Arrange the following steps in correct order:
(DNA replication):
(I) Topoisomerase stabilises the helix in phases.
(II) Okazaki fragments are formed during DNA replication.
(III) Helicase unwinds the helix in phases.
(IV) Ligase joins the Okazaki segments

Options

A. (I), (II), (III), (IV)
B. (IV), (III), (II), (I)
C. (III), (I), (II), (IV)
D. (II), (III), (IV), (I)

Explanation

To arrange the steps of DNA replication in the correct order, we need to understand the role of each enzyme and the sequence of events that occurs during the replication process. Here’s the step-by-step solution:

### Step-by-Step Solution:

1. **Topoisomerase Stabilizes the Helix**:
- Before the DNA can be unwound, the topoisomerase enzyme works to stabilize the DNA helix. It prevents the DNA from becoming too tightly coiled and allows for the unwinding process to occur smoothly.

2. **Helicase Unwinds the Helix**:
- Once the topoisomerase has stabilized the DNA, the helicase enzyme unwinds the double-stranded DNA. This unwinding occurs in phases, creating a replication fork where the two strands of DNA are separated.

3. **Okazaki Fragments are Formed**:
- As the helicase unwinds the DNA, the leading strand is synthesized continuously, while the lagging strand is synthesized in short segments known as Okazaki fragments. This occurs because DNA synthesis can only proceed in the 5' to 3' direction.

4. **Ligase Joins the Okazaki Segments**:
- Finally, the DNA ligase enzyme comes into play. It connects the Okazaki fragments on the lagging strand, sealing the gaps and forming a continuous DNA strand.

### Correct Order of Steps:
1. (I) Topoisomerase stabilizes the helix.
2. (III) Helicase unwinds the helix in phases.
3. (II) Okazaki fragments are formed during DNA replication.
4. (IV) Ligase joins the Okazaki segments.