The correct statement about peptides and proteins is

Tertiary structure of proteins has two or more polypeptide subunits.

Only the proteins having a quaternary structure are biologically active.

In $\displaystyle \beta$-pleated sheet structures, peptide chains are held together by intermolecular hydrogen bonds.

In $\displaystyle \alpha$-helices, the polypeptide chain is twisted into a left-handed screw (helix) through intramolecular hydrogen bonds.