Cell Cycle

Cell cycle

Biology

The Cell Cycle is a sequence of changes between cell divisions, including

Interphase (non-division) and
M-phase (division). It involves growth, DNA replication, and division.

Interphase

Interphase is the time between cell divisions, where the cell grows, synthesizes DNA, and prepares for M-phase.

The Interphase is divided into three sub-phases: G1, S, and G2

G1 (Gap one) phase: Period of metabolic activity where the cell grows in size, specific enzymes are synthesized, and DNA base units are accumulated for DNA synthesis.
G0 (G-knot) phase: At a point in G1, the cell may enter G0 (G-knot) phase where cell cycle stops for a period of time.
S (Synthesis) phase: Replication of DNA occurs, resulting in duplication of chromatin material.
G2 (Gap two) phase: Pre-mitotic phase where the cell grows in size, cell organelles replicate, and enzymes required for cell division are synthesized.

M-Phase

During mitosis, a parent cell divides into two daughter cells with the same number of chromosomes. The process can be divided into two phases for study purposes:

(a) Nuclear division or Karyokinesis

Karyokinesis can be further divided into four phases: Prophase, Metaphase, Anaphase, and Telophase.

In Prophase, chromatin condenses into visible chromosomes, each consisting of two chromatids attached at the centromere. The nuclear membrane disappears, and spindle fibers form from centrosomes.
In Metaphase, chromosomes line up on the equator of the spindle and attach to separate spindle fibers at the centromere.
In Anaphase, spindle fibers contract, causing the centromere to divide and the chromatids to separate and move toward opposite poles.
In Telophase, chromatids (chromosomes) reach poles and stop moving. The number of chromosomes in daughter cells is the same as in the parent cell. Nuclear membrane is formed around each set of chromosomes resulting in the formation of two daughter nuclei.

(b) Cytoplasmic division or Cytokinesis

After telophase, the cytoplasm of the cell divides through cytokinesis resulting in the formation of two daughter cells. In animal cells, a constriction develops and deepens to divide the cytoplasm in two equal halves while in plant cells a cell plate is formed. This process leads to the formation of two daughter cells that are exact copies of their parent cell.

Significance of mitosis

Mitosis is crucial for the growth and development of organisms as it creates exact copies of cells. Asexual reproduction and vegetative propagation also rely on mitosis, with some exceptions. The creation of new somatic cells, including blood cells, occurs through mitosis. Mitotic division also facilitates the healing of wounds and the repair of damage within the organism.