Final answer:
The 3' → 5' exonuclease activity is crucial for DNA polymerase I's proofreading function, ensuring high-fidelity DNA replication by removing and replacing mismatched nucleotides.
Step-by-step explanation:
The Role of 3' → 5' Exonuclease Activity in DNA Replication
The 3' → 5' exonuclease activity is critical for the proofreading function during DNA replication, predominantly carried out by DNA polymerase I. This activity ensures that any incorrectly paired nucleotides are recognized and removed, maintaining the fidelity of replication. DNA polymerase I adds nucleotides in a 5'-3' direction, but it also scans and removes mismatched nucleotides in the opposite direction (3'-5') through its exonuclease activity. Should this proofreading mechanism be nonfunctional, it would result in an increased number of mutations, as incorrect bases would not be removed and subsequently replaced with accurate pairs.
Moreover, this activity also plays a role in DNA repair and the removal of RNA primers in Okazaki fragments on the lagging strand, which are essential processes in preserving the integrity of the genetic material. Without a properly functioning exonuclease activity, DNA polymerase I would lack the capability to correct errors, leading to a higher mutation rate and potential malfunctions in cellular processes dictated by the affected DNA.