## **Core Concept**
Okazaki fragments are short, discontinuous segments of DNA synthesized in the lagging strand during DNA replication. The process of joining these fragments into a continuous strand is crucial for the completion of DNA replication. This process involves specific enzymes that facilitate the formation of a continuous DNA strand.

## **Why the Correct Answer is Right**
The correct answer, **DNA Ligase**, is the enzyme responsible for joining Okazaki fragments on the lagging strand. DNA Ligase forms a phosphodiester bond between the 5' end of one Okazaki fragment and the 3' end of another, effectively sealing the gaps between the fragments. This action requires energy, which is often provided by ATP or NAD+. DNA Ligase is essential for creating a continuous strand of DNA from the discontinuous Okazaki fragments.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While helicases are crucial for unwinding double-stranded DNA into single strands during replication, they are not involved in joining Okazaki fragments.
- **Option B:** Polymerases are responsible for synthesizing new DNA strands by adding nucleotides to the template strand. While they initiate the synthesis of Okazaki fragments, they do not join these fragments together.
- **Option D:** Topoisomerases are involved in relieving supercoils that form ahead of the replication fork and are not directly involved in the joining of Okazaki fragments.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that DNA Ligase is essential for DNA replication and repair. Inhibitors of DNA Ligase can act as anticancer agents by preventing cancer cells from replicating their DNA. A classic example is the use of drugs that target DNA Ligase in the treatment of certain malignancies.

## **Correct Answer:** . DNA Ligase