Enzyme Inhibition and Metabolic Control · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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Read what inhibitors do to enzymes

Science · Organisms & Life Processes · ages 17-18
Name ______________________   Date ____________

  1. In the pure non-competitive model, where can the inhibitor bind?

    • At the active site, excluding every substrate molecule
    • Away from the active site, allowing substrate to bind
    • On the substrate, preventing its contact with the enzyme

  2. At fixed enzyme and inhibitor concentrations, what does reversible competitive inhibition do to Vmax and apparent Km?

    • Vmax stays constant; apparent Km increases
    • Vmax increases; apparent Km stays constant
    • Vmax decreases; apparent Km also decreases

  3. Finding that an inhibitor binds away from the active site is enough to prove pure non-competitive inhibition.

    Circle one:   True   False

  4. An inhibitor binds only to the enzyme-substrate complex. Vmax and apparent Km both decrease by the same factor. Which inhibition type fits?

    • Competitive inhibition
    • Uncompetitive inhibition
    • Pure non-competitive inhibition

  5. Under otherwise identical conditions, an inhibitor leaves Vmax at 24 rate units but moves the substrate concentration giving 12 rate units from 2 to 6 mmol/L. Which model fits?

    • Pure non-competitive inhibition
    • Uncompetitive inhibition
    • Competitive inhibition

  6. As substrate concentration rises at fixed inhibitor concentration, why can competitive inhibition be overcome but pure non-competitive inhibition cannot?

    • Substrate excludes competitive inhibitor binding, but not pure non-competitive binding
    • Substrate breaks competitive inhibitor molecules apart, but stabilises pure non-competitive molecules
    • Substrate dilutes competitive inhibitor concentration, but concentrates pure non-competitive inhibitor

  7. ATP availability rises while other conditions stay suitable. What feedback response can occur in cellular respiration?

    • Some regulated enzymes slow, reducing further ATP production
    • Every respiration enzyme speeds up, increasing further ATP production
    • All enzyme activity stops permanently, preventing further ATP production

  8. A pathway's final product slows an earlier purified enzyme. Removing the product restores activity without replacing the enzyme. Substrate concentration, temperature and pH are unchanged. Which explanation best fits?

    • The product blocks substrate binding by lowering the solution's pH
    • The product irreversibly inactivates enzyme molecules until they are replaced
    • The product binds reversibly, reducing activity while it remains bound
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Answer key

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

Read what inhibitors do to enzymes W1-mt_8VYolkJ_wR-s1

  1. Away from the active site, allowing substrate to bind · The inhibitor binds at a separate site. Substrate can still bind, but inhibitor-bound enzyme cannot catalyse the reaction.
  2. Vmax stays constant; apparent Km increases · More substrate reduces competition from the inhibitor, so Vmax is unchanged. More substrate is needed for half of Vmax, so apparent Km increases.
  3. False · Other inhibition models also allow separate-site binding. Pure non-competitive inhibition requires the specific equal-affinity model and its unchanged-Km, lower-Vmax pattern.
  4. Uncompetitive inhibition · Binding only to the enzyme-substrate complex identifies uncompetitive inhibition. Its proportional decrease in both parameters agrees with that model.
  5. Competitive inhibition · Half of 24 is 12. Apparent Km rises from 2 to 6 mmol/L while Vmax stays unchanged, matching competitive inhibition.
  6. Substrate excludes competitive inhibitor binding, but not pure non-competitive binding · Competitive binding is mutually exclusive, so more substrate reduces inhibitor occupancy. Pure non-competitive inhibitor can bind enzyme with substrate bound, leaving a lower Vmax.
  7. Some regulated enzymes slow, reducing further ATP production · High ATP availability can inhibit some regulatory enzymes and reduce further production. It does not permanently stop every enzyme.
  8. The product binds reversibly, reducing activity while it remains bound · Recovery after product removal, using the same enzyme under unchanged conditions, supports reversible feedback inhibition. A pH change or replacement of damaged enzyme does not explain these observations.
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