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Midterm Exam Review

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University of Waterloo
BIOL 303
Dragana Miskovic

The wild imaginings of midterm content Fill your soul12Is the sperm activation the same as capacitation sea urchin and mammalacrosomal reaction must occur Acrosomal Reaction is sperm activation Capacitation is the maturation of the sperm Only Mature Sperm can fertilize the egg Fertilization implies the acrosomal reacitonWhy is it important to prevent polyspermy How is this done in the sea urchin What would happen to the sea urchin egg if it became polyspermic It is important to prevent polyspermy in order to allow successful reproduction to occur Aneuploidy on the level of chromosome sets would not cause viable offspring or successful divisions Polyspermy in a sea urchin eg two sperm fertilization would result in an incorrect number of sets of chromosomes triploid in the nucleus Division would then be inconsistent in terms of genetic content sets of chromosomes aneuploidy would occur as a result of nondisjunction and would cause improper development if it develops at all Describe and distinguish between the fast block to polyspermy and the slow block to polyspermy The fast block and slow block are adaptive reactions to fertilization that occur within secondsminutes of fertilization to prevent polyspermy The Fast Block involves a change in electrical potential through hyperpolarizing and depolarizing means on the cellular membrane of the egg and occurs within 13 seconds postfertilization and is transient lasts 1minute The resting potential shifts from 70 low Nainside cell vs high Na in the sea water to 20mv by influx of Na ions Cl ions can be used in some amphibians due to different environmental conditions Because this is a transient change the fast block functions as a delaying of polyspermy that allows the slow block to work for more permanent changeThe Slow Block to polyspermy involves the cortical granule reaction and happens1 minutes post fertilization This is accomplished by fusion of the cortical granules with the egg cell membranereleases contents into the space between the cell membrane and the vitelline envelope that modify the extracellular space Proteins include Serine Protease digests bindin receptorssperm is clipped off digests protein holding the egg cell membrane to the vitelline envelope Creates the fertilization envelope by fusion of components of the granule and the vitelline envelope Mucopolysaccharidescreate an osmotic gradient causing water to enter and expand the envelope and Peroxidase enzymesharden the envelope by crosslinking tyrosine residues Finally a hyalin coating is formed around the egg
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