Prophase, from the ancient Greek πρό (before) and φάσις (stage), is a stage of mitosis in which the chromatin condenses (it becomes shorter and fatter) into double rod-shaped structures called chromosomes in which the chromatin becomes visible. This process, called chromatin condensation, is mediated by the condensin complex. Since the genetic material has been duplicated in an earlier phase of the cell cycle, there are two identical copies of each chromosome in the cell, call homologous chromosomes. Identical chromosomes, called sister chromatids, are attached to each other at a DNA element present on every chromosome called the centromere. Also during prophase, giemsa staining can be applied to elicit G-banding in chromosomes. Also, once the chromosomes form, the nucleolus fades. Prophase accounts for approximately 3% of the cell cycle's duration.
An important organelle in mitosis is the centrosome, the microtubule organizing center in metazoans. During prophase, the two centrosomes, which replicate independently of mitosis, have their microtubule-activity increased due to the recruitment of γ-tubulin. The centrosomes will be pushed apart to opposite ends of the cell nucleus by the action of molecular motors acting on the microtubules.
Basically, the chromatin in the nucleus coils into chromosomes. The nucleolus disintegrates and the centrosomes move to opposite poles of the cell, forming a bridge of spindle fibers.
Prometaphase, the next step of mitosis, will see the nuclear membrane fall apart and the chromosomes being captured by the microtubules.
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