Week Four

17 Pages

Biological Sciences
Course Code
BIOL 3156

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Week FourOctober 2226Defining Zygote PolarityThe first polar body formswhere this happens is the animal pole 180 opposite of this is the vegetal poleActivation of Protein SynthesisRecall the NaH antiport as one sodium comes in one hydrogen comes outthis causes a pH shift 68 to about 78Very shortly after fertilization there is a burst of protein synthesis This occurs before the first cleavage but continues for a very considerable amount of time14The red graph line represents the incorporation of C valine in protein There is a peak within about 5 hours after fertilization It levels off at 5 hours and decreases a little bit Then there is another burst at a much later time point This is a special point where this new burst is initiatedProtein synthesis appears to be strictly the result of proteins being translated No or little new RNA is being made It is relying on the stores of internal mRNA This mRNA is probably masked until this pointHow do we know that no new RNA is being producedActinomycin D treated with seawaterprotein synthesis still continues to come to a peak at about 5 hours After this time there is a rapid decrease in protein synthesis Actinomycin D blocks transcriptionthe peak at 5 hours shows that translation is using stored mRNA Other animal systems may be producing RNA earlier than in the sea urchins Cytoplasmic redistributionsamphibiansExamplecertain types of molecules are distributed at specific ends of the cytoplasm syncytialPrior to fertilization amphibians have a very heavily pigmented cytoplasm in the animal hemisphere and a clear cytoplasm in the vegetal hemisphere Sperm entry occurs relatively 30 above the equator in the animal hemisphere for these species The sperm sets of a sperm aster made of microtubules These microtubules interact with the cortical cytoplasm and shift it around the egg slightly so that a window opens up that reveals a grey cytoplasm grey crescent This section above the equator but part of the grey crescent will also be the site of the future dorsal lip of the blastopore Cytoplasmic rearrangement in the Tunicate eggPrior to fertilization there is a chorion The oocyte nucleus is actual a germinal vesicle The sperm enters in the vegetal pole in this instance The yellow cytoplasm is going to reconfigure itself as well The polar body is going to be extruded from the material from the oocyte nucleus area animal pole Styela
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