How do you figure out whether an amino acid is hydrophobic or hydrophilic? (other than memorization) I know that it has something to do with the R groups of the amino acids, and that polar molecules are hydrophilic, while nonpolar molecules are hydrophobic, but that's about it. Please give a simple answer, I don't need too much information other than an easy way to tell.
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Does the side chain contain any Nitrogen (N), Oxygen (O), or Sulfur (S) atoms? If it does, then chances are high that this particular R-group is polar (although it may not be charged).
The converse is also true, if the R-group lacks any of those three atoms then chances are high that the side chain is polar. There are exceptions; Methionine has a Sulfur, but is quite hydrophobic (non-polar). Tryptophan has a nitrogen but is non-polar.