click to view the pictures
Mitosis is a complex process of nuclear division which ensures each of the two daughter cells receiving a complement copy of genetic materials which are identical to the parent cell. In a non-dividing cell, the genetic material is enclosed in the nuclear membrane where the chromosomes are not visible by light microscope. Before partitioning can occur, the nuclear DNA must go through DNA duplication (S-phase) which is accompanied by chromosome replication. The onset of mitosis is indicated by the appearance of stainable chromosomes as thin threads inside the nucleus. Although mitosis is a continuous process, it is conventionally divided to 4 stages: prophase, metaphase, anaphase and telophase.
Prophase: A stage of chromosome condensation and nuclear membrane disaggregation. The duplicated chromosome subunits
(each one called chromotid) join together at the centromeres. At the late prophase, the microtubular spindle begin to radiate from
the centromeres.
Metaphase: The spindle forms and the chromosomes move to the equator of the cell and align to the equatorial plane.
Anaphase: Two sister chromotids separate into 2 independent chromosomes as the centromere divides. Progressive shortening
of the microtubular spindle fibers pulls the chromosomes in opposite directions toward the poles. At the end of the anaphase, the
chromosomes lie in 2 groups near opposite poles of the spindle. Cytokinesis starts at the middle of the equatorial plane, with the
help of a cytoskeletal phragmoplast.
Telophase: During telophase a nuclear membrane forms around each group of chromosomes, and the chromosomes uncoil and
become less distinct and nucleoli are also formed. The new cell plate expanding centrofugally
interphase: After the completion of cytokinesis, the two daughter
cells enter G1 phase of the cell cycle and start another cell division or sometimes cell elongation.
Both microtubules and microfilaments are involved in mitosis, to drive the movement of the chromosomes.
