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In animal cells - 2 is so low small changes in the absolute...

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In animal cells, increases in Ca 2+  concentrations may cause contraction of muscle cells,  secretion of certain substances, and cell division. o In plant cells, increases in Ca 2+  trigger responses such as the pathway for greening in response  to light. Cells use Ca 2+  as a second messenger in both G-protein pathways and tyrosine-kinase  pathways. The Ca 2+  concentration in the cytosol is typically much lower than the concentration outside the  cell, often by a factor of 10,000 or more. o Various proteins actively transport Ca 2+  outside the cell or into the endoplasmic reticulum  (ER) or other organelles. o As a result, the concentration of Ca 2+  in the ER is usually much higher than the concentration  in the cytosol. Because the concentration of cytosolic Ca
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Unformatted text preview: 2+ is so low, small changes in the absolute numbers of ions cause a relatively large percentage change in the Ca 2+ concentration. Signal transduction pathways trigger the release of Ca 2+ from the cell’s ER. The pathways leading to calcium release involve still other second messengers, diacylglycerol (DAG) and inositol trisphosphate (IP 3 ) . o DAG and IP 3 are created when a phospholipase cleaves a specific membrane phospholipid. o The phospholipase may be activated by a G protein or by a tyrosine-kinase receptor. o IP 3 activates a gated calcium channel, releasing Ca 2+ from the ER. o Calcium ions activate the next protein in a signal transduction pathway....
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