Anaphase Information
Anaphase, from the ancient Greek ἀνά (up) and φάσις (stage), is the stage of mitosis or meiosis when chromosomes separate in an eukaryotic cell. Each chromatid moves to opposite poles of the cell, the opposite ends of the mitotic spindle, near the microtubule organizing centers. During this stage, anaphase lag could happen.
Anaphase begins abruptly with the regulated triggering of the metaphase-to-anaphase transition and accounts for approximately 1% of the cell cycle's duration. At this point, anaphase begins. This terminate activity by cleaving and inactivating the M-phase cyclin required for the function of M-phase cyclin dependent kinases (M-Cdks). It also cleaves securin, a protein that inhibits the protease known as separase. Separase then cleaves cohesin, a protein responsible for holding sister chromatids together.
During early anaphase (or Anaphase A), the chromatids abruptly separate and move toward the spindle poles. This is achieved by the shortening of spindle microtubules, with forces mainly being exerted at the kinetochores. Anaphase is when the chromatids separate from each other and move to opposite ends of the cell
- When the chromatids are fully separated, late anaphase (or Anaphase B) begins. This involves the polar microtubules elongating and sliding relative to each other to drive the spindle poles to opposite ends of the cell. Anaphase B drives the separation of sister centrosomes to opposite poles through three forces. Kinesin proteins that are attached to polar microtubules push the microtubules past one another. A second force involves the pulling of the microtubules by cortex-associated cytosolic dynein. The third force for chromosome separation involves the lengthening of the polar microtubules at their plus ends.
These two processes were originally distinguished by their different sensitivities to drugs, and they are mechanically distinct.
- Early anaphase (Anaphase A) involves the shortening of kinetochore microtubules by depolymerization at their plus ends. During this process, a sliding collar allows chromatid movement. No motor protein is involved, as ATP depletion does not inhibit early anaphase.
- Late anaphase (Anaphase B) involves both the elongation of overlapping microtubules and the use of two distinct sets of motor proteins: one pulls overlapping microtubules past each other, and the other pulls astral microtubules that have attached to the cell cortex.
The contributions of early anaphase and late anaphase to anaphase as a whole vary by cell type. In mammalian cells, late anaphase follows shortly after early anaphase and extends the spindle to approximately twice its metaphase length; by contrast, yeast and certain protozoans use late metaphase as the main means of chromosome separation and, in the process, can extend their spindles to up to 15 times the metaphase length.
See also
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en:Անաֆազ
Categories: Mitosis
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