Chapter 47 - Chapter 47 Animal Development The Acrosomal...

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Chapter 47: Animal Development The Acrosomal Reaction: This reaction begins when a specialized vesicle at the tip of the sperm (acrosome) discharges hydrolytic enzymes— vitelline layer: when molecules of a protein on the tip of the acrosomal process adheres to specific sperm receptor proteins that extend from the egg plasma membrane through the surrounding meshwork of extracellular matrix- lock and key recognition of molecules ensures that eggs will be fertilized only by sperm of the same species Contact of the tip of the acrosomal process with the egg membrane leads to the fusion of egg and sperm plasma membranes The sperm nucleus then enters the egg cytoplasm Contact and fusion of the membranes causes ion channels to open in the egg and change the membrane potential Change in membrane potential (depolarization) is a common feature of fertilization in mammals Occurring within 1-3 seconds after a sperm binds to an egg, depolarization prevents additional sperm from fusing with the egg’s plasma membrane Without this fast block to polyspermy, multiple sperm could fertilize an egg The Cortical Reaction: Within seconds after a sperm binds to an egg, cortical granules fuse with the egg plasma membrane, initiating the cortical reaction—secreted enzymes
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Chapter 47 - Chapter 47 Animal Development The Acrosomal...

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