As you want a professional answer, I will recommend my viewpoint without any doubt.Amino acids can be classified by R group. The polarity of the R groups varies widely, from nonpolar and hydrophobic (water-insoluble) to highly polar and hydrophilic (water-soluble). Glycine has got a nonpolar and aliphatic R group. Although it is formally nonpolar, its very small side chain makes no real contribution to hydrophobic interactions.参考资料:《Lehninger Principles of Biochemistry》