1. The diagram below shows an error in the transcription of a DNA template to messenger RNA (mrna).

Transcription

1 1. The diagram below shows an error in the transcription of a DNA template to messenger RNA (mrna). Which statement best describes the error shown in the diagram? (A) The mrna strand contains the uracil base whereas it should contain the thymine base. This answer suggests the student may understand that uracil is not found in DNA, but does not understand that it is present in mrna because RNA contains uracil instead of thymine. (B) The mrna strand is being synthesized from left to right in the 3' should be synthesized in the 5' 3' direction. 5' direction whereas it This answer suggests the student understands that, when DNA is transcribed, the mrna is synthesized in the 5' 3' direction so that it runs antiparallel to the DNA template. (C) The DNA strand is being transcribed from left to right in the 3' should be transcribed in the 5' 3' direction. 5' direction whereas it This answer suggests the student may understand that DNA is only transcribed in one direction, but does not understand that this is always in the 3' 5' direction, and that the mrna is synthesized in the 5' 3' direction, because RNA polymerase can only function moving along the template 3' 5'. In transcription, the result is an mrna polymer. (D) The DNA strand should be arranged in triplets of three bases, and the mrna bases should be arranged into codons. Page 1 of 7

2 This answer suggests the student may understand that information in DNA is arranged in triplets and in codons on mrna, but does not understand that this is not visible on the strands because the DNA and RNA are arranged as continuous sequences of nucleotides, not sets of triplets, and that the error in the diagram is that mrna should be synthesized in the 5' 3' direction, not in the 3' 5' direction. 2. A bacterial gene has just been activated by a regulatory protein, and RNA polymerase binds to the template strand and begins transcription. Which pair of DNA and mrna shows the most accurate representation of the sequences and the resulting transcription of the DNA in the bacterial cell? (A) This answer suggests the student may understand that thymine (T) is not found in RNA, but does not understand that uracil (U) is not present in DNA because DNA uses thymine (T) instead of uracil (U). (B) This answer suggests the student may understand that adenine (A) on DNA pairs with uracil (U) on RNA, but does not understand that thymine (T) on DNA pairs with adenine (A) on RNA. Page 2 of 7

3 (C) This answer suggests the student understands that when DNA is transcribed, the mrna pairs uracil (U) with adenine (A) instead of with thymine (T). (D) This answer suggests the student may understand the base-pairing rules of DNA, but does not understand that when DNA is transcribed, the mrna pairs uracil (U) with adenine (A) instead of with thymine (T), and that uracil (U) is not present in DNA because DNA uses thymine (T) instead of uracil (U). 3. A segment of DNA from a human gene is shown in the diagram below. It is discovered that the same DNA sequence found in another individual carries a mutation. Which choice accurately shows an RNA transcript from the other individual with an explanation of the DNA mutation that resulted in the RNA transcript? Page 3 of 7

4 (A) The resulting RNA transcript is due to a two-base deletion in the DNA sequence. This answer suggests the student understands that a deletion of the third base and fourth base in the DNA sequence results in a shift in the DNA sequence so that ATGCCC becomes ATCC and the resulting RNA sequence becomes UAGG... (B) The resulting RNA transcript is due to a single substitution in the DNA sequence. This answer suggests the student may understand that a substitution in the DNA sequence will result in a change in the resulting RNA sequence, but does not understand that the given RNA transcript is the result of more than one substitution because more than a single base is affected: the RNA transcript for the normal DNA sequence would be UAC GGG AAC CAG UUG, and the given RNA transcript shows two substitutions, one in the third base (G instead of C) and one in the seventh base (U instead of A). (C) The resulting RNA transcript is due to three substitutions in the DNA sequence. This answer suggests the student may understand that substitutions in the DNA sequence will result in a change in the resulting RNA sequence, but does not understand that the given RNA transcript is the RNA transcript for the normal DNA sequence and shows no evidence of substitutions in the normal DNA sequence. (D) The resulting RNA transcript is due to a three-base addition in the DNA sequence. Page 4 of 7

5 This answer suggests the student may understand that an addition to the DNA sequence will result in a change in the resulting RNA sequence, but does not understand that the given RNA transcript is the result of a three-base deletion instead of a three-base addition: the RNA transcript for the normal DNA sequence would be UAC GGG AAC CAG UUG, and the given RNA transcript shows that the third through fifth bases (CCC) were deleted. 4. The table below shows how mrna codons are translated into amino acids. A base substitution in which a guanine (G) base is replaced with a cytosine (C) base occurs on the DNA template shown below. Page 5 of 7

6 Which statement best predicts what will happen to the polypeptide that is translated from this altered DNA template? (A) The substitution will result in no change in the polypeptide, because only the third base in the affected codon will be changed, and only the first two bases in a codon determine the amino acid that is translated. This answer suggests the student may understand that the third base is not as influential as the first and second bases in determining the translated amino acid in many mrna codons, but does not understand that this substitution will cause a significant change in the given polypeptide sequence because this substitution changes the original codon to a stop codon. (B) The substitution will result in a change in the second amino acid to Ile, because the codon will be changed to AUC, which codes for the amino acid Ile. This answer suggests the student may understand that the amino acid translated from the affected codon will change as a result of the base substitution, but does not understand that the polypeptide will stop because the anticodon that pairs with the codon UAG is a stop codon. (C) The substitution will result in only one amino acid being translated, because the second codon will be changed to a stop codon, and translation will immediately stop. This answer suggests the student understands that this base substitution would result in the transcription of the codon UAG, which is a stop codon and would stop polypeptide synthesis. Page 6 of 7

7 (D) The substitution will result in a change in all of the amino acids after the substitution, because the new base will also change the codons translated after the substitution. This answer suggests the student may understand that the base substitution changes the affected codon, but does not understand that although translation of all of the codons downstream of the substitution is stopped prematurely, the actual codons will remain unchanged. Page 7 of 7