1. A change that makes a polypeptide defective has been discovered in its amino acid sequence. The normal and defective amino acid sequences are shown below. Researchers are attempting to reproduce the conditions and events that resulted in this defective amino acid sequence. Which statement is the best prediction of the conditions and events that the researchers will most likely find produced the defective polypeptide? (A) During DNA replication, there was a deletion of a single nucleotide that codes for lysine (Lys), resulting in translation of a polypeptide without the Lys amino acid. (B) During mrna transcription, the codon that codes for Lys was removed from the transcript, resulting in translation of a polypeptide without the Lys amino acid. (C) During translation, the transfer RNA matched an incorrect amino acid with the mrna strand, resulting in a defective polypeptide. (D) During protein folding, one of the amino acids was mistakenly removed during the final stage of protein assembly, resulting in a defective polypeptide. Page 1 of 6
2. A transfer RNA (trna) molecule for phenylalanine is shown in the diagram below, and an mrna codon chart is provided as a reference. Page 2 of 6
A yeast cell has a defective enzyme that attaches the lysine amino acid (Lys), instead of a phenylalanine amino acid (Phe), to trnas with the anticodon AAG. Which statement describes the most likely result in the cell? (A) None of the proteins in the cell will contain phenylalanine, because the defective trna molecule will not transcribe the appropriate DNA sequence into a phenylalanine amino acid. (B) Proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUC, because of the defective enzyme. (C) The cell will correct the defect, because other enzymes will attach phenylalanine to trnas with lysine-specifying anticodons to compensate for the defective enzyme. (D) The cell will adapt and change any mrna sequences that include the codon UUC to the codon UUU, because the codon UUU also codes for phenylalanine. Page 3 of 6
3. The diagram below shows a segment of an mrna molecule and the polypeptide sequence that it produces during translation. The table below the diagram shows how each codon is translated during protein synthesis in the ribosome. A mutation in the original DNA sequence occurs that results in the deletion of a uracil nucleotide from the mrna molecule, as shown in the diagram below. Page 4 of 6
Which statement best predicts the resulting change in the polypeptide? (A) The third amino acid will be leucine instead of phenylalanine, because the missing nucleotide only affects the third codon. (B) The third and fourth amino acids will be leucine and alanine instead of phenylalanine and glycine, because the missing nucleotide only affects the third and fourth codons. (C) The third, fourth, and fifth amino acids will be changed and the mrna will continue to be translated, because the stop codon will be changed to a coding triplet. (D) The third amino acid will remain the same despite the deletion, because the first two nucleotides in the codon ultimately determine which amino acid the codon is translated into. Page 5 of 6
4. The diagrams below show transcription and translation in a prokaryotic cell and in a eukaryotic cell. A eukaryotic gene is inserted into the genome of a prokaryotic cell. Which statement best predicts how transcription and translation of the genetic information would be affected? (A) Transcription and translation of the eukaryotic gene would produce a smaller protein in the prokaryotic cell, because prokaryotes utilize fewer amino acids than eukaryotic cells do. (B) Many more copies of the eukaryotic protein would be produced, because transcription and translation occur at the same time, and are therefore much faster in prokaryotic cells. (C) Transcription and translation of the eukaryotic gene would produce the same protein in the prokaryotic cell, because the process of protein synthesis is the same in all organisms. (D) The eukaryotic protein produced in the prokaryotic cell would have many additional amino acids, because non-coding regions of nucleic acids are not removed in prokaryotic cells. Page 6 of 6