Which enzyme connects Okazaki fragments on the lagging strand by forming covalent bonds?

• A. DNA ligase
• B. RNA primase
• C. Base pairs
• D. Hydrogen bond

Answer: (A)

Joining the short pieces on the lagging strand requires a covalent bond to stitch the backbone together. After primers are laid and each fragment is extended, the gaps between adjacent Okazaki fragments are joined by DNA ligase, which catalyzes the formation of phosphodiester bonds between the adjacent 3' end of one fragment and the 5' end of the next. This covalent linkage converts a series of fragments into a continuous strand. In contrast, RNA primase just lays down the RNA primers, so it doesn’t seal the fragments. Base pairs and hydrogen bonds are the non-covalent interactions that stabilize the DNA double helix, not the covalent backbone connection between fragments.