Final answer:
Changes in pH above or below an enzyme's optimal range can negatively affect its function by altering its active site and potentially leading to the enzyme's denaturation, which is often irreversible. Optimal pH levels are crucial for enzyme activity. So the correcct option is D.
Step-by-step explanation:
When the pH level moves above or below an enzyme's optimal pH, the enzyme's function can be affected, predominantly in a negative way. For enzymes, each has a specific pH range in which they function most effectively. Deviations from this pH range can lead to changes in the enzyme's structure, ultimately affecting its activity. When the pH shifts significantly, enzymes can denature, leading to a loss of their three-dimensional structure which is essential for their activity. This denaturation is often irreversible, especially if the change in pH is extreme.
Optimal pH is essential for maintaining the proper shape of the enzyme's active site, which is necessary for the substrate to bind effectively and for the enzyme to catalyze reactions. The active site's amino acid residues have distinct acidic and basic properties that are affected by pH changes, influencing how well substrates fit. If the pH is altered significantly, the change can impair the binding of substrates and reduce the rate of enzyme-catalyzed reactions, thereby affecting the enzyme's functionality. It's also worth noting that slight alterations in pH may only temporarily affect the enzyme's function, but harsher pH conditions can lead to permanent enzyme denaturation.
In response to the provided question about the effect of pH changes on enzyme function, the correct answer is D. Enzyme denatures.