| Calcium In Biology |
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Information AboutCalcium In Biology |
| CATEGORIES ABOUT CALCIUM IN BIOLOGY | |
| signal transduction | |
| calcium | |
| biology and pharmacology of chemical elements | |
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MEASURING CA<SUP>2+</SUP> IN LIVING TISSUE The total amount of Ca2+ present in a tissue may be measured using Atomic Absorption Spectrometry , in which the tissue is vapourized and combusted. To measure Ca2+ In Vivo , a range of Fluorescent Dyes may be used. These dyes are based on Ca2+-binding molecules such as BAPTA and so care is required in their use, because they may actually Buffer the Ca2+ changes which they are used to measure. ORGANS AND TISSUES Different Tissues contain Ca in different concentrations. In Vertebrate s Ca (mostly Calcium Phosphate and some Calcium Sulfate ) is the most important (and specific) element of Bone and calcified Cartilage . Some Invertebrate s use calcium compounds for building their Exoskeleton ( Shells and Carapace s) or Endoskeleton ( Echinoderm plates and Porifera n calcareous Spicule s). Many Protist s also make use of calcium. There are also some Plant s that accumulate Ca in their tissues, thus making them more firm. Calcium is stored as Ca- Oxalate crystals in Plastid s. CELL BIOLOGY In Eukaryotes , Ca2+ ions are one of the most widespread Second Messenger s used in signal transduction. They make their entrance into the Cytoplasm either from outside the cell through the Cell Membrane via calcium channels (such as Ca-binding Protein s), or from some internal Calcium Storage s. Ca2+ entering the cell plasma causes the ''specific action'' of the cell, whatever this action is: Secretory Cell s release Vesicle s with their Secretion , Muscle Cell s contract, Synapse s release Synaptic Vesicle s and go into processes of Synaptic Plasticity , etc. Calcium's function in Muscle Contraction was found as early as 1882 by Ringer and led the way for further investigations to reveal its role as a messenger about a century later. Because its action is interconnected with CAMP , they are called synarchic messengers. Calcium can bind to several different calcium-modulated proteins such as Troponin-C (the first one to be identified) or Calmodulin . The ions are stored in the Sarcoplasmic Reticulum of muscle cells. The same Ca2+ ions can, however, bring damage to cells if there are too many of them (for example in the case of Excitotoxicity , or Overexcitation of Neural Circuit s, which can occur after Brain Trauma or Stroke ). Excesses of calcium within a cell may damage it or even cause it to undergo Apoptosis . One cause of Hypercalcemia is Hyperparathyroidism . CALCIUM IN PLANTS Structural roles Ca2+ ions are an essential component of plant Cell Walls and Cell Membranes , and are used as Cations to balance Organic Anions in the plant Vacuole . The Ca2+ concentration of the vacuole may reach millimolar levels. The most striking use of Ca2+ ions as a structural element in plants occurs in the marine Coccolithophores , which use Ca2+ to form the Calcium Carbonate plates with which they are covered. Cell signalling Ca2+ ions are usually kept at nanomolar levels in the Cytosol of Plant Cells , and act in a number of signal transduction pathways. FOOD SOURCES The USDA web site has a very complete table of calcium content (in mg) of common foods per common measures (link below). Calcium amount in foods, 100 G :
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