In sickle-cell disease, as a result of a single amino acid change, the mutant hemoglobin tetramers associate with each other and assemble into large fibers. Based on this information alone, we can conclude that sickle-cell hemoglobin exhibits:
altered primary structure.
altered secondary structure.
altered tertiary structure.
altered quaternary structure.
altered primary structure and altered quaternary structure; the secondary and tertiary structures may or may not be altered.