Final answer:
DNA Polymerase III possesses a high degree of proficiency in nucleotide selection, with an error rate of about one error per 10 million nucleotides contributed by its proofreading function.
Step-by-step explanation:
The active site of DNA Polymerase III exhibits a high level of nucleotide selection proficiency, making it an essential player in the faithful replication of DNA. Remarkably, DNA Polymerase III's error rate is extremely low, at approximately one error per 10 million nucleotides. This high degree of accuracy is due in large part to the proofreading activity of DNA Polymerase III, which actively corrects incorrect base pairings as part of its exonuclease function.
During the replication process, when DNA Polymerase III adds a nucleotide to the growing DNA strand, it proofreads the newly incorporated base. If the polymerase detects that the wrong nucleotide has been inserted, it triggers an exonuclease activity that cleaves the phosphodiester bond of the incorrect nucleotide. After excising the erroneous base, the polymerase can then insert the correct nucleotide, thus maintaining the integrity of the DNA sequence.
Despite its high fidelity, occasional mistakes that slip through the proofreading process are addressed by additional DNA repair mechanisms in the cell, which further reduce the occurrence of mutations. These multi-layered corrective systems ensure that the DNA replication process remains highly accurate, enabling the stable inheritance of genetic information.