Quick question

[PreparationIsKey]

Hey so I was wondering if the MCAT 2015 will be expecting us to know this question or a question such depth into viruses.

---Question starts here:

Some viruses can be crystallized and their structures analyzed. One such virus is Desmodium, or yellow mottle virus, which infects beans. This is a member of the tymovirus group and has a single-stranded RNA genome of ~6,300 nucleotides. Its virion is 25—30 nm in diameter, and is made up of 180 copies of a single capsid protein that self-associate to form each capsomere, which has icosahedral symmetry with 20 facets.

28) If this virus has capsomeres with 20 facets, how many proteins form each one?
A) 1
B) 5
C) ~6
D) ~20
E) ~180

---Mind you this is very extensive into the anatomy of the virus. I've read the 2015 MCAT PDF. Although it does state that we need to know viruses I wouldn't say to this extent. What do you guys say?




P.S. The answer is C.

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[lumpyduster]

I work with a very similar virus. I doubt you would need to know this, but in order to achieve icosahedral symmetry, you need pentamers. The hexamers form the 20 faces (facets) of the virus, whereas the 12 vertices are made of pentamers. 20 faces, made of 6 proteins each to form hexamers, give you 120 proteins. 12 corners with 5 proteins each (the pentamers) give you 60 proteins. 120+60 = 180.

It's funny because I just read "desdomonium" and skipped to the description of the virus and was like "how odd it's made of 180 identical proteins just like my virus... oh it has icosahedral symmetry too..." and then I saw it was a mottle virus and realized it's a cousin of my virus

 

[owlegrad]

We have a whole forum for questions like this. Check out the MCAT forum.