Enzyme activity peaks at optimal pH in a bell-shaped curve

Steps:

• Enzymes function best at a specific optimal pH where the active site is correctly shaped.
• Deviations from optimal pH alter enzyme ionization or cause denaturation, reducing reaction rate.
• The typical graph plots rate versus pH as a symmetrical or asymmetrical bell curve with a maximum.
• Graphs 2 and 4 match this pattern, while others show linear, flat, or monotonic trends unsuitable for pH effects.

Why C is correct:

• Bell-shaped curves reflect the biochemical principle that enzyme catalysis is maximal at optimal pH due to balanced protonation of amino acid residues in the active site.

Why the others are wrong:

• A: Includes graph 1, likely linear or rising, ignoring pH's bidirectional inhibition.
• B: Includes graphs 1 and 3, which fail to show the characteristic peak and decline.
• D: Includes graph 3, probably monotonic or flat, not capturing pH optima.

Final answer: C