Question

Complete the following statement.
The quaternary structure of a protein

• A. Consists of four subunits, hence the name quaternary.
• B. Is unrelated to the function of the protein.
• C. May be either $\alpha$ or $\beta$ and depends on the primary structures of the subunits.
• D. Depends on the covalent bonding among the subunits.

Answer 1

The correct option is C May be either $\alpha$ or $\beta$ and depends on the primary structures of the subunits.

Conceptually, protein structure can be understood at four levels. They are primary, secondary, tertiary and quaternary.
Primary structure includes all the covalent bonds between amino acids and is normally defined by the sequence of peptide-bonded amino acids and locations of disulphide bonds. The relative spatial arrangement of the linked amino acids is unspecified.
Secondary structure refers to regular recurring arrangements of space of adjacent amino acid residues in a polypeptide chain.
Tertiary structure refers to the spatial relationship among all amino acids in a polypeptide chain; it is the complete three dimensional structure of a polypeptide.
Proteins with several polypeptide chains have one more level of structure called the quaternary structure, which refers to the spatial relationship of the polypeptides or subunits within the membrane. The arrangement of proteins and protein subunits in three dimensional complexes or quaternary structure is stabilized and guided by multiple non covalent interactions. The two most common quaternary structures of multisubunit proteins are $\alpha$-helices in globular proteins and $\beta$-sheets in fibrous proteins. The functional properties of multi-subunit proteins depends on the quaternary structure.