AP BIOLOGY

Detailed explanation-1: -There is substantial biochemical evidence indicating that DNA ligase I, which is one of four DNA ligases in mammalian cells (1, 2), is the enzyme responsible for joining Okazaki fragments.

Detailed explanation-2: -Abstract. DNA ligase 1 (LIG1, Cdc9 in yeast) finalizes eukaryotic nuclear DNA replication by sealing Okazaki fragments using DNA end-joining reactions that strongly discriminate against incorrectly paired DNA substrates.

Detailed explanation-3: -DNA ligase I is responsible for joining Okazaki fragments together to form a continuous lagging strand. Because DNA ligase I is unable to join DNA to RNA, the RNA-DNA primers must be removed from each Okazaki fragment to complete lagging strand DNA synthesis and maintain genomic stability.

Detailed explanation-4: -DNA polymerase I is recognized as an enzyme that fills any remaining gaps between Okazaki fragments and removes RNA primers with a duplex-specific 5′-3′ exonuclease activity, providing a nick that can be sealed by DNA ligase 31, 32.