In DNA replication, which mechanism primarily helps prevent errors by removing misincorporated nucleotides during DNA synthesis?

• A. 3′→5′ exonuclease proofreading activity of DNA polymerase
• B. 5′→3′ exonuclease activity that removes RNA primers
• C. Photoreactivation by DNA photolyase to reverse thymine dimers
• D. Nucleotide excision repair that removes bulky lesions after replication

Answer: (A)

Verified step by step guidance

1. Understand that DNA replication involves synthesizing a new strand complementary to the template strand, and accuracy is crucial to prevent mutations.
2. Recognize that DNA polymerase has intrinsic activities that contribute to replication fidelity, including the ability to add nucleotides and to correct errors.
3. Identify that the 3′→5′ exonuclease activity of DNA polymerase acts as a proofreading mechanism by removing incorrectly paired nucleotides immediately after they are added.
4. Distinguish this proofreading activity from other mechanisms such as 5′→3′ exonuclease activity, which primarily removes RNA primers, and repair systems like photoreactivation or nucleotide excision repair that act after replication or on different types of damage.
5. Conclude that the primary mechanism preventing errors during DNA synthesis by removing misincorporated nucleotides is the 3′→5′ exonuclease proofreading activity of DNA polymerase.