Which property of enzymes is most directly altered by changes in temperature and pH?

• A. Three-dimensional shape.
• B. Primary structure.
• C. Active site sequence.
• D. Genetic code.

Answer: (A)

Temperature and pH affect how an enzyme folds and holds its shape. The three-dimensional arrangement of the protein creates the active site, where substrates bind. When temperature rises or pH shifts, noncovalent interactions like hydrogen bonds and ionic bonds can break or rearrange, causing the enzyme to unfold or change shape. That change in shape directly alters the geometry of the active site, so substrate binding and catalytic efficiency are affected.

The amino acid sequence, or primary structure, isn’t altered by these conditions under normal circumstances, and the genetic code that specifies that sequence remains the same. The other terms describe aspects that are not immediately changed by temperature or pH in the same way the overall fold is.