Chapter 11 - Chapter 11: Overview of Cell Signaling Cell...

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Chapter 11:   Cell Communication Overview of Cell Signaling A chemical signal from outside the cell ( a.k.a. “ligand”) binds with a protein receptor molecule (usually on the cell surface,  but may be located intracellularly) specifically designed to recognize the signal chemical.  The binding of the signal to the receptor  changes the 3-D shape of the receptor. This shape change activates an intracellular enzyme (located close to the plasma membrane  receptor) which initiates the transduction pathway. Transduction (conversion of the chemical signal into a cell response or responses) may involve one or more “relay molecules”  (i.e., G-proteins, cAMP, phosphokinases, phosphatases, etc.). Every chemical involved in a transduction pathway beyond the  membrane-bound receptor, up to and including the last enzyme in the pathway responsible for initiating an intracellular response is  considered a “relay molecule.”  Some relay molecules, such as membrane-bound proteins, serve as transducers.  Some relay molecules,  such as phosphokinases, serve as amplifiers.  Phosphokinases (a.k.a. protein kinases) amplify the original signal within the cytoplasm  by phosphorylating a variety of intermediate enzymes in a series of cascade reactions.  Multi-step pathways provide more  opportunities for coordination and regulation of a specific response.  Once each phosphokinase-catalyzed reaction is completed, the  activated enzyme is deactivated by a de-phosphorylating phosphatase enzyme. (Phosphatases may be considered “de-amplifiers”.) The last relay molecule in the transduction (or amplification) pathway activates an intracellular enzyme, or a gene, that  triggers a specific cell response or responses.  Cell responses include:   (a)  protein synthesis   (b)  enzyme activation (or deactivation) (c)  chemical synthesis and secretion (d)  cell division (mitosis or meiosis) (e)  plasma membrane permeability changes 1 of 12
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This note was uploaded on 04/07/2008 for the course BIO 101 taught by Professor Stein during the Spring '07 term at South Carolina.

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Chapter 11 - Chapter 11: Overview of Cell Signaling Cell...

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