GCSE · Biology · Edexcel · Spec 1BI0
Enzyme denaturation
Bend a lock so its hole changes shape and the key won’t go in, even though the key is fine. Two very different things can do that to an enzyme.
Look at the lock
View
Explore
Flip the view and watch what happens to the pocket.
Shape intact, substrate fits, enzyme–substrate complex forms.
Switch between the two views, then tap the dashed regions to see what each one is doing.
WHAT YOU'VE LEARNED
A quick recap of today's lesson.
How too much heat or the wrong pH ruins an enzyme’s active site — and why it stays ruined
What you need to know
- An enzyme’s active site has a specific shape that is complementary to its substrate. That shape depends on how the enzyme’s protein chain is folded and held in place by bonds within the molecule.
- Denaturation is a change in the shape of the active site so that the substrate no longer fits. A denatured enzyme cannot form enzyme–substrate complexes, so it can no longer catalyse its reaction.
- Temperatures above the optimum denature an enzyme: the extra energy makes the molecule vibrate more, which breaks the bonds holding its shape.
- A pH far from the optimum, too acidic or too alkaline, also denatures an enzyme because it disrupts the bonds that hold the enzyme in shape.
- Denaturation is permanent. Low temperatures do not denature enzymes; they only slow reactions because molecules move more slowly and collide less often.
The big picture
An enzyme works because its active site has a specific shape that matches its substrate, and that shape depends on the enzyme’s folded protein chain being held in place by bonds. Temperatures above the optimum, or a pH far from the optimum, disrupt those bonds. The active site changes shape, the substrate no longer fits, no enzyme–substrate complex can form and the enzyme can no longer catalyse its reaction. This is denaturation, and it is permanent. Low temperatures do not denature enzymes; they only slow reactions down.
Key points
Worked example
Problem
Explain why an enzyme stops catalysing its reaction when it is in a solution with a pH far from its optimum.
⚠ Watch out
Jumping straight from ‘it’s too hot’ (or ‘the pH is wrong’) to ‘so the enzyme stops working’. The explanation lives in the middle of the chain: say what happens to the bonds, then to the active site, then to the fit of the substrate.
Memory hook
Bonds break, site bends, key won’t fit. And a bent lock stays bent. (Where the lock-and-key picture breaks down: a real active site is held in shape by bonds inside a folded chain, which is why disrupting those bonds is what changes it.)
Check yourself
An enzyme has been denatured by heat, then cooled right down. Does its active site return to its original shape? (No: denaturation is permanent.)
Flashcards
(9)What gives an enzyme’s active site its shape?
What does it mean to say the active site is complementary to the substrate?
What is denaturation?
What is an enzyme–substrate complex?
What does extra heat energy do to an enzyme molecule above its optimum temperature?
How can pH denature an enzyme?
Does cooling a denatured enzyme, or restoring its optimum pH, bring it back?
Do low temperatures denature enzymes?
Put in order: active site changes shape, bonds disrupted, substrate no longer fits, no complex forms.
Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.
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