Enzyme Action and the Active Site · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

One shape, one job

Science · Organisms & Life Processes · ages 14-16
Name ______________________   Date ____________

  1. What is the active site?

    • The energy barrier that starts a chemical reaction
    • The pocket where a substrate binds and reacts
    • The product molecule released after the reaction

  2. What is an enzyme?

    • A catalyst, usually a protein, that speeds a reaction
    • A substrate molecule that is consumed during a reaction
    • A digestion product made after food is chemically broken down

  3. The reaction uses up the enzyme.

    Circle one:   True   False

  4. What happens to the enzyme once its reaction finishes?

    • It is used up like fuel during the reaction
    • It changes into the product made by the reaction
    • It is unchanged and works again

  5. Why does salivary amylase act on starch rather than protein?

    • Its active site fits starch better than protein
    • Protein is too strong for any enzyme to break apart
    • Starch blocks every protein-digesting enzyme from binding

  6. How do enzymes speed up reactions?

    • By adding heat to every cell where reactions happen
    • By lowering activation energy
    • By changing the products made by the reaction

  7. An active site changes shape after a mutation. What is most likely?

    • The rate rises because every substrate fits much better
    • The rate stays the same because shape does not matter
    • The rate falls because the substrate fits less well

  8. Leo says an active site is a rigid pocket that never changes shape when a substrate binds. Which idea corrects him?

    • The active site grows stronger so it can force any substrate into place
    • The site shifts a little as the substrate binds, giving a closer fit
    • The active site only changes shape after the products have left the enzyme
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Answer key

For grown-ups. Fold this page away before handing over the rest.

One shape, one job W1-mt__ozLTPNN0H-s1

  1. The pocket where a substrate binds and reacts · The active site is the enzyme pocket where the substrate binds and the reaction is helped.
  2. A catalyst, usually a protein, that speeds a reaction · Enzymes are catalysts, usually proteins, and a catalyst is not used up by the reaction it speeds.
  3. False · The enzyme is released unchanged after the reaction and can catalyse another reaction.
  4. It is unchanged and works again · Catalysts are not consumed, so the enzyme is free for the next substrate.
  5. Its active site fits starch better than protein · Specificity comes from the active site's shape and chemistry. Salivary amylase has a better fit for starch than for protein.
  6. By lowering activation energy · Enzymes lower the starting push, called activation energy, so reactions run faster.
  7. The rate falls because the substrate fits less well · A changed active site can make the substrate fit less well, so the reaction rate usually falls.
  8. The site shifts a little as the substrate binds, giving a closer fit · In induced fit, the active site shifts a little as the substrate binds. This gives a closer working fit, so the site is not a rigid, unchanging pocket.
Worksheet · LightMySky