28. What structure(s) determines the specific shape of a protein? Primary, Secondary, or Tertiary.

The specific shape of a protein is primarily determined by its **tertiary structure**. The tertiary structure refers to the overall three-dimensional arrangement of the protein's polypeptide chain, which is influenced by various interactions among the side chains (R groups) of the amino acids, such as hydrogen bonds, ionic bonds, hydrophobic interactions, and disulfide bridges. While the **primary structure** (the sequence of amino acids) is crucial because it dictates how the protein will fold, and the **secondary structure** (local folding patterns like alpha helices and beta sheets) contributes to the overall shape, it is the tertiary structure that defines the final, functional shape of the protein. In some cases, proteins may also have a **quaternary structure**, which involves the assembly of multiple polypeptide chains, but the question specifically asks about the shape of a single protein molecule.