When Does Dna Copying Occur

During the S phase (synthesis phase) of the cell cycle, DNA copying or replication occurs. After S phase is complete, M phase (mitosis phase) begins and chromosomes segregate.

In the S phase, the DNA content of chromosomes is duplicated, which is an important step in order for the daughter cells to contain the same amount of DNA as the parent cell. Cell division is essential for growth, differentiation, and gamete formation. Interphase is divided into three stages: G1, S, and G2. DNA replication occurs during the S phase of the interphase nucleus.

![Cell Cycle]()

4 Phases of Cell Cycle, check it out!

DNA Replication

DNA replication is better known as the copying of DNA. It is an essential step for the continuity of the genome during cell proliferation, repair, and gamete formation.

DNA replication is semiconservative, i.e. one of the parent strands is conserved while the other strand of double-stranded DNA is newly formed. In eukaryotes, DNA replication is discontinuous. DNA polymerase catalyses the reaction in the 5’→3’ direction.

DNA Replication

DNA helicase catalyses the unwinding of DNA double strands at the origin of replication, forming a replication fork. The leading strand is then replicated continuously, while the lagging strand is replicated discontinuously forming Okazaki fragments. These fragments are then joined together by another enzyme known as DNA Ligase.

Learn more about the Molecular Basis of Inheritance

It is important to note that the chromosome number of the cell remains the same during the S phase and only the DNA content is doubled. DNA duplication takes place in the nucleus. Centriole also duplicates during the S phase but in the cytoplasm.

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