What happens to most enzymes when the temperature exceeds their optimal range?

• A. They work more efficiently
• B. They become denatured and lose activity
• C. They become more active
• D. They experience no changes in activity

Answer: (B)

When the temperature exceeds an enzyme's optimal range, the enzyme typically becomes denatured, which results in a loss of its functional activity. Enzymes are proteins, and their activity depends on their three-dimensional structure, which is sensitive to temperature changes.

At higher temperatures, the increased kinetic energy can disrupt the hydrogen bonds and other interactions that maintain the enzyme's unique shape. This leads to alterations in the active site—the region of the enzyme where substrates bind and reactions occur. As the structure is compromised, the enzyme’s ability to bind to its substrate decreases, significantly diminishing its catalytic activity.

While some enzymes may have a degree of thermal stability and can operate effectively at elevated temperatures, those that exceed their optimal range are generally at risk of denaturation and loss of function. Therefore, the correct answer reflects the general behavior of most enzymes when exposed to high temperatures beyond their optimal range.