AAMC Stance on Methionine and Tyrosine

[DaAlienist]

Reading up on amino acids, and I have a few sources that say these two AA Tyr and Met are hydrophobic, while other references list them as polar.

I can see how they might be both, but how does the AAMC treat them? I have not gotten into any of the newer AAMC material yet and want to know which property the test considers correct.

http://bioch3mworld.files.wordpress.com/2013/03/aminoacids.jpg

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[Altius Premier Tutor]

I've always considered both methionine and tyrosine hydrophobic, while keeping in the back of my mind the fact that tyrosine has that -OH group, so if I am asked to compare its hydrophobicity to say phenylalanine I know for sure it is MORE polar. Methionine is a safe bet as nonpolar. Tyrosine is the one I've seen listed both ways. The AAMC authors are usually quite fair, so they probably wouldn't make a question hinge on that dilemma. However, that doesn't mean tyrosine might not be the best answer, or even the correct answer to a question about hydrophobic amino acids. For example, they might suggest that a portion of an enzyme is hydrophobic and ask which amino acid is likely to be found there, and tyrosine might be the most non-polar of the four available options.

 

[aldol16]

They most likely aren't going to ask a question that could be contentious since methionine and tyrosine, while they have sticky hydrocarbon components, could be interpreted as also containing polar components. Polar and hydrophobic are not necessarily mutually exclusive, if you get down to the details. Generally, you can interpret methionine as hydrophobic and tyrosine as slightly polar and hydrophilic. Here's a classical paper that actually measured the partitioning: http://www.biosyn.com/Images/ArticleImages/pdf/A simple.pdf

 

[DaAlienist]

They most likely aren't going to ask a question that could be contentious since methionine and tyrosine, while they have sticky hydrocarbon components, could be interpreted as also containing polar components. Polar and hydrophobic are not necessarily mutually exclusive, if you get down to the details. Generally, you can interpret methionine as hydrophobic and tyrosine as slightly polar and hydrophilic. Here's a classical paper that actually measured the partitioning: http://www.biosyn.com/Images/ArticleImages/pdf/A simple.pdf

@aldol16 @Altius Premier Tutor
Wow, that paper is almost 20 years older than me! Thanks for the tips y'all