ACTIVITY 2A: CELL DIVISION - MITOSIS

• Cell division is an important process in living organisms.

  • It is involved in the multiplication of cells for growth and development of an organism.
  • It plays a key role in repairing injured body parts of animals.
• Cell division can be viewed as a cycle, which can be arbitrarily, categorized into two stages namely interphase and mitosis.
• Interphase

  • wherein the cell undergoes growth and prepares for cell division, might comprise as much as 90% of the cycle.
  • All the necessary materials needed for cell divisions, which include microtubule proteins among others, are synthesized at this stage.
  • To ensure that each daughter cell would have a complete set of genetic material, actual replication of genetic material of DNA occurs in this phase.
• Once the preparatory stages are completed the cell undergoes the actual cell division or mitosis. Although, mitosis comprises 10% of the cycle, cell biologists consider several phases in mitosis based on the different events occurring in the nucleus and cytoplasm of the cell.
• Interphase:

  • With a distinct nucleus that is with an intact nuclear membrane
  • The genetic materials inside the nucleus appear as thin, thread-like structures which are called chromatin.
  • Within the nucleus is 1-2 nucleoli which are dense, darkly stained bodied formed by several chromosomal materials
• M-phase:

  • phase where the cell divides
  • divided into 4 stages
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Prophase:

  • Where the nuclear membrane starts to disintegrate or disappear
  • The chromatin fibers start to appear as coiled, thickened, condensed structure forming chromosomes that are visible under the light microscope
• Metaphase:

  • The chromosomes are aligned at the equatorial region of the nucleus
  • The replicated chromosomes are much shorter, and more condensed, and are readily recognized
  • The chromosomes are made up of chromatids joined together at their central region called centromere.
  • A protein coat called kinetochore is found in each of the sister chromatid. The spindle fibers are attached at the centromere of each chromosome.
• Anaphase:

  • where the chromatids are pulled apart toward the opposite poles. This stage is differentiated into early and late stages depending on the distance travelled by the chromatids.
  • Once the chromatids separate, these are considered as chromosomes reaching the opposite poles.
• Telophase:

  • where a cleavage furrow, a constriction of the plasma membrane at the region of the equatorial plate starts to appear. This is the start of early telophase.
  • At this stage the nuclear membrane and the nucleolus start to reappear. The chromosomes begin to uncoil and assume a threadlike appearance. The asters and mitotic spindles disappear.
  • At the late stage of this phase, the cleavage furrow becomes more constricted leading to the formation of 2 daughter cells.
• Cytokinesis:

  • which is the division of the cytoplasm usually, occurs along with telophase.
  • Completely separated daughter cells are formed soon after mitosis.