Chapter 11 - C hapter Eleven: Cell Communication...

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Chapter Eleven: Cell Communication Definitions 1) Signal transduction pathway: is the process by which a signal on a cell’s surface in converted to a specific cellular response in a series of steps. 2) Quorum sensing: is a phenomenon in which the concentration of signaling molecules allows bacteria to sense the local density of bacterial cells. 3) Biofilms: are aggregations of bacteria that often form recognizable structures containing regions of specialized functions. Notes - Paracrine signaling is a type of local signaling. - Both animals and plants use chemicals called hormones for long-distance signaling. - Stages of cell signaling: Reception: o It is the target cell’s detection of a signaling molecule coming from outside the cell. A chemical signal is detected when the signaling molecule binds to a receptor protein located at the cell’s surface or inside the cell. o A ligand is a term for a molecule that specifically binds to another molecule, often a larger one. o Receptors in the plasma membrane: Their ligands are water-soluble and generally too large to pass freely through the plasma membrane. Types of membrane receptors: G protein-coupled receptors:
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o They are plasma membrane receptors that work with the help of a G protein, a protein that binds to the energy-rich molecule GTP. o They each have seven helices spanning the membrane. α o Pharmacologists now realize that up to 60 % of all medicines used today exert their effects by influencing G-protein pathways. o G protein pathway: Loosely attached to the cytoplasmic side of the membrane, the G protein functions as a molecular switch that is either on or off, depending on which two guanine nucleotides is attached, GDP (inactive) or GTP (active). When the appropriate signaling molecule binds to the extracellular side of the receptor, the receptor is activated and changes shape. Its cytoplasmic side then binds to an inactive G protein, causing a GTP to displace the GDP. This activates the G protein. The activated G protein dissociates from the receptor, diffuses along the membrane, and then binds to the enzyme, altering the enzymes shape and activity. When the enzyme is activated, it can trigger the next step in a pathway leading to a cellular response. G protein also functions as a GTPase; it then hydrolyzes its bound
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This note was uploaded on 09/09/2011 for the course BIO 101 taught by Professor Harounal-rashed during the Spring '11 term at King's College London.

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Chapter 11 - C hapter Eleven: Cell Communication...

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