AAMC FL 2 BB Q42

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mgarc805
Posts: 35
Joined: Tue Jun 25, 2019 11:23 am

AAMC FL 2 BB Q42

Post by mgarc805 » Sun Jul 28, 2019 12:22 pm

the question is asking for the effect of mammalian proteases in the virus. my first train of thought is that these enzymes are only expressed in the mammalian cell so ther wouldn't be any effect on the virus but they are asking abut specifically the glycoproteins the virus uses to infect the cell. Which makes me wonder but then I read this sentence
The infectivity of VSV-EGP, vesicular stomatitis virus (VSV) particles engineered to contain EGP instead of VSV glycoprotein in the viral envelope, was reduced more than 99-fold by inhibitors of the mammalian proteases CatB and CatL
. basically inhibiting the mammalian proteases decreases the infectivity of the virus. I would think that is mammalian proteases had a effect on viral proteins then expression of the proteases is what would decrease the infectivity due to the degradation of the proteins used to infect. Again suggesting that there is no effect or at least that there is no protease activity. what is wrong with my train of thought?
NS_Tutor_Mathias
Posts: 264
Joined: Sat Mar 30, 2019 8:39 pm

Re: AAMC FL 2 BB Q42

Post by NS_Tutor_Mathias » Mon Jul 29, 2019 1:24 pm

my first train of thought is that these enzymes are only expressed in the mammalian cell so ther wouldn't be any effect on the virus
If first intuitions were any good, we would skip doing research entirely ;)

Before going any deeper, remember that a good fraction of MCAT passages (particularly B&B) try to present you with novel information - they describe to you a set of unexpected interactions, and want you to incorporate them and reason from these new assumptions, not your old ones.

The passage says that acid-dependent proteases cause conformational changes in EGP. This translates in regular english to "as I chop off bits of EGP while trying to digest it, it drastically changes shape". According to the passage, CatB and CatL are proteases - and you can infer that they are acid-dependent proteases (most of 'em are, because having pH 7 active proteases would be incredibly bad for cellular integrity). So CatB and CatL only ever really do one thing: Chop stuff up in the endosome/lysosome. That's also what they do to EGP.
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