Changing temperature or pH can change an enzyme’s shape , especially the shape of its active site, so the substrate no longer fits properly and the enzyme works more slowly or stops working altogether.

Quick Scoop: What actually happens?

  • Enzymes are proteins folded into a very specific 3D shape, with an active site that fits the substrate like a key in a lock.
  • Temperature and pH help hold that shape together by influencing hydrogen bonds, ionic bonds, and other interactions in the protein.
  • When conditions move too far from the enzyme’s “optimum” (best) temperature or pH, those bonds are disrupted and the protein’s shape changes.
  • If the active site changes shape, the substrate can’t bind properly, fewer enzyme–substrate complexes form, and the reaction rate drops.
  • In extreme cases, the enzyme denatures: the shape change is so large that the enzyme becomes permanently inactive.

A simple way to picture it

Imagine scissors (the enzyme) cutting paper (the substrate).
If you bend or melt the scissors, the blades no longer meet correctly. They are still “there,” but they can’t cut paper.
Likewise, when temperature or pH alters an enzyme’s shape, the active site no longer matches the substrate, so the enzyme can’t catalyze the reaction effectively.

Bottom note: Information gathered from public forums or data available on the internet and portrayed here.

TL;DR: Changing temperature or pH can distort the enzyme’s active site, so the substrate no longer fits; this reduces or stops the enzyme’s function by lowering reaction rate or causing denaturation.