The S period is where the synthesis of both the DNA and histones. The third stage is called the G2 stage. In this last stage of interphase the division of the mitochondria and other organelles. The G1 phase undergoes the formation of structure and substances, such as the microtubules which are directly involved in mitosis. In prophase, the chromosomes become shorter and thicker, and the nuclear envelope and nucleolus disappear.
Prophase takes as much time as the other three phases combined.
This stage can be depicted by the appearance of the chromosomes that look like swelling threads within the nucleus. The swelled chromosomes will eventually form two strands of chromatids. The chromatids are held together by a dense constricted portion called centromere. A dense protein disk called kinetochore , located near the centromere the spindle fibers attach. As prophase progresses the nucleolus appears to fade and eventually disappears.