Enzyme Action and the Active Site
An enzyme speeds up one reaction because its active site fits one substrate shape. Covers the lock and key model, specificity, and why an enzyme is not used up by the reaction it runs.
What a learner can do afterwards
- Explains specificity in terms of the shape of the active site rather than the strength of the enzyme.
- States what happens to an enzyme once its reaction has finished.
- Predicts what a change in active site shape does to the reaction.
1 · Read
Enzymes are protein catalysts that speed up reactions without being used up, so the enzyme in saliva can work on each bite of bread. Each enzyme holds its reactants, called substrates, in a pocket named the active site. The enzyme lowers the push needed to start the reaction, called activation energy.
The active site fits one substrate shape, like a lock fits one key, then hugs it closer to make it react. The starch-breaking enzyme grips starch and ignores protein completely. After the reaction the enzyme walks away unchanged and works again.
Shape decides the job, so a warped active site stops the work. If the pocket changes shape it no longer grips its substrate and the rate falls to nothing. That is why each enzyme runs only its own reaction.
When asked about specificity, talk about shape, never strength. Say the site fits one substrate, the enzyme is not used up, and a changed site means a stopped reaction.
The active site shape picks one substrate, speeds its reaction, and survives to work again.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.