Here's why:

* Enzymes are proteins, and proteins have specific three-dimensional shapes that are essential for their function.

* Extreme pH or temperature conditions disrupt the weak bonds (like hydrogen bonds) that hold the protein's shape together.

* This disruption causes the protein to unwind and change shape, losing its specific three-dimensional structure.

* This loss of structure is called denaturation, and it renders the enzyme inactive because it can no longer bind to its substrate properly.

Think of it like a puzzle: the enzyme's shape allows it to fit perfectly with its substrate. Denaturation is like taking the puzzle apart, making it impossible to put it back together correctly.