1. Interphase:
* G1 Phase (First Gap): The cell grows and synthesizes proteins, organelles, and other cellular components needed for DNA replication.
* S Phase (Synthesis): The cell replicates its DNA, resulting in two identical copies of each chromosome.
* G2 Phase (Second Gap): The cell continues to grow and prepares for mitosis by synthesizing proteins involved in cell division and checking for DNA replication errors.
2. Prophase:
* Chromatin Condensation: The replicated DNA condenses into visible chromosomes, each consisting of two identical sister chromatids joined at the centromere.
* Nuclear Envelope Breakdown: The membrane surrounding the nucleus disintegrates, allowing the chromosomes to access the cytoplasm.
* Spindle Formation: Microtubules begin to assemble, forming the mitotic spindle, which will guide the separation of chromosomes.
* Centriole Movement: In animal cells, centrioles migrate to opposite poles of the cell, forming the poles of the mitotic spindle.
3. Metaphase:
* Chromosomes Align: The chromosomes line up along the equator of the cell, forming the metaphase plate.
* Spindle Attachment: Microtubules from the spindle attach to the kinetochores, specialized protein structures at the centromere of each chromosome.
4. Anaphase:
* Sister Chromatid Separation: The centromeres of each chromosome separate, and the sister chromatids are pulled apart by the shortening microtubules.
* Chromosome Movement: The separated chromatids (now individual chromosomes) move to opposite poles of the cell.
5. Telophase:
* Chromatin Decondensation: The chromosomes reach the poles and begin to uncoil, becoming less condensed.
* Nuclear Envelope Reformation: New nuclear membranes form around the chromosomes at each pole, creating two separate nuclei.
* Cytokinesis (Cell Division): The cytoplasm divides, forming a cleavage furrow (in animal cells) that pinches inward, eventually separating the two daughter cells.
Key Points:
* Mitosis ensures the accurate duplication and distribution of chromosomes to daughter cells, maintaining the genetic integrity of the organism.
* Animal cells divide by cytokinesis, which involves the formation of a cleavage furrow that constricts the plasma membrane.
* The spindle apparatus, consisting of microtubules, plays a critical role in chromosome movement during mitosis.
* Cell cycle checkpoints regulate the progression of cell division, ensuring proper DNA replication and preventing uncontrolled cell growth.
In summary, cell division in animal cells is a complex process that involves the coordinated action of numerous cellular components. It ensures the accurate duplication and distribution of genetic material, allowing for growth, development, and tissue repair.
