Active Site Formation via Protein Folding Levels

Steps:

• Primary structure is the linear amino acid sequence, which sets the foundation but does not position residues spatially for the active site.
• Secondary structure forms local folds like alpha helices and beta sheets, positioning nearby residues correctly.
• Tertiary structure folds the chain into a 3D shape, bringing distant residues together to create the active site.
• Quaternary structure assembles multiple polypeptide chains, allowing active site formation across subunits in multisubunit enzymes.

Why B is correct:

• Active site requires spatial arrangement of residues via secondary (local motifs), tertiary (overall fold), and quaternary (subunit interactions) structures, per protein folding hierarchy.

Why the others are wrong:

• A includes primary (sequence alone lacks 3D positioning) and excludes quaternary (needed for multisubunit enzymes).
• C excludes tertiary (essential for 3D pocket formation).
• D excludes all higher levels (ignores folding necessary for active site).

Final answer: B