Which of the following nucleic acid complexes would undergo correction by the DNA mismatch repair system?

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11ecba2d_0fd2_7ccd_a3bf_21cf450829ce_MD0008_00 During DNA replication, DNA polymerase may mistakenly incorporate an incorrect nucleotide into the newly synthesized strand, creating a base pair mismatch between the daughter and the parent strands (ie, G-T and A-C mispairing instead of the proper G-C and A-T pairing). The presence of the mismatched base activates the DNA mismatch repair (MMR) machinery, in which a nuclease enzyme excises the erroneous nucleotide, as well as several nucleotides flanking either side of the incorrectly matched base, from the daughter strand. DNA polymerase then incorporates the appropriate nucleotides, and DNA ligase catalyzes the formation of new phosphodiester bonds to seal the gap between the strands. In this scenario, the correct DNA sequence would need to contain a pair of mismatched bases. The DNA complex in Choice C has a mismatch at the twelfth base pair that, once corrected, would produce an accurate complementary DNA strand. (Choices A and D) The MMR machinery corrects only replication errors within DNA strands. These complexes depict transcription, the production of an RNA transcript from a DNA template. The mRNA synthesized from the DNA template can be identified by the presence of A-U instead of A-T base pairs. The complex in Choice A shows a normal (error-free) mRNA strand transcribed from a DNA strand. In contrast, the complex in Choice D shows that RNA polymerase made an error during transcription at the fifth base of the mRNA strand (ie, C should be U). Regardless, the MMR would not be activated for either complex because it is not involved in mRNA synthesis or repair of transcription errors. (Choice B) There is no mismatched base in these DNA strands; therefore, the MMR machinery would not be activated. Educational objective: Base pair mismatches occur when DNA polymerase incorporates an incorrect nucleotide into the newly synthesized strand. DNA mismatch repair is the process by which base pair mismatches between the daughter and the parent strands are corrected during DNA replication.

Which of the Following Nucleic Acid Complexes Would Undergo Correction