Which statement accurately describes how pH affects enzyme activity?

• A. Enzyme activity at pH 14 for all enzymes
• B. Enzyme activity is unaffected by pH
• C. Enzyme activity decreases as pH moves away from the optimum and extreme pH can denature the enzyme
• D. Enzyme activity increases when pH moves away from the optimum

Answer: (C)

pH affects enzyme activity because enzymes rely on their precise 3D shape to catalyze reactions, and that shape depends on ionization states of amino acids and the strength of hydrogen and ionic bonds holding the structure together. Each enzyme has an optimum pH at which its active site is most complementary to the substrate. When the pH moves away from this optimum, changes in charge and bonding disrupt the active site's geometry, making binding less efficient and slowing the reaction. At extreme pH values, the protein can even unfold, permanently denaturing it and eliminating activity. This is why enzyme activity typically decreases as pH departs from the optimum, and extreme pH can denature the enzyme.

Options proposing pH 14 for all enzymes, claiming no effect from pH, or claiming activity increases as pH moves away from the optimum ignore how enzyme shape and stability depend on pH and are not universally true across enzymes. Different enzymes have different pH optima, reflecting their specific environments and roles.