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topic 9 f22 - Emily Lin Topic 9 Freeman Ch 22 This chapter...

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Emily Lin 4/13/11 Topic 9: Freeman Ch 22 This chapter introduces us to animal development, which starts out with gametogenesis. In sperm, the head contains the nucleus and an enzyme-filled structure called the acrosome. The neck encloses a centriole that is inherited by the fertilized egg. The mid-piece is packed with mitochondria that help it swim long distances. The tail region consists of a flagellum, composed of microtubules and surrounded by the plasma membrane. Eggs are large and immobile mainly because they contain nutrients required for the embryo’s early development and also cytoplasmic determinants that control the early events of development. In the egg, nutrients are provided by the yolk and they have cortical granules, which are small vesicles filled with enzymes activated during fertilization. Glycoproteins called the vitelline envelope forms around the egg, called the zona pellucida. Fertilization is when a sperm and egg fuse to make a diploid cell, or a zygote. The acrosomal reaction is triggered by contact between the sperm head and the jelly layer for the sperm to digest its way through the egg’s jelly layer by first releasing the enzymes, polymerization of actin into microfilaments that form the acrosomal process and the fusion of the plasma membrane. In sea urchins, fertilizin is a “lock” protein on the surface of eggs that binds to the bindin in a species-specific manner. Polyspermy through is avoided through a Ca2+
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