Phases of the cell cycle (article) | Khan Academy
M phase. A nuclear division (mitosis) followed by a cell division (cytokinesis). Chromosomes replicated during the S phase are divided in such a way as to. The cell cycle is composed of interphase (G₁, S, and G₂ phases), followed by the mitotic phase (mitosis and cytokinesis), and G₀ phase. One “turn” or cycle of the cell cycle consists of two general phases: interphase, followed by mitosis and cytokinesis. Interphase is the period of the cell cycle.
Prometaphase The chromosomes, led by their centromeres, migrate to the equatorial plane in the mid-line of the cell - at right-angles to the axis formed by the centrosomes.Mitosis and Cytokinesis
This region of the mitotic spindle is known as the metaphase plate. The spindle fibres bind to a structure associated with the centromere of each chromosome called a kinetochore. Individual spindle fibres bind to a kinetochore structure on each side of the centromere. The chromosomes continue to condense. Metaphase The chromosomes align themselves along the metaphase plate of the spindle apparatus.
Anaphase The shortest stage of mitosis. The centromeres divide, and the sister chromatids of each chromosome are pulled apart - or 'disjoin' - and move to the opposite ends of the cell, pulled by spindle fibres attached to the kinetochore regions. The separated sister chromatids are now referred to as daughter chromosomes.
It is the alignment and separation in metaphase and anaphase that is important in ensuring that each daughter cell receives a copy of every chromosome. Telophase The final stage of mitosis, and a reversal of many of the processes observed during prophase.
Animal Cell Mitosis
The nuclear membrane reforms around the chromosomes grouped at either pole of the cell, the chromosomes uncoil and become diffuse, and the spindle fibres disappear. Cytokinesis The final cellular division to form two new cells.
In plants a cell plate forms along the line of the metaphase plate; in animals there is a constriction of the cytoplasm. The cell then enters interphase - the interval between mitotic divisions. Meiosis Meiosis is the form of eukaryotic cell division that produces haploid sex cells or gametes which contain a single copy of each chromosome from diploid cells which contain two copies of each chromosome.
As in mitosis, meiosis is preceded by a process of DNA replication that converts each chromosome into two sister chromatids.
Meiosis I Meiosis I separates the pairs of homologous chromosomes. Related cell processes[ edit ] Cell rounding[ edit ] Cell shape changes through mitosis for a typical animal cell cultured on a flat surface. The cell undergoes mitotic cell rounding during spindle assembly and then divides via cytokinesis. Rounding also occurs in live tissue, as described in the text. Mitotic cell rounding In animal tissue, most cells round up to a near-spherical shape during mitosis.
Generation of pressure is dependent on formin -mediated F-actin nucleation  and Rho kinase ROCK -mediated myosin II contraction,    both of which are governed upstream by signaling pathways RhoA and ECT2   through the activity of Cdk1. Mitotic recombination[ edit ] Mitotic cells irradiated with X-rays in the G1 phase of the cell cycle repair recombinogenic DNA damages primarily by recombination between homologous chromosomes.
Evolution[ edit ] Some types of cell division in prokaryotes and eukaryotes There are prokaryotic homologs of all the key molecules of eukaryotic mitosis e. Being a universal eukaryotic property, mitosis probably arose at the base of the eukaryotic tree. As mitosis is less complex than meiosismeiosis presumably arose after mitosis. In relation to the forms of mitosis, closed intranuclear pleuromitosis seems to be the most primitive type, as it is the more similar to bacterial division.
Aside from cancer cells, many fully differentiated cell types no longer replicate so they leave the cell cycle and stay in G0 until their death. Thus removing the need for cellular checkpoints. An alternative model of the cell cycle response to DNA damage has also been proposed, known as the postreplication checkpoint. Checkpoint regulation plays an important role in an organism's development. In sexual reproduction, when egg fertilization occurs, when the sperm binds to the egg, it releases signalling factors that notify the egg that it has been fertilized.
Among other things, this induces the now fertilized oocyte to return from its previously dormant, G0, state back into the cell cycle and on to mitotic replication and division. In addition to p53, checkpoint regulators are being heavily researched for their roles in cancer growth and proliferation.
Fluorescence imaging of the cell cycle[ edit ] Fluorescent proteins visualize the cell cycle progression. Pioneering work by Atsushi Miyawaki and coworkers developed the fluorescent ubiquitination-based cell cycle indicator FUCCIwhich enables fluorescence imaging of the cell cycle. Note, these fusions are fragments that contain a nuclear localization signal and ubiquitination sites for degradationbut are not functional proteins.
The green fluorescent protein is made during the S, G2, or M phase and degraded during the G0 or G1 phase, while the orange fluorescent protein is made during the G0 or G1 phase and destroyed during the S, G2, or M phase.
Although the duration of cell cycle in tumor cells is equal to or longer than that of normal cell cycle, the proportion of cells that are in active cell division versus quiescent cells in G0 phase in tumors is much higher than that in normal tissue.
The cells which are actively undergoing cell cycle are targeted in cancer therapy as the DNA is relatively exposed during cell division and hence susceptible to damage by drugs or radiation. This fact is made use of in cancer treatment; by a process known as debulkinga significant mass of the tumor is removed which pushes a significant number of the remaining tumor cells from G0 to G1 phase due to increased availability of nutrients, oxygen, growth factors etc.
Phases of the cell cycle
Radiation or chemotherapy following the debulking procedure kills these cells which have newly entered the cell cycle. Stem cells in resting mouse skin may have a cycle time of more than hours.
Most of this difference is due to the varying length of G1, the most variable phase of the cycle. M and S do not vary much. In general, cells are most radiosensitive in late M and G2 phases and most resistant in late S phase.
For cells with a longer cell cycle time and a significantly long G1 phase, there is a second peak of resistance late in G1. The pattern of resistance and sensitivity correlates with the level of sulfhydryl compounds in the cell. Sulfhydryls are natural substances that protect cells from radiation damage and tend to be at their highest levels in S and at their lowest near mitosis.