Mutations and Their Effect on Proteins · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Small DNA changes, big protein effects

Science · Genetics & Evolution · ages 15-16
Name ______________________   Date ____________

  1. Why does deleting one base scramble everything after it?

    • Every later triplet regroups around the gap
    • Repair enzymes delete the rest
    • The cell runs out of bases

  2. What can a single base substitution do?

    • Only ever destroy the protein
    • Leave the acid, change the acid, or insert a stop
    • Always shift the reading frame

  3. Repair enzymes fix most copying slips before they lock in as mutations.

    Circle one:   True   False

  4. Using the mini table, what does changing CAA to UAA do?

    • Ends the chain early at a stop
    • Leaves the protein unchanged
    • Adds one extra acid

  5. Using the mini table, what does changing CAA to CAG do?

    • Shifts the whole frame
    • Stops the chain early
    • Nothing visible, since both mean glutamine

  6. Two mutations strike one enzyme: one in the active site, one far along the chain. Which matters more, and why?

    • Both matter exactly equally
    • The far one, since it is bigger
    • The active site one, since the target must fit there

  7. One base in a thousand changes an enzyme active site and the enzyme dies. How can so little DNA do so much?

    • The single acid reshapes the dock the target must fit
    • The cell deletes the whole gene in panic
    • Mutagens multiply the change a thousandfold

  8. A student claims a silent CAA to CAG swap will stop the enzyme working. What is the error?

    • CAG is a stop triplet
    • The acid is unchanged, so the shape and job survive
    • Silent swaps always shift the frame
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Answer key

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

Small DNA changes, big protein effects W1-mt_dTOQH3vGSz-s1

  1. Every later triplet regroups around the gap · The frame shifts, so all downstream triplets spell different acids.
  2. Leave the acid, change the acid, or insert a stop · One swap has three possible outcomes depending on the new triplet.
  3. True · Proofreading catches nearly everything, which is why mutations stay rare.
  4. Ends the chain early at a stop · UAA is a stop triplet, so the protein is cut short.
  5. Nothing visible, since both mean glutamine · Both triplets name glutamine, so the change is silent.
  6. The active site one, since the target must fit there · Shape at the working face decides whether the enzyme grips its target.
  7. The single acid reshapes the dock the target must fit · One wrong acid in the working face breaks the fit for the target.
  8. The acid is unchanged, so the shape and job survive · With glutamine still in place, folding and function carry on.
Worksheet · LightMySky