Mitosis - Prophase
Description:
Prophase is the longest phase among all the phases of karyokinesis. It is studied in three sub phases: early, mid and late prophase.
Changes that a cell undergoes during the following phases are −
Early Prophase
Nucleus becomes spheroidal.
Condensation of interwoven DNA molecules to form elongated chromosomes.
Shortening and thickening of chromosome fibres is possible due to two reasons −
- Coming together of scaffolding or axial proteins.
- Coiling of chromatin fibres.
Condensins are the proteins which assist the coiling of chromosomes.
In the beginning of the prophase, animal cells have two centrosomes or centriole pairs close together.
Centrioles begin to shift towards the opposite sides.
Each centriole pair develops fine, radiating protein-microtubules called astral rays forming star shaped body called aster.
Mid Prophase
Further condensation of chromosomes so that they become shorter, thicker and entangled.
Due to elongation of the microtubules the two asters separate further.
Nuclear membrane and nucleolus start disappearing.
Late Prophase
Complete disappearance of golgi body, ER, nuclear membrane and nucleolus.
More condensation of chromosomes.
Chromosomes move towards a nuclear membrane and leaves a clear central area.
Two asters become antipodal in position and the proteinous microtubules between them take the form of spindle.
Asters and spindle are collectively called mitotic apparatus.