Enzyme Kinetics: Vmax and the Michaelis Constant · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Reading the curve that levels off

Science · Organisms & Life Processes · ages 16-18
Name ______________________   Date ____________

  1. How do you find Km on the same curve?

    • Read the highest rate on the curve
    • Find half of Vmax, move across to the curve, then read the substrate below
    • Count the active sites one by one

  2. How do you read Vmax from a rate against substrate curve?

    • From the flat top where the rate levels off
    • From the steep slope at the start
    • From the substrate axis at zero

  3. Vmax is reached when every active site of the enzyme is busy.

    Circle one:   True   False

  4. Enzyme A has Km 2 and enzyme B has Km 8. Which binds its substrate more tightly?

    • Enzyme A, since half speed arrives with less substrate
    • Enzyme B, since 8 is bigger
    • Both bind exactly as tightly

  5. Why is the curve steep at low substrate amounts?

    • The enzyme changes shape to work slower
    • Substrate molecules block each other
    • Most sites sit empty, so each extra molecule quickly finds a home

  6. An enzyme has a Vmax of 80 rate units. What rate is exactly half of Vmax?

    Answer: ______________

  7. A student says Km tells you the ceiling rate of the enzyme. What is wrong?

    • Curves have no ceiling at all
    • Km can only be read from tables
    • Km measures the grip while Vmax alone gives the ceiling

  8. A student keeps adding substrate past saturation and expects the rate to keep climbing. What is wrong?

    • Substrate poisons the enzyme at once
    • All sites already work full time, so extras must queue with no gain
    • Vmax rises forever with more substrate
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Answer key

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

Reading the curve that levels off W1-mt_ooF8eZ1Gzy-s1

  1. Find half of Vmax, move across to the curve, then read the substrate below · Km is the substrate amount that buys exactly half of Vmax.
  2. From the flat top where the rate levels off · The ceiling is the fastest rate, reached when every site is busy.
  3. True · Full occupancy is the ceiling, since no site can work faster than full time.
  4. Enzyme A, since half speed arrives with less substrate · Smaller Km means half speed with less substrate, which is tighter binding.
  5. Most sites sit empty, so each extra molecule quickly finds a home · Empty sites grab newcomers at once, so the rate jumps.
  6. 40 · Half of 80 is 40, the rate you carry across to find Km.
  7. Km measures the grip while Vmax alone gives the ceiling · Height and grip are two readings, and Km is the grip one.
  8. All sites already work full time, so extras must queue with no gain · Saturation caps the rate, so extra substrate only lengthens the queue.
Worksheet · LightMySky