What is a prosthetic group? Select the single best answer. a nonprotein group attached to a protein, but not required in order for the protein to function a second protein group required in order for a protein to function an enzyme group required in order for a protein to function an amino acid group required in order for a protein to function an amino acid group attached to a protein, but not required in order for the protein to function a second protein group attached to a protein, but not required in order for the protein to function a nonprotein group required in order for a protein to function