Active Site Defined by Primary Structure

Steps:

• Define active site as the enzyme region binding substrate for catalysis.
• Recall primary structure as linear amino acid sequence of the enzyme.
• Note that primary structure folds into secondary, tertiary, and quaternary structures.
• Conclude that folding determines active site's precise 3D shape and specificity.

Why D is correct:

• Primary structure (amino acid sequence) dictates higher-level folding, directly shaping the active site's configuration per protein folding principles.

Why the others are wrong:

• A: Active site shape is specific but can flex via induced fit, not always rigidly fixed.
• B: Active site lowers activation energy for reaction, not product's total energy.
• C: Active site forms temporary chemical bonds (e.g., hydrogen bonds) with substrate to stabilize transition state.

Final answer: D