The nuclear envelope completely disintegrates at the onset of metaphase and the condensed chromosomes spread throughout the cytoplasm. These chromosomes are composed of two sister chromatids held at the center by centromeres. The spindle fibers attach to a disc-like structure at the surface of centromeres, known as kinetochores. The spindle fibers from one centriole attach to only one sister chromatid. The chromosomes aligned along the equator of the cytoplasm, an arrangement characteristic of metaphase known as metaphase plate.