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 Names: Cell Biology; Zool 3200 Problem Set 1 1/28/16 Giardia are infectious unicellular organisms. When environmental conditions are harsh, Giardia form cysts, each of which contains two organisms, that help them withstand these environmental pressures. Giardia, shown below, have only a single type of subcellular organelle; they contain two nuclei. Given this, predict where on the evolutionary time scale these organisms likely arose. Explain your answer, which should not be an exact time but rather in terms of before/after which evolutionary events. (3 points) Mitochondria are thought to have been engulfed by an ancestral eukaryote sometime after oxygen began accumulating on this planet. Because Giardia are eukaryotic (they contain nuclei) but do not contain mitochondria, their evolutionary origin is likely sometime after nuclear enclosure of genetic material resulted in the diversion from eukaryotes and prokaryotes, but before too much oxygen in the atmosphere necessitated the engulfment of aerobic bacteria (that presumably gave rise to mitochondria). Your friend, a molecular biologist, wrote a grant proposal to the National Institutes of Health (NIH) to obtain some funding for his latest research idea. He proposed investigating mechanisms by which tumors develop using bacteria as a model organism. Do you believe his proposal deserves funding? Explain why his proposal may have been reasonable and/or why it or may not have been a good idea. (4 points) This proposal possibly deserves funding, but more information might allow for a better decision. Because tumors develop in multicellular organisms as a result of rapid cell growth, bacteria may be appropriate model organisms to study tumor development because bacteria use cellular components and processes that are very similar to those used by eukaryotic cancer cells. However, tumors only develop in eukaryotic multicellular organisms, and the interplay between multiple body systems influences that development. Thus, bacteria (which are unicellular prokaryotes) may not be appropriate model organisms to study tumor development. The antibiotic streptomycin inhibits the process of protein synthesis in bacteria. If this antibiotic is added to a culture of eukaryotic animal cells, protein synthesis in the cytoplasm and at the endoplasmic reticulum continues normally. Over time, however, the population of mitochondria in the cell becomes depleted. Specifically, it is observed that the protein‐synthesis machinery inside the mitochondria is inhibited. Explain this observation. (2 points) Mitochondria in eukaryotic cells are thought to have arisen as the result of an ancient eukaryote engulfing an aerobic prokaryote millions of years ago. Evidence supporting this hypothesis includes the circular DNA and the smaller ribosomes that are common to both prokaryotes and mitochondria. Because streptomycin is known to inhibit the process of prokaryotic protein synthesis (which requires ribosomes) and as well as protein synthesis by mitochondria (which also requires ribosomes), the common effect that the drug causes is likely a result of the similarities shared among the ribosomes of eukaryotic mitochondria and prokaryotes, which stems from their common evolutionary origin. The Go of the reaction: ATP ADP + Pi = ‐7.3 kcal/mol. If this reaction is taking place in a ‘closed system’ such that 1 mole of ATP is the only reagent initially added and no ADP or Pi product will be allowed to escape, how (if at all) will G of this reaction change over time? What factor(s) might influence G in this scenario? (2 points) Delta G of this reaction in a “closed system” will become more positive over time such that the reaction will become less favorable. This is because no additional reactants will be added so the amount of reactant available will become depleted as the reaction continues. Similarly, products will accumulate, driving the reaction back to the left. Thus, as time goes on the G will approach 0, which will be reached when the reaction reaches equilibrium. Circle the molecule in each of the following pairs that is more oxidized than the other. (3 points) CH3OH / CH2O NADPH / NAD+ CH3CHO / CH3CH2OH