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Bio B11 Lec 23 C15 Signal Transduction III.docx

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University of Toronto Scarborough
Biological Sciences
Dan Riggs

Bio B11 Lec 23 C15 Signal Transduction III Don't memorize these, just be aware of em. Fig 15-26: Ca2+ floods cytoplasm of cardian muscle cell. Response = triggers muscle contraction, and heart beats. Yellow thing = membrane bound pumps, use ATP. Calcium-Induced Calcium Release occurring in cardiac muscle cell. A depolarization in membrane voltage causes the opening of voltage-gated calcium channels in the plasma membrane, allowing entry of a small amount of Ca2+ into the cytosol (step1). The calcium ions bind to ryanodine receptors in the SER membrane (step 2), leading to release of stored Ca2+ in the cytosol (step3), which triggers the cell's contraction. The Ca2+ ions are then removed from the cytosol by the action of Ca2+ pumps located in the membrane of the SER (step4) and a Na+/Ca2+ secondary transport system in the plasms membrane (step 5), which leads to relaxation. This cycle is repeated after each heart beat. You have an egg and a sperm, the sperm fertilizes the egg, result is a diploid single cell organism, rapid series of divisions. Immediately after fertilization there is a large change in the levels of intercellular calcium. Flourescent dye is calcium specific, no Ca = No fluorescence. Lots of Ca = bright / strong fluorescent signal. T= 0 egg fertilized by sperm, red = high levels Ca spread through cell. *** Ca2+ activates cell division through CDK activation.*** Photo of epidermis of leaf, plants protect themselves from water loss by changing the shape of these uard cells, needs to balance h2o. Ca responds to changes in ABA, a stress hormone, regulates opening/closing of stomates by regulating shape of the guard cell. When open they're plump, and round because they havetaken in h2O. ABA signalling @ the plasms membrane. Binds to vacuole, causes Ca induced Ca release, when eflux channels open, lots of ions leave cell, followed by a loss of h2o. Thus water loss is regulated by changes in solute IE: ion. A simplified model of the role of Ca2+ in guard cell closure. (b): One of the factors controlling stomatal pore size is the hormone abscisic acid (ABA). WHen ABA levels rise, calcium ion channels in the plasms membrane are opened, allowing the influx of Ca2+ (step 1), which triggers the release of Ca2+ from internal stores (step 2). The subsequent elevation of intracellular
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