I agree, this can get very confusing!

When you are asked to classify amino acids based on polarity, YES, you focus only on the R-group. That is because all amino acids have the same basic structure, and differ only in this group! https://s3-us-west-2.ama...936/figure-03-04-01.jpeg

Here is a great summary of the polarity of amino acids: https://s3-us-west-2.ama...5938/figure-03-04-02.png

Like you've said with glycine, the R group is an H atom, which is non-polar. So, the unique part that makes the amino acid glycine (the glycine residue) is non-polar.

But, when we consider glycine as an entire molecule (taking into account the rest of the protein structure), we can see that it consists of a C-NH2 group (polar), a CH2 group (non-polar), and a COOH group (polar). Both of these groups (C-NH2 and COOH) are capable of gaining formal charges under the right conditions.

https://lh3.googleuserco...SLT1i65pxxAWH-r1RwqT0cds