DNA replication includes :-

Options

A. DNA ligase
B. DNA polymerase and ligase
C. RNA polymerase and ligase
D. All of these

Answer

**Step-by-Step Solution:**

1. **Understanding DNA Replication**: DNA replication is the process by which a single DNA molecule is copied to produce two identical DNA molecules. This is essential for cell division and ensures that each daughter cell receives an exact copy of the DNA.

2. **Key Enzymes Involved**: The main enzymes involved in DNA replication are:
- **DNA Polymerase**: This enzyme synthesizes new DNA strands by adding nucleotides complementary to the template strand. It works in the 5' to 3' direction.
- **DNA Ligase**: This enzyme is responsible for joining Okazaki fragments on the lagging strand, sealing nicks in the sugar-phosphate backbone of the DNA.

3. **Strands of DNA**: During replication, one strand is referred to as the leading strand, which is synthesized continuously in the 5' to 3' direction. The other strand is called the lagging strand, which is synthesized discontinuously in short segments known as Okazaki fragments.

4. **Formation of Okazaki Fragments**: On the lagging strand, DNA polymerase synthesizes short segments of DNA (Okazaki fragments) because it cannot synthesize in the 3' to 5' direction. These fragments are later joined together by DNA ligase to form a continuous strand.

5. **Conclusion**: The question asks what DNA replication includes. Based on the roles of the enzymes discussed, the correct answer is that DNA replication includes **DNA polymerase and DNA ligase**.

**Final Answer**: DNA replication includes DNA polymerase and DNA ligase.

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