MCAT Diagnostic Passage 2

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NS_Tutor_Will
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Joined: Fri May 25, 2018 9:15 am

MCAT Diagnostic Passage 2

Post by NS_Tutor_Will » Thu Oct 25, 2018 1:45 pm

A student recently wrote in with questions about #6 and #8.
I believe this question is incorrect for 2 reasons: 1. Ploidy does not increase after cell replication. Ploidy does not refer to the total copies of chromosomes. It refers to the total copies of DISTINCT chromosome. Becuase the cell is simply replicating the chromosomes they have it is not distinct. Thus it remains 2n. 2. just becasue the cyst i increasing in the number of cells, doesn't mean ploidy for that organism increases. Ploidy would still refer to the number of distinct copies for each chromosome. By the logic used in this question, humans (having millions of cells and millions of replicated copies of DNA) would millionploidy!
According to this passage, there is not technically any cell replication going on. Instead, the parasites are replicating multiple nuclei without dividing. Note that these multiple nuclei are within the same cell and not within reproducing cells. In other words, we are looking at a single cell and there are many sets of chromosomes (16N, in fact, by virtue of the 4 tetraploid nuclei in the same cell). Remember, ploidy refers to the number of sets of chromosomes (and not to number of chromosomes). Humans are diploid (2N) because they have two sets of 23 chromosomes.
This question could have 2 answers including C. β-(1-3)-N-acetyl-D-galactosamine as it is clearly also integrated with the cwd proteins
Note that the cysts are actually formed by the organism itself, so only the cwp1-3 proteins are actually parasite proteins that leave the parasite. β-(1-3)-N-acetyl-D-galactosamine is a component of the cyst wall itself and is not synthesized by the parasite. In other words, the cwp1-3 are synthesized by and then leave the parasite to complex with the β-(1-3)-N-acetyl-D-galactosamine in the cyst wall.

I hope this helps clear up any confusion and good luck!
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