Cell Cycle Checkpoints, Control and Cancer · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Checkpoints that guard cell division

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

  1. What does the G2 checkpoint test?

    • Whether DNA was copied fully and correctly
    • Whether the cell is large enough to start
    • Whether daughter cells have split apart

  2. What does the G1 checkpoint test before a cell may pass?

    • Whether DNA was copied correctly
    • Whether chromosomes are attached to spindle fibres
    • Whether the cell is big enough with undamaged DNA

  3. Which pair describes the two control gene families correctly?

    • Both families hold division back
    • Proto-oncogenes drive division, tumour suppressors restrain it
    • Both families drive division forward

  4. A mutation locks a proto-oncogene permanently on. What is the likely result?

    • Uncontrolled division may form a tumour
    • The cell stops dividing and repairs itself
    • The cell pauses forever at the G1 checkpoint

  5. A checkpoint finds damaged DNA that can still be repaired. What happens next?

    • The cell divides at once to dilute the damage
    • The cycle halts while repairs happen
    • The cell skips the next checkpoint as compensation

  6. Why does a cell with damaged DNA usually never reach division at all?

    • Halted for repair or ordered to die
    • Damaged DNA always fixes itself within minutes
    • Division destroys damaged DNA automatically

  7. Knocking out a tumour suppressor gene can let cells divide without control.

    Circle one:   True   False

  8. A student says a single mutation always causes cancer at once. What is wrong with this claim?

    • Mutations can never affect control genes
    • Most tumours need several control mutations stacked over years
    • Checkpoints repair every mutation without fail
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Answer key

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

Checkpoints that guard cell division W1-mt_nwNmCVnZ7O-s1

  1. Whether DNA was copied fully and correctly · G2 sits after copying, so it checks that the copy is complete and correct.
  2. Whether the cell is big enough with undamaged DNA · G1 checks size and damage. Copying is checked later at G2.
  3. Proto-oncogenes drive division, tumour suppressors restrain it · Proto-oncogenes are the accelerator and tumour suppressor genes are the brakes.
  4. Uncontrolled division may form a tumour · A stuck accelerator pushes the cell past checkpoints it should have obeyed.
  5. The cycle halts while repairs happen · A failed test pauses the cycle so repair comes before division.
  6. Halted for repair or ordered to die · The checkpoint system stops faulty cells before they can copy the fault into daughters.
  7. True · Without its brakes the cell races past checkpoints and divides wildly.
  8. Most tumours need several control mutations stacked over years · One fault is rarely enough. Tumours usually build up several broken switches over years.
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