The overall error rate in the completed DNA molecule after replication and repair is approximately __________.

• A. 1 error per 10^3 nucleotides
• B. 1 error per 10^6 nucleotides
• C. 1 error per 10^9 nucleotides
• D. 1 error per 10^12 nucleotides

Answer: (C)

Verified step by step guidance

1. Understand that DNA replication involves multiple steps that contribute to the overall fidelity, including the base-pairing accuracy of DNA polymerase, the proofreading activity of DNA polymerase, and the post-replication mismatch repair system.
2. Recognize that the initial error rate of DNA polymerase without proofreading is about 1 error per 10^5 nucleotides incorporated due to incorrect base pairing.
3. Consider that the proofreading function of DNA polymerase reduces this error rate by about 100-fold, improving accuracy to approximately 1 error per 10^7 nucleotides.
4. Acknowledge that the mismatch repair system further corrects errors missed by proofreading, enhancing fidelity by another 100- to 1000-fold, leading to a final error rate around 1 error per 10^9 nucleotides.
5. Combine these sequential error-correcting steps conceptually to understand why the overall error rate after replication and repair is approximately 1 error per 10^9 nucleotides.