BE230_Lecture_19&20

BE230_Lecture_19&20 - Cell Structure Function BE230...

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Cell Structure & Function BE230 Dr Christine Loscher Lecture 8/9
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Some G Proteins Activate the Inositol Phospholipid Signaling Pathway by Activating Phospholipase C- β Many G-protein-linked receptors exert their effects mainly via G proteins that activate the plasma-membrane-bound enzyme phospholipase C- β . The phospholipase acts on an inositol phospholipid (a phosphoinositide ) called phosphatidylinositol 4 , 5- bisphosphate [PI(4 , 5)P 2 ] , which is present in small amounts in the inner half of the plasma membrane lipid bilayer. Receptors that operate through this inositol phospholipid signaling pathway mainly activate a G protein called G q , which in turn activates phospholipase C- β , in much the same way that G s activates adenylyl cyclase.
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Some G Proteins Activate the Inositol Phospholipid Signaling Pathway by Activating Phospholipase C- β Three types of inositol phospholipids (phosphoinositides). The polyphosphoinositides PI(4)P and PI(4,5)P 2 are produced by the phosphorylation of phosphatidylinositol (PI) and PI(4)P, respectively. Although all three inositol phospholipids may be broken down in a signaling response, it is the breakdown of PI(4,5)P 2 that is most critical because it generates two intracellular mediators. Nevertheless, PI(4,5)P 2 is the least abundant, constituting less than 10% of the total inositol lipids and less than 1% of the total phospholipids in a cell.
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Activated phospholipase generates two products The activated phospholipase cleaves PI(4,5)P 2 to generate two products: inositol 1,4,5- trisphosphate (IP 3 ) and diacylglycerol . At this step, the signaling pathway splits into two branches. two branches of the pathway often collaborate in producing a full cellular response
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Inositol 1,4,5-trisphosphate (IP 3 ) small, water-soluble molecule that leaves the plasma membrane and diffuses rapidly through the cytosol When it reaches the endoplasmic reticulum (ER), it binds to and opens IP 3 -gated Ca 2+ -release channels in the ER membrane. Ca
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This note was uploaded on 01/05/2010 for the course FSH BT taught by Professor Ianmarison during the Fall '09 term at Dublin City University.

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BE230_Lecture_19&20 - Cell Structure Function BE230...

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