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Comments ...

 +1  (nbme23#7)

I was thinking signal sequence on the N-terminal end that would direct the protein into the RER to be then implanted into the plasma membrane. I guess transmembrane region is the better more specific answer?

drdoom  A bilayer has hydrophobic tails (polar head + nonpolar tails). If the N-terminus could be embedded in there, it would also have to be hydrophobic; but if an N-terminus were hydrophobic, it wouldn't dissolve well in the cytosol (=mostly water). In fact, an N-terminus probably wouldn't dissolve at all. If it were hydrophobic, it would aggregate with other, nearby N-terminuses (or other hydrophobic motifs). But if that happened, shuttle proteins couldn't recognize N-terminuses in the first place (they wouldn't be sterically accessible), nor deliver them to the rER.

Subcomments ...

submitted by hayayah(884),

Coloboma is an eye abnormality that occurs before birth. They're missing pieces of tissue in structures that form the eye.

  • Colobomas affecting the iris, which result in a "keyhole" appearance of the pupil, generally do not lead to vision loss.

  • Colobomas involving the retina result in vision loss in specific parts of the visual field.

  • Large retinal colobomas or those affecting the optic nerve can cause low vision, which means vision loss that cannot be completely corrected with glasses or contact lenses.

mousie  thanks for this explanation! +  
macrohphage95  can any one explain to me why not lens ? +  
krewfoo99  @macrophage95 Lens are an interal part of the refractive power of the eye. Without the lens the image would not be formed on the retina, thus leading to visual loss +2  
qfever  Do anyone know why not choroid? +  
adong  @qfever, no choroid would also be more detrimental to vision since it supplies blood to the retina +2  
irgunner  That random zanki card with colobomas associated with a failure of the choroid fissure to close messed me up +1  
mnemonicsfordayz  Seems like the key to this question is in what is omitted from the question stem: there is no mention of vision loss. If we assume there is no vision loss, then we can eliminate things associated with visual acuity (weird to think of in 2 week old but whatever): C, D, E, F. Also, by @hayayah 's reasoning, we eliminate E & F. If you reconsider the "asymmetric left pupil" then the only likely answer between A & B is B, Iris because the iris' central opening forms the pupil. I mistakenly put A because I was thinking of the choroid fissure and I read the question incorrectly - but it's a poorly worded question IMO. +  

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