Cells which are not dividing are non-cycling or G0 cells. In most tissues only a small proportion of cells are in the cell cycle, the majority being differentiated cells in a G0 phase. Stem cells may be in a G0 phase and only re-enter the cell cycle if needed, for example following cell death.
Cell division. Follow the line from G1 and go counter-clockwise.
G1 phase cells have just entered the phase of cellular growth. In S phase cells actively duplicate DNA, by DNA replication, so that G2 cells have a double complement of DNA and are resting prior to cell division. Finally, M phase comprises of cells in mitosis followed by cytokinesis. This will be now be described in detail: Mitosis, which is divided into 5 different stages, is the process of nuclear division in eukaryotic cells. In which each member of a duplicated chromosome segregates into a daughter nucleus, resulting in daughter nuclei containing identical sets of chromosomes identical to that of the parent nucleus, followed by cytokinesis.
During prophase duplicated interphase chromatin condenses into well-defined chromosomes and the previously duplicated centrosomes migrate apart, thereby defining the poles of the future spindle apparatus. Concomitantly, centrosomes begin nucleating highly dynamic microtubules that probe space in all directions, and the nuclear envelope breaks down.
During prometaphase microtubules are captured by kinetochores (specialized proteinaceous structures associated with centromere DNA on mitotic chromosomes). Although monopolar attachments of chromosomes are unstable, the eventual interactions of paired sister chromatids with microtubules originating from opposite poles result in a stable, bipolar attachment.
Chromosomes assemble to form an equatorial plate, where they continue to oscillate throughout metaphase, suggesting a balance of forces that keeps them under tension.
After all the chromosomes have undergone a proper bipolar attachment, a sudden loss in sister chromatin cohesion triggers the onset of anaphase. Sister chromatids are then pulled towards the poles and the poles themselves separate further towards the cell cortex.
Once the chromosomes have arrived at the poles, nuclear envelopes reform around the daughter chromosomes, and chromatin decondensation begins (telophase). Finally, an actomycin-based contractile ring is formed and cytokinesis is completed.
