IMAT 2013 Q44 [Mitosis Phases]

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A liver cell in the metaphase of mitosis can be identified as being eukaryotic because it has:

  1. mitochondria
  2. ribosomes
  3. a nucleus

A. 1 only
B. 2 and 3 only
C. 1 and 3 only
D. 1 and 2 only
E. 1, 2 and 3

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The answer to this question is choice A.

What is this question asking for? Basically, it is asking you to discern which among of the choices is a correct association with eukaryotic features rather than prokaryotic ones.

To answer this question, let’s rationalize the wrong choices first, which are the ones that involved ribosomes and nuclei:

  • Ribosomes: Since you are trying to look for structures that are going to signify that the cell is indeed eukaryotic, this then is not a correct choice, As you know, both prokaryotes and eukaryotes are able to make proteins. With that being said, it would make sense that they would also have the molecular machinery to even make proteins in the first place, thus the need for ribosomes to perform the task of translation. To be specific, eukaryotes have ribosomes made up of the 60S and 40S subunits, while prokaryotes have ribosomes made up of the 50S and 30S subunits. Even though the subunits differ among prokaryotes and eukaryotes, the fact that BOTH of them have ribosomes makes this an incorrect answer.

  • Nucleus: You might be thinking, “But this is an organelle! Prokaryotes don’t have organelles, so why is this an incorrect answer?” Yes, prokaryotes don’t have a nucleus, but there is a very important detail in the question that eliminates this from your consideration. If you read back the question, it specifieed “A liver cell in the metaphase of mitosis”. This statement is a bit tricky if you do not pay close attention to it. If you are familiar with the phases of mitosis, you would know that the nuclear envelope starts to dissolve late prophase, in preparation to bring chromosomes at the metaphase plate for metaphase. So if you analyze it, would you see a nucleus at this phase? No, which means that you cannot identify this cell as being eukaryotic just yet, because of the absence of the nucleus at this point in the cell cycle.

This then leaves mitochondria, or choice A, as the only consideration left.

  • This answer logically follows, since the mitochondria is an organelle. And as you already know, the main distinguishing factor between eukaryotes and prokaryotes is the lack of compartmentalization in the latter, meaning that prokaryotes lack the different organelles that have specialized functions that eukaryotes have. In addition, the main reason this was the only answer, where nucleus was excluded, is because during the phase of mitosis, the mitochondria does not dissolve, thus stays intact during the cell cycle. Therefore, this makes it the correct answer.
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