How is chromosome replication managed during mitosis?

Chromosome replication during mitosis is managed through a process called DNA replication in the S phase of interphase.

In more detail, the process of mitosis is preceded by a phase known as interphase. Interphase is a period of cell growth and preparation for cell division. It is divided into three stages: G1 (first gap), S (synthesis), and G2 (second gap). During the S phase of interphase, the cell's DNA is replicated. This is a crucial step in preparing for mitosis, as it ensures that each new cell will have a complete set of chromosomes.

DNA replication begins at specific points in the DNA molecule called origins of replication. The DNA double helix is unwound by an enzyme called helicase, creating a replication fork. Another enzyme, DNA polymerase, then adds new nucleotides to the exposed strands following the base pairing rules (adenine with thymine, and cytosine with guanine). This results in two identical DNA molecules, each consisting of one original strand and one newly synthesised strand. This method of replication is known as semi-conservative replication.

Once DNA replication is complete, the cell enters the G2 phase, where it continues to grow and prepare for mitosis. The replicated chromosomes condense and become visible under a microscope. Each replicated chromosome consists of two identical sister chromatids, which are held together at a region called the centromere.

During mitosis, the sister chromatids are separated and distributed to the two daughter cells, ensuring that each new cell receives a complete set of chromosomes. This precise and regulated process of chromosome replication and distribution is essential for maintaining genetic stability and preventing mutations.