Multiple Choice
Which of the following pathways is an error-free way to repair double-stranded breaks?
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17. Mutation, Repair, and Recombination
DNA Repair
2:19 minutesProblem 13f
Textbook Question
Answer the following questions concerning the accuracy of DNA polymerase during replication.
DNA mismatch repair can accurately distinguish between the template strand and the newly replicated strand of a DNA duplex. What characteristic of DNA strands is used to make this distinction?
Verified step by step guidance1
Understand the role of DNA mismatch repair: DNA mismatch repair is a system that corrects errors introduced during DNA replication, such as mismatched base pairs.
Recognize the key characteristic used for strand distinction: DNA mismatch repair relies on the fact that the newly synthesized strand is not yet fully modified compared to the template strand.
Explain the specific modification: In prokaryotes, the template strand is methylated at specific sites (e.g., adenine residues in GATC sequences), while the newly synthesized strand is temporarily unmethylated.
Describe how this distinction is utilized: The mismatch repair machinery identifies the unmethylated strand as the newly synthesized strand and corrects errors on this strand to match the template strand.
Highlight the importance of timing: The methylation of the newly synthesized strand occurs after a short delay, allowing the repair system to distinguish between the strands during replication.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
DNA Mismatch Repair
DNA mismatch repair is a cellular mechanism that corrects errors that occur during DNA replication. It identifies and repairs mismatched base pairs, ensuring the fidelity of DNA synthesis. This process is crucial for maintaining genetic stability and preventing mutations that could lead to diseases, including cancer.
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Repair Pathways
Template Strand vs. Newly Synthesized Strand
During DNA replication, the original DNA strand is referred to as the template strand, while the newly synthesized strand is created based on this template. The distinction between these two strands is essential for mismatch repair, as the repair machinery must recognize which strand contains the correct sequence and which contains the error.
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DNA Strand Methylation
One key characteristic used to distinguish between the template and newly synthesized strands is DNA strand methylation. In many organisms, the template strand is often methylated, while the newly synthesized strand is not immediately methylated. This difference allows the mismatch repair system to identify and correct errors by targeting the unmethylated strand.
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