The synthesis of DNA is discontinuous on one strand of the replication fork because:

Options

A. DNA molecule being synthesised is very long
B. DNA-dependent DNA polymerase catalyse polymerisation only in one direction (5' `to` 3’)
C. It is more efficient process
D. It help to use DNA ligase

Answer

To answer the question regarding why the synthesis of DNA is discontinuous on one strand of the replication fork, we can break down the explanation into clear steps:

### Step-by-Step Solution:

1. **Understanding DNA Replication**:
- DNA replication occurs at the replication fork, where the double helix unwinds, allowing each strand to serve as a template for the synthesis of a new complementary strand.

2. **Direction of Synthesis**:
- DNA polymerase, the enzyme responsible for synthesizing new DNA, can only add nucleotides in the 5' to 3' direction. This means that it requires a template strand that runs in the opposite direction (3' to 5').

3. **Leading and Lagging Strands**:
- As the replication fork opens, one strand (the leading strand) can be synthesized continuously in the direction of the fork movement. The other strand (the lagging strand) must be synthesized in short segments, known as Okazaki fragments, because it runs in the opposite direction to the fork's movement.

4. **Discontinuous Synthesis**:
- The discontinuous nature of the lagging strand synthesis is due to the need to synthesize in the 5' to 3' direction. As the replication fork progresses, new sections of the lagging strand are synthesized as separate fragments, which are later joined together by the enzyme DNA ligase.

5. **Conclusion**:
- Therefore, the synthesis of DNA is discontinuous on one strand (the lagging strand) because of the antiparallel nature of DNA strands and the requirement of DNA polymerase to synthesize in the 5' to 3' direction.

### Final Answer:
The synthesis of DNA is discontinuous on one strand of the replication fork because DNA polymerase can only synthesize DNA in the 5' to 3' direction, leading to the formation of Okazaki fragments on the lagging strand as it synthesizes in short segments.

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