During DNA replication in eukaryotes, synthesis of the lagging strand requires repeated priming by RNA primase. After primer removal by RNase H and Pol delta, the resulting nicks are sealed. Which enzyme is responsible for joining the Okazaki fragments by sealing single-strand nicks in DNA?

• A DNA polymerase alpha
• B DNA topoisomerase I
• C DNA ligase ✓
• D DNA polymerase epsilon

Explanation

DNA ligase seals the phosphodiester backbone by forming a covalent 3'-5' phosphodiester bond between the 3'-OH of one Okazaki fragment and the 5'-phosphate of the adjacent fragment. Eukaryotic DNA ligase I uses ATP as the energy source (prokaryotic ligase uses NAD+). This ligation step is essential to convert the discontinuously synthesized lagging strand into a continuous DNA strand.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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