Cold slows an enzyme, but too much heat unfolds it
- The idea
- Predict
- See it
- Why
- Check
The idea
“Cold and heat harm an enzyme the same way, so both losses reverse or neither does.”
On a temperature graph the rate falls at both ends, so the two drops look like the same harm. Only one of them is damage.
The short version
The mistake: Cold and heat harm an enzyme the same way, so both losses reverse or neither does.
What's actually true: Cold just slows the molecules, so the rate comes back on warming. Too much heat unfolds the enzyme, and that usually lasts.
- Below the optimum, molecules move slower and collide less often, with less energy. The enzyme keeps its shape, so warming it brings the rate back.
- Above the optimum, heat breaks the hydrogen bonds and other weak interactions that hold the enzyme folded. It denatures, and its active site no longer fits the substrate.
- Cooling usually doesn't refold a denatured enzyme, so it stays tangled and inactive.
On the exam: Test it back at a normal temperature. Slowing from cold comes back. Unfolding from heat usually doesn't.