AAMC Scored B/B #21

[laczlacylaci]

I thought the structure exhibited polarity, which would cause trouble in diffusing. I guess the rings created more hydrophobicity. Is the lactam considered polar, but it is overwhelmed by the rings? (like steriods can diffuse across membranes just fine)

In what case would we choose active transport and receptor mediated endocytosis?
What is considered a large molecule? I thought the size of the molecule would also trouble diffusion...

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[DrHart]

I put B first but ended up changing my answer to C. Would definitely like hear a solid explanation.

I guess my reasoning was that the polar areas of this molecule were so small relative to the nonpolar areas - so in terms of what AAMC would classify it as, I figured it would be nonpolar. If its four or five rings (similar to steroids), I usually assume it can pass through the membrane.
If there were more pronounced polar groups (like a couple carboxylic acids, etc.), I would've called it polar. Probably wouldn't consider it too large until maybe 10+ rings... ? Beats me

 

[TheLongGame]

The easiest way to determine if a molecule is polar (without access to electronegativity charts and actually calculating the moment) is to draw lines of symmetry and count free electrons. Any free electrons that your line of symmetry cuts through are zeroed out as "non factor". Then simply count the remaining free electrons on either side of your symmetry line. You will have to take into account the actual bond geometries and what is known about bond behaviors, conjugated systems, and formal charges, but the overall concept is pretty simple.


As to what constitutes a "large molecule" that is something I am wondering about myself!


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