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.

Altered primary structure.

Explanation:

Proteins are formed by chains of amino acids, which constitutes their primary structure. In sickle-cell disease, there is a single amino acid exchange. Therefore, the primary structure of the protein is altered, and because of this hemoglobin form long fiber that clog arteries.

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