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.
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.