The correct statement about peptides and proteins is

In $\alpha$-helix structure, the polypeptide chain is twisted into a right-handed screw, not left-handed.

Tertiary structure represents the overall folding of a single polypeptide chain. Proteins with two or more polypeptide subunits exhibit quaternary structure.

Proteins can be biologically active in their tertiary structure as well, so it is incorrect to say only proteins with quaternary structure are active.

In $\beta$-pleated sheet structures, all peptide chains are stretched out to nearly maximum extension and laid side by side, held together by intermolecular hydrogen bonds.

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