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Ch 4 Learning Objectives

Ch 4 Learning Objectives - Ch 4 Learning Objectives Monday...

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Ch 4 Learning Objectives Monday, October 11, 2010 4:47 PM List and describe the four major events that occur during fertilization. o Contact and recognition between sperm and egg. In most cases, this ensures that the sperm and egg are of the same species. o Regulation of sperm entry into the egg. Only one sperm nucleus can ultimately unite with the egg nucleus. This is usually accomplished by allowing only one sperm to enter the egg and actively inhibiting any others from entering. o Fusion of the genetic material of sperm and egg. o Activation of egg metabolism to start development. Describe the process of sperm differentiation. The centriole produces a long flagellum at what will become the posterior end of the sperm, and the Golgi apparatus forms the acrosomal vesicle at the future anterior end. The mitochondria collect around the flagellum near the base of the haploid nucleus and become incorporated into the midpiece ("neck") of the sperm. The remaining cytoplasm is jettisoned
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and the nucleus condenses. The size of the mature sperm in the figure has been enlarged relative to the other stages. Explain the importance of the structural features of the sperm cell: o Acrosome - the acrosome is derived from the Golgi and contains enzymes that digest proteins and complex sugars. It can be considered a modified secretory vesicle. The enzymes are used to digest a path through the outer coverings of the egg. In many species, a region of globular actin proteins lies between the nucleus and the acrosomal vesicle. These are used to extend a finger-like acrosomal process from the sperm during early stages of fertilization. The acrosome and nucleus together form the sperm head. o Flagellum (axoneme, sperm tail) - an individual sperm is able to travel by whipping its flagellum, the motor portion of which is known as the axoneme. The axoneme is formed by microtubules emanating from the centriole at the base of the sperm nucleus. The core of the axoneme consists of two central microtubules surrounded by 9 doublet microtubules (only one in the doublet is actually complete, having 13 protofilaments, while the other only has 11 and is C shaped). The interconnected protofilaments are made of the dimeric protein tubulin. The force of sperm propulsion is dynein, a protein attached to the microtubules. Dynein is an ATPase that uses ATP to allow the outer sliding of the outer doublet microtubules, causing the flagellum to bend. o Mitochondria - mitochondria are located in the midpiece of the sperm. In many species, a layer of dense fibers has interposed itself between the mitochondrial sheath and the cell membrane. This stiffens the sperm tail and prevents the head from being whipped around too violently. Explain the importance of each egg component: o Proteins are present in the egg so that the embryo is able to feed itself until it can obtain nutrients from the mother. These proteins are synthesized elsewhere (liver, fat bodies) and travel through the maternal bloodstream to the oocyte to form the yolk.
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