DNA copying or replication occurs during cell division. DNA replication takes place during the ‘S’ phase (synthesis phase) of the cell cycle. ‘S’ phase is followed by ‘M’ phase or mitosis phase, where chromosomes segregate.
In the ‘S’ phase, DNA content of chromosomes gets duplicated and it is an important step, so that daughter cells contain the same amount of DNA as the parent cell. Cell division is required for growth differentiation and gamete formation. Interphase is divided into three stages G1, S and G2. DNA copying takes place in the S phase of the interphase nucleus.
Also see: 4 Phases of Cell Cycle
DNA copying is better known as DNA replication. It is an essential step for the continuity of genome during cell proliferation, repair and gamete formation.
DNA replication is semiconservative, i.e. one of the parent strands is conserved and the other strand of double-stranded DNA is newly formed. In eukaryotes DNA replication is discontinuous. DNA polymerase catalyses the reaction in 5’→3’ direction.
Replication starts at the origin of replication and unwinding of DNA double strands takes place forming a replication fork. The enzyme DNA helicase catalyses the unwinding process. The leading strand is replicated continuously and the lagging strand is replicated discontinuously forming Okazaki fragments, which are joined by another enzyme known as DNA Ligase.
Explore more: 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 DNA content is doubled. DNA duplication takes place in the nucleus. Centriole also duplicates during the ‘S’ phase but in the cytoplasm.
This was in brief about the DNA replication during cell division. Get access to all the NEET Questions with explanations, only at BYJU’S.