Biology Study Guide Final Exam Chapter 47

Biology Study Guide Final Exam Chapter 47 - Study Guide:...

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Study Guide: Final Exam Chapter 47: Animal Development 1. Two functions of fertilization (union of haploid gametes to produce a diploid zygote) are to combine haploid sets of chromosomes from two individuals into a single diploid cell, the zygote and the activation of the egg. Contact of the sperm with the egg’s surface initiates metabolic reactions within the egg that trigger the onset of embryonic development. 2. The acrosomal reaction is when the head of the sperm comes into contact with the jelly coat of the egg. acrosome, a specialized vesicle at the tip of the sperm, discharges its contents by exocytosis, which is enabled by hydrolytic enzymes. The tip of the acrosomal process adheres to special receptor proteins on the egg’s surface. These receptors extend through the vitelline layer, just external to the egg’s plasma membrane. The sperm and egg plasma membranes fuse, and the sperm nucleus enters the egg’s cytoplasm. Na + channels in the egg’s plasma membrane open and Na + ions flow into the egg, and the membrane depolarizes, changing the membrane potential of the egg. Depolarization prevents additional sperm from fusing with the egg’s plasma membrane. This fast block to polyspermy prevents polyspermy, the fertilization of the egg by multiple sperm. 3. Cortical reaction , the fusion with the egg’s plasma membrane of numerous vesicles lying in the egg’s cortex, the area just beneath the membrane. Ca 2 + from the egg’s endoplasmic reticulum is released into the cytosol. High concentrations of Ca 2 + cause cortical granules to fuse with the plasma membrane and release their contents into the perivitelline space, the space between the plasma membrane and the vitelline layer. The vitelline layer hardens into a fertilization envelope, which resists the entry of additional sperm. The fertilization envelope and other changes in the egg’s surface function together as a long-term slow block to polyspermy. The plasma membrane returns to normal, and the fast block to polyspermy no longer functions. 4. Acrosomal and cortical reactions function sequentially to prevent polyspermy because the acrosomal reaction is triggered when the sperm meets the eggs. Hense, releasing hydrolytic enzymes that digest material surrounding the egg. A hole is made in the vitelline layer, allowing contact and fusion of the the gamete plasma membrane becomes depolarized, resulting in fast block polyspermy. Once the sperm enters the egg cytoplasm, fusion of gamete membranes triggers the release of Ca 2 + from the ER into the egg’s cytosol, causing cortical granules in the egg to fuse with the plasma membrane and discharge their contents, which leads to the swelling of the previtelline space, hardening of the vitelline layer, and clipping of sperm binding receptors. The resulting fertilization is the slow block to polyspermy.
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This note was uploaded on 11/04/2010 for the course BIO 107 taught by Professor Abott during the Fall '09 term at UConn.

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Biology Study Guide Final Exam Chapter 47 - Study Guide:...

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