The Cell Cycle: Interphase and the Phases of the Mitotic Phase
Figure 2. The cell cycle, indicating interphase, and the phases of the mitosis. The stages of the cell cycle; G1, S, G2, and M phase. M phase is the portion of the cell cycle where division takes place. M phase is further divided into 6 phases; prophase, prometaphase, metaphase, anaphase, telophase and cytokinesis. The first part of interphase is G1 shown on the left side of the circle in blue, here the cell grows. The next part of interphase, continuing counterclockwise around the circle, is the S phase shown in green. During this phase the cell duplicates its DNA (dark mass inside the cell) and centrosome (yellow centriole and fiber-like microtubles). The last stage in interphase is G2 or Gap 2 shown at the bottom in lime green, during this phase the cell continues to grow more. Continuing counterclockwise and entering mitosis we reach prophase shown in yellow. During prophase the chromatin condenses into chromosomes and the nucleolus disappears. The next phase is prometaphase shown in orange. During prometaphase the nuclear membrane breaks down, the kinetochore microtubules invade nuclear space and attach to kinetochores, and the polar microtubules push against each other moving the centrosomes apart. Continuing around the circle, now on the right hand side and shown in red, we enter metaphase. During metaphase, the chromosomes (which appear as light blue Xs in the cell) line up along the metaphase plate, or imaginary plane. Next comes anaphase, shown in pink. Here the chromosomes break at the centromeres and sister chromatids (looks like half of a X shown in light blue) move to opposite ends of the cell. The final stages of mitosis are telophase and cytokinesis shown at the top of the circle in a pinkish-purple. During these phases, the nuclear membrane reforms, nucleoli reappear, and chromosomes unwind into chromatin. The myosin II and actin filament ring then contract and cleave the cell in two.
