In proteins, what structural feature primarily differentiates one amino acid from another?

In biochemistry, what is the monomer unit of a protein called?

In a standard amino acid, what does the R group represent?

In the general structure of an amino acid, what does the R group represent?

In proteinogenic amino acids, what primarily distinguishes one amino acid from another?

In a standard amino acid (the building block of proteins), which set of functional groups is always present in the backbone structure?

In proteins, what structural feature primarily makes one amino acid different from another?

Which hormone is synthesized from a single amino acid residue (i.e., derived from one amino acid) rather than from a peptide chain?

In a standard amino acid, which functional group is always acidic (able to donate a proton) under typical aqueous conditions?