Proteins have _ levels of organization.

Explanation

The four levels of protein structure are: Primary structure: The linear sequence of amino acids in a protein.Secondary structure: Local folding into structures such as alpha helices and beta sheets, stabilized by hydrogen bonds.Tertiary structure: The overall three-dimensional shape of a single polypeptide chain, stabilized by various interactions between side chains.Quaternary structure: The arrangement of multiple polypeptide chains into a functional protein complex. Not all proteins have quaternary structures, but those that do, like hemoglobin, require this level of organization.Options A and B are incorrect because they do not account for all the structural levels up to quaternary. Option D is incorrect because there is no recognized fifth level of protein structure.