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AP Biology — Unit 6 — Mutations — Drill 26

Drill 26 ·

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About This Drill

AP Biology — Unit 6 — Mutations — Drill 26 is a practice drill. It contains 5 original questions created by Brian Stewart, a Barron's test prep author with over 20 years of tutoring experience.

Analyze the effects of different point mutation types on protein structure and function, using experimental data to evaluate claims about mutation mechanisms.

Passage

A genetics laboratory examines the effects of three point mutations in a gene encoding a 120-amino-acid enzyme in human cells. The mutations occur at the same position in the DNA but produce different changes to the mRNA codon at position 47. The wild-type codon at position 47 is GAG (glutamic acid, a negatively charged amino acid). The enzyme's active site requires a negatively charged residue at position 47 for substrate binding.
Mutation Effects at Position 47:
Wild-type: Codon GAGAmino Acid: Glu (negatively charged)Enzyme Activity: 100%
Mutation A: Codon GAG->UAGAmino Acid: Glu->StopEnzyme Activity: 0%
Mutation B: Codon GAG->GAAAmino Acid: Glu->GluEnzyme Activity: 98%
Mutation C: Codon GAG->AAGAmino Acid: Glu->Lys (positively charged)Enzyme Activity: 4%

Questions in This Drill

  1. What type of mutation is represented by Mutation B (GAG->GAA)?
  2. Based on the table, which conclusion is most directly supported by comparing the effects of the stop codon mutation and the charge-reversal mutation at position 47?
  3. A researcher claims that the 4% residual activity in the charge-reversal mutation is due to the positive charge of lysine partially compensating for the loss of negative charge at position 47. Which additional experiment would most directly test this claim?
  4. The stop codon mutation at position 47 produces a truncated polypeptide of 46 amino acids. A student predicts this truncated protein will have no enzymatic activity. Which reasoning best supports this prediction?
  5. Which mutation type, if it occurred earlier in the coding sequence rather than at position 47, would most likely affect the largest number of downstream amino acids?