Biology, MCAT QBook question 261-268

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kleshchuk
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Joined: Tue May 12, 2020 10:27 pm

Biology, MCAT QBook question 261-268

Post by kleshchuk » Thu May 14, 2020 7:09 pm

For 261 A, they say that because we don't know whether the protein is of host or viral origin, there is no way of knowing if it will be recognized as foreign by the immune system. If it is a host protein, then it will not bind to the variable domain of an antibody. Why won't the protein bind to the variable domain of an antibody?

Also, for 261, I am confused how they came up with the answer for c?

For 267, how do you know that KSHV does not infect bacteria?

For 268, I have a couple questions. They say that it couldn't be -RNA virus because it would be nonfunctional. Are -RNA virus always nonfunctional? Also, do cytoplasmic exonucleases function breaking down DNA only when it is injected floating freely in the cytoplasm or is it in this case specifically the DNA is viral, meaning it is foreign?
NS_Tutor_Mathias
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Re: Biology, MCAT QBook question 261-268

Post by NS_Tutor_Mathias » Fri May 15, 2020 2:18 pm

261. If host antibodies bound host proteins, the host would suffer from autoimmunity. Depending on how and where this occurs, that makes for either a poor quality of life or is fatal. Since this is a virus, it could potentially express a host protein on its surface.

As for answer C: Because it is made by the host cell. The host is said to be human, so we know they have an ER and that this is the location of the majority of protein synthesis - in particular of membrane-bound protein synthesis. Therefore this protein must have been made in the ER.

267. Viruses rely on host cellular machinery to function and are as such virtually always highly specific to hosts - at least to the degree that a complete cross-over between domains of life for a virus is highly unlikely. So if it is given in the stem that KSHV causes cancer by infecting human cells, it is extremely unlikely that it would have any effect on bacteria.

268. Exonucleases breakdown any unprotected RNA or DNA - meaning linear forms without poly(A) tails and 5' GTP caps. This excludes mature transcripts which do exhibit these two features, as well as circular DNA such as plasmids.

-ssRNA genomes do not have poly(A) tails and therefore their genome, without viral capsid and possibly an envelope, is harmless.
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