A ligand - receiving cell Some gated ion channels respond...

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ligand-gated ion channel  is a type of membrane receptor that can act as a gate when  the receptor changes shape. When a signal molecule binds as a ligand to the receptor protein, the gate opens to allow the  flow of specific ions, such as Na +  or Ca 2+ , through a channel in the receptor. Binding by a ligand to the extracellular side changes the protein’s shape and opens the  channel. When the ligand dissociates from the receptor protein, the channel closes. The change in ion concentration within the cell may directly affect the activity of the cell. Ligand-gated ion channels are very important in the nervous system. For example, neurotransmitter molecules released at a synapse between two neurons bind as  ligands to ion channels on the receiving cell, causing the channels to open. Ions flow in and trigger an electrical signal that propagates down the length of the 
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Unformatted text preview: receiving cell. Some gated ion channels respond to electrical signals, instead of ligands. Concept 11.3 Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell The transduction stage of signaling is usually a multistep pathway. These pathways often greatly amplify the signal. If some molecules in a pathway transmit a signal to multiple molecules of the next component in the series, the result can be large numbers of activated molecules at the end of the pathway. A small number of signal molecules can produce a large cellular response. Also, multistep pathways provide more opportunities for coordination and regulation than do simpler systems....
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