AAMC #7; Passage VII

[brownhamster]

I had a lot of trouble with this passage. I was wondering if someone could help me understand the experiment, especially the experiment presented in figure two. Exactly when are they separating the cells and putting them back together?

#138. It seems like the two cells were treated with a drug that either inhibited transcription or translation. Since the cells communicated through proteins, the cells which had translation blocked didn't differentiate. That was the point of the question. But I can't figure out the logic. If you're blocking transcription, aren't you blocking translation also?

#141. How would you reason this through looking the passage? I'm reading the explanation given, but I still don't quite get it. Anyone understand the passage and logically come up with the right answer? What was your thought process?

#142. Same with this one, what was your thought process?

I know answering these questions require you to open up your tests, but I appreciate it.

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[PiBond]

The Passage: we're essentially separating different cells from the blastomere of a nematode and watching how it effects the fate of the cells (ie what tissue types the different cells yield). in the process, we discover that cells communicate with each other and that if we inhibit certain cellular processes then we get an absence of certain tissue types.

138: the best answer is protein. the key to this question is to simple focus on the information given in the passage--we start to second guess ourselves if we think outside the MCAT box. we see that if we inhibit transcription with actinomycin we get the tissue types: neurons, skin and muscle. if we inhibit translation with cycloheximide we only get neurons and skin. therefore, we get less tissue types by directly inhibiting translation (protein production).

141: first eliminate D since it's not a somatic/visceral cell type. next use figure 1 and notice that gut is the only tissue type that comes from only a single cell (that being EMS - E). neuronal and muscle come from several different cell types.

142: experiments 1 and 3 are what give us the correct answer here. eliminate A because it's entirely false. answer D is not mentioned or alluded to in any of the experiments. choice B mirrors what we did in the experiment to prove how cell differentiation depends on cell-to-cell communication, but it doesn't answer the question of how cells adopt fates different from their neighbors.