Table of Contents
What Is Anaphase?
Anaphase is the third phase of mitosis after prophase and metaphase, where the chromosomes are replicated and split apart into daughter chromosomes located at the opposite ends of the cell. At this stage, the chromosomes are at the maximum level of condensation; this helps in easy segregation and formation of the nucleus.
Activity during Anaphase
At the time of anaphase, the anaphase-promoting complex marks the destruction of securin by ubiquitination. Securin is an inhibitory chaperone that inhibits another protease called separase. After the destruction of securin, separase is released in the cells, which breaks down another protein called cohesin that holds sister chromatids together.
Three classes of microtubules – interpolar microtubules, kinetochore microtubules and astral microtubules – create forces that are necessary for the separation of sister chromatids. As a result, the centromere is split, and the daughter chromatids are pulled towards opposite poles by the kinetochore microtubules. They produce an intermediary Y-shape or V-shape while being pulled to the opposite ends.
The other microtubules create forces that stretch the cell into an oval shape, while the chromatids are at opposite poles. After this, the cells enter the telophase stage.
Refer: The Second Stage of Mitosis – Metaphase
Phases
Anaphase can be distinguished into two phases:
Anaphase A
Anaphase A is characterised by the movement of chromosomes to the opposite poles with the help of kinetochore microtubules. The microtubules create a central force by attaching themselves to the centromere of the chromosomes. The attached microtubule depolymerises and becomes shorter and pulls the chromosomes apart towards the centrosomes, along with the help of motor proteins.
Anaphase B
Anaphase B is characterised by the separation of poles from each other with the assistance of astral and interpolar microtubules. The interpolar microtubules arise from the centrosome; they push against each other to throw the centrosomes further away.
Similarly, the astral microtubules arise from the centrosome and join at the cell membrane. They create forces to pull centrosomes close to each other. The expanding and shrinking movements created by the microtubules, along with motor proteins dyneins and kinesins, bring together the process of chromosome separation.
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