Question

Define karyokinesis?

Answer 1

Karyokinesis:

1. Karyokinesis is a step during the cell division whereby the nucleus divides itself to form 2 daughter nuclei. It is usually followed by cytokinesis.
2. In such process, DNA condenses and the chromosomal material divides equally into two halves. It can be carried out with or without cytokinesis.
3. Cytokinesis, on the other side, is generally defined as division of the cytoplasm during the M phase of the cell cycle. It is the 2nd step in M phase.
4. This process also cannot occur without karyokinesis.
5. It is generally the final stage of mitosis, whereby cytoplasm & other cell organelles divide between the two daughter cells.

Steps in karyokinesis:

Prophase:

1. Prophase immediately follows the S and G2 phases of the cycle and is marked by condensation of the genetic material to form compact mitotic chromosomes composed of two chromatids attached at the centromere.
2. The completion of the prophase is characterised by the initiation of the assembly of the mitotic spindle, the microtubules and the proteinaceous components of the cytoplasm that help in the process.
3. The nuclear envelope starts disintegrating.

Prometaphase:

1. In the prometaphase, the nuclear envelop disintegrates.
2. Now the microtubules are allowed to extend from the centromere to the chromosome.
3. The microtubules attach to the kinetochores which allow the cell to move the chromosome around.

Metaphase:

1. At this stage, the microtubules start pulling the chromosomes with equal force and the chromosome ends up in the middle of the cell.
2. This region is known as the metaphase plate.

Anaphase:

1. The splitting of the sister chromatids marks the onset of anaphase.
2. These sister chromatids become the chromosome of the daughter nuclei.
3. The chromosomes are then pulled towards the pole by the fibres attached to the kinetochores of each chromosome.
4. The centromere of each chromosome leads at the edge while the arms trail behind it.

Telophase:

1. The chromosomes that cluster at the two poles start coalescing into an undifferentiated mass, as the nuclear envelope starts forming around it.
2. The nucleolus, Golgi bodies and ER complex, which had disappeared after prophase start to reappear.