a classic example of this. In the absence of a ligand a cell surface receptor is in the off position meaning that this receptor is not able to propagate a signal (Figure 1A). When the ligand binds to its receptor the receptor undergoes a conformational change that turns “on” the receptor and initiates a signaling cascade in the target cell. These receptors can also be ion channels whereby the binding of a ligand to the channel either opens or closes the channel which can result in changes in the membrane potential of the target cell and the initiation of a signaling event. Cellular Communication
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Figure 2. Extracellular signals only bind to specific receptors and cells only express certain receptors. This insures that only the cell will respond to the extracellular signal. Figure3. Classifications of cell signaling events Signaling is Propagated by Extracellular and Intracellular Molecules Signaling molecules can be chemicals, proteins, lipids, nucleic acids and even dissolved gases such as nitric oxide. Most receptors are located on the surface of a cell (cell surface receptors) but some are located inside the cell ( intracellular receptors ). Signal molecules can only interact with their specific receptors. Think of a lock and key mechanism with the receptor being the lock and the signal being the key. This is important because cells are exposed to hundreds of different signals in their environment and they have to be able to distinguish between them. In other words, if the cell does not express the specific receptor for a signal molecule, it will not respond to that signal molecule (Figure 2). Remember, although all normal cells will have the gene for every kind of receptor , it will only be expressed in some of them as proteins. Cell specialization that occurs during development will determine which receptor genes are expressed and which are not. Sometimes these signal molecules travel over long distances to their target
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This note was uploaded on 04/21/2008 for the course BIOL 100 taught by Professor Lee during the Winter '07 term at San Diego State.

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CellCommPrint - Cellular Communication I think we've used...

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