Normal hemoglobin is a tetramer, consisting of two molecules of hemoglobin and two molecules of hemoglobin. 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 .
a. only altered primary structure only altered tertiary structure
b. only altered quaternary structure
c. altered primary structure and altered quatermary structure
d. the secondary and tertiary structures may or may not be altered