The structural formulas of the amino acids are identical EXCEPT for the  the R group (side-chain).   alpha carbon.   amino group.   carboxyl group.

The structural formulas of amino acids are indeed identical except for the R group, also known as the side chain. Here's a step-by-step explanation:

1. Amino acids are organic compounds composed of an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a distinctive R group (side chain) all attached to a central carbon atom, also known as the alpha carbon.

2. The amino group, carboxyl group, and the hydrogen atom are common to all amino acids. They form the constant part of the amino acid structure.

3. The R group, or side chain, varies from one amino acid to another. It can range from a single hydrogen atom (as in glycine) to more complex and larger groups. This variation in the R group is what gives each of the 20 standard amino acids its unique properties.

4. Therefore, when comparing the structural formulas of amino acids, they are identical except for the R group (side-chain). The alpha carbon, amino group, and carboxyl group are the same in all amino acids.