6-20-08 - 6/20/08 Review: More calcium = destabilized CF,...

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6/20/08 Review: More calcium = destabilized CF, destroyed MPF = completion of 2 nd meiotic division = 2 unequal haploid cells: (1) a second polar body (dies) and (2) the female pronucleus (woo hoo!) The fusion of the sperm with the oolemma causes an increase in calcium and propels the secondary oocyte to complete the second meiotic division and become a female pronucleus. But how? Well, there are two explanations: (1) the receptor hypothesis and (2) the cytoplasmic factor hypothesis. In the receptor hypothesis, sperm binds with specific oolemma surface proteins which activates the G-protein . The G-protein causes dissociation of Gq-alpha. Gq-alpha activates a membrane-bound enzyme called Phospholipase C (PLC) (Inositol bisphosphate is a target for PLC). The PLC will then yield two more products: (1) Inositol triphosphate (IP 3 ) and (2) Diacylglycerol (DAG). Inositol triphosphate binds to IP 3 receptors on the endoplasmic reticulum to stimulate calcium release into the ooplasm. The diacylglycerol activates Protein Kinase C (PKC), which can also stimulate calcium release when interacting with the endoplasmic reticulum. The second hypothesis is called the cytoplasmic factor hypothesis. It states that, upon fusion of the sperm with the oolemma, the sperm releases a cytoplasmic factor called PLC zeta directly into the ooplasm. PLC
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6-20-08 - 6/20/08 Review: More calcium = destabilized CF,...

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