Replication and division of nuclei and cells

Replication and Division of Nuclei and Cells

The Cell Cycle

  • The cell cycle is a series of events in the life of a cell from when it is first formed from a dividing parent cell until its own division into two new cells.
  • All cells go through a growth and division cycle known as interphase and mitotic phase.
  • Interphase is composed of three stages: the G1 phase (cell growth), the S phase (DNA replication), and the G2 phase (preparation for mitosis).
  • Mitosis, on the other hand, involves the division of the nucleus and is followed by cytokinesis, the division of cytoplasm.

DNA Replication in the S Phase

  • Each DNA molecule is semi-conservatively replicated during the S phase of the cell cycle. This process ensures the two daughter cells receive identical copies of the genetic material.
  • The DNA double helix unwinds and an enzyme called DNA polymerase adds new nucleotides to each strand, thereby producing two identical DNA molecules.

Mitosis and Cytokinesis

  • The mitotic phase tallies for about 10% of the cell cycle and it is divided into five stages, namely, prophase, prometaphase, metaphase, anaphase, and telophase.
  • During prophase, the nuclear membrane starts to disappear while the chromosomes start to condense.
  • In prometaphase, the nuclear membrane disappears completely. The chromosomes are now clearly visible, and spindle fibres attach to the centromeres of the chromosomes.
  • Metaphase time leads to the chromosomes lining up at the metaphase plate, in the middle of the cell.
  • In anaphase, the centromeres split, and the chromatids are pulled apart to opposite poles of the cell.
  • At telophase, a new nuclear envelope forms around the chromosomes at each end of the cell.
  • The process of cytokinesis splits the cytoplasm, resulting in two new cells.

Regulation of Cell Cycle

  • The cell cycle is tightly regulated by checkpoints to avoid errors that can lead to cancer and other diseases.
  • These checkpoints in the cell cycle are in place to ensure that each phase is completed correctly and the DNA has been correctly replicated and divided.
  • If a problem is detected, the cell cycle is halted until the error can be corrected.