Classification of Amino Acids (Hydrophobic/Hydrophilic Polar/NonPolar)

[PreMade]

There seems to be contradicting information when it comes to classifying amino acids. Textbooks and websites have different classifications.

Anybody know which is correct and which is not? How do I know which is official?

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[Labrat07]

Can you give us some examples??? Not sure what you're asking.

Usually, we learn nonpolar, polar and polar with charges (basic, acidic). I'd follow Khan academy (closest to the source)

Nonpolar = hydrophobic
Polar = hydrophilic.

 

[PreMade]

Sorry for not being clear.

What I meant was some sources have tyrosine as polar/hydrophilic and other sources have it as nonpolar/hydrophobic.

I guess I will follow Khan's academy.

 

[Cawolf]

You'll see conflicting resources due to the nature of the side chain in Tyrosine.

My best advice is to consider it polar, due to the hydroxy group, for the purposes of the MCAT and USMLE. The reason there are resources that list it as non-polar is due to the aromatic ring in in the R group. This often outweighs the effect of the polar group, so it is much less soluble than other polar amino acids. Keep it simple though. If you know the R group has an alcohol, call it polar. The MCAT (and USMLE for that matter) won't be looking to trick you on something that is not agreed upon - so go with that Khan chart, it looks good to me.

 

[Mubangaeu]

I see how the polarity of Tyrosine can be confusing but I agree with Cawolf, keep it simple and go with POLAR. Because of the OH group, almost ALL of the MCAT books I've looked at classify Tyrosine as POLAR ( Hydrophilic).

 

[Mubangaeu]

One approach that helps in determining whether or not an Amino acid is polar or non-polar is looking at the FUNCTIONAL GROUPS at the end. For example, in Tyrosine, the AROMATIC RING is located WITHIN the molecule, as a result, it is 'hidden' from the outside environment. The HYDROXYL GROUP, on the other hand, is at the end of the AA chain, and exposed to the outside environment, making the AA POLAR.