Biology – Replication and division of nuclei and cells | e-Consult
Replication and division of nuclei and cells (1 questions)
The mitotic cell cycle is a repeating series of events that lead to the division of a parent cell into two daughter cells. It can be broadly divided into two main phases: interphase and the mitotic (M) phase.
Interphase: This is the preparatory phase, representing the majority of the cell cycle. It is further subdivided into G1, S, and G2 phases:
- G1 Phase (Gap 1): The cell grows in size and synthesizes proteins and organelles. It checks for DNA damage and assesses the environment for suitability for division. If conditions are not favourable, the cell may enter a non-dividing state (G0).
- S Phase (Synthesis): This is the crucial phase where DNA replication occurs. Each chromosome is duplicated, resulting in two identical sister chromatids joined at the centromere.
- G2 Phase (Gap 2): Further growth and protein synthesis occur. The cell checks for DNA damage and ensures that DNA replication is complete. It prepares for mitosis by assembling the mitotic spindle.
Mitotic Phase (M Phase): This is the actual division phase and consists of two main stages: mitosis and cytokinesis.
Mitosis: This is the process of nuclear division, resulting in two genetically identical daughter nuclei. It is divided into five distinct stages:
- Prophase: Chromatin condenses into visible chromosomes. The nuclear envelope breaks down. The mitotic spindle begins to form from the centrosomes.
- Prometaphase: The nuclear envelope completely disappears. Spindle microtubules attach to the kinetochores of the chromosomes.
- Metaphase: Chromosomes align along the metaphase plate (the equator of the cell). Each sister chromatid is attached to microtubules from opposite poles.
- Anaphase: Sister chromatids separate and move to opposite poles of the cell, pulled by the spindle microtubules.
- Telophase: Chromosomes arrive at the poles and begin to decondense. The nuclear envelope reforms around each set of chromosomes. The mitotic spindle disappears.
Cytokinesis: This is the division of the cytoplasm, resulting in two separate daughter cells. In animal cells, cytokinesis occurs through the formation of a cleavage furrow. In plant cells, a cell plate forms down the middle of the cell, eventually developing into a new cell wall.