11/8/2016 Cell cycle ­ Wikipedia Cell cycle From Wikipedia, the free encyclopedia The cell cycle or cell­division cycle is the series of events that take place in a cell leading to its division and duplication of its DNA (DNA replication) to produce two daughter cells. In bacteria, which lack a cell nucleus, the cell cycle is divided into the B, C, and D periods. The B period extends from the end of cell division to the beginning of DNA replication. DNA replication occurs during the C period. The D period refers to the stage between the end of DNA replication and the splitting of the bacterial cell into two daughter cells.[2] In cells with a nucleus, as in eukaryotes, the cell cycle is also divided into three periods: interphase, the mitotic (M) phase, and cytokinesis. During interphase, the cell grows, accumulating nutrients needed for mitosis, preparing it for cell division and duplicating its DNA. During the mitotic phase, the chromosomes separate. During the final stage, cytokinesis, the chromosomes and cytoplasm separate into two new daughter cells. To ensure the proper division of the cell, there are control mechanisms known as cell cycle checkpoints. Life Cycle of the cell The cell­division cycle is a vital process by which a single­celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. After cell division, each of the daughter cells begin the interphase of a new cycle. Although the various stages of interphase are not usually morphologically distinguishable, each phase of the cell cycle has a distinct set of specialized biochemical processes that prepare the cell for initiation of cell division. Contents 1 Cell cycle phases 1.1 G0 phase (Quiescence) Schematic of the cell 1.2 Interphase (Intermitosis) cycle. outer ring: I = 1.2.1 G1 Phase (Growth) Interphase, M = Mitosis; 1.2.2 S Phase (DNA replication) inner ring: M = Mitosis, 1.2.3 G2 Phase (Growth) G1 = Gap 1, G2 = Gap 2, 1.3 Mitotic phase (Chromosome separation) S = Synthesis; not in 1.4 Cytokinesis phase (Separation of all cell components) ring: G0 = Gap 2 Regulation of eukaryotic cell cycle 0/Resting.[1] 2.1 Role of cyclins and CDKs 2.1.1 General mechanism of cyclin­CDK interaction 2.1.2 Specific action of cyclin­CDK complexes 2.2 Inhibitors 2.3 Transcriptional regulatory network 2.4 DNA replication and DNA replication origin activity 3 Checkpoints 4 Fluorescence imaging of the cell cycle 5 Role in tumor formation Onion (Allium) cells in 6 See also 7 References different phases of the 8 Further reading cell cycle. Growth in an 9 External links organism is carefully controlled by regulating the cell cycle. Cell cycle phases https://en.wikipedia.org/wiki/Cell_cycle 1/6 11/8/2016 Cell cycle ­ Wikipedia State Description Abbreviation : A resting phase where the cell has left the cycle and has Gap 0 G 0 stopped dividing.Cell cycle starts with this phase. Quiescent Cells increase in size in Gap 1. The G1 checkpoint control senescent/resting Gap 1 G1 mechanism ensures that everything is ready for DNA phase synthesis. Synthesis S DNA replication occurs during this phase. Interphase During the gap between DNA synthesis and mitosis, the cell will continue to grow. The G2 checkpoint control mechanism Gap 2 G2 ensures that everything is ready to enter the M (mitosis) phase and divide. Cell growth stops at this stage and cellular energy is focused on the orderly division into two daughter cells. A checkpoint Cell division Mitosis M in the middle of mitosis (Metaphase Checkpoint) ensures that the cell is ready to complete cell division. G0 phase (Quiescence) G0 is a resting phase where the cell has left the cycle and has stopped dividing. The cell cycle starts with this phase. The word "post­mitotic" is sometimes used to refer to both quiescent and senescent cells. Non proliferative (non­dividing) cells in multicellular eukaryotes generally enter the quiescent G0 state from G1 and may remain quiescent for long periods of time, possibly indefinitely (as is often the case for neurons). This is very common for cells that are fully differentiated. Cellular senescence (death) occurs in response to DNA damage or degradation that would make a cell's progeny nonviable. Some cells enter the G0 phase semi­ permanently e.g., some liver, kidney, stomach cells. Many cells do not enter G0 and continue to divide throughout an organism's life, e.g. epithelial cells. Interphase (Intermitosis) Plant cell cycle Before a cell can enter cell division, it needs to take in nutrients. All of the preparations are done during interphase. Interphase is a series of changes that takes place in a newly formed cell and its nucleus, before it becomes capable of division again. It is also called preparatory phase or intermitosis. Previously it was called resting stage because there is no apparent activity related to cell division.Typically interphase lasts for at least 90% of the total time required for the cell cycle. Interphase proceeds in three stages, G1, S, and G2, followed by the cycle of mitosis and cytokinesis. The cell's nuclear chromosomes are duplicated during S phase. G1 Phase (Growth) The first phase within interphase, from the end of the previous M phase until the beginning of DNA synthesis, is called G1 (G indicating gap). It is also called the growth phase. During this phase, the biosynthetic activities of the cell, which are considerably slowed down during M phase, resume at a high rate. The duration of G1 is highly variable, even among different cells of the same Animal cell cycle species. In this phase, the cell increases its supply of proteins, increases the number of organelles (such as mitochondria, ribosomes), and grows in size. S Phase (DNA replication) The ensuing S phase starts when DNA replication commences; when it is completed, all of the chromosomes have been replicated, i.e., each chromosome has two (sister) chromatids. Thus, during this phase, the amount of DNA in the cell has effectively doubled, though the ploidy of the cell remains the same. During this phase, synthesis is completed as quickly as possible due to the exposed base pairs being sensitive to harmful external factors such as mutagens. G2 Phase (Growth) G2 phase is a period of protein synthesis and rapid cell growth to prepare the cell for mitosis. Mitotic phase (Chromosome separation) The relatively brief M phase consists of nuclear division (karyokinesis). It is a relatively short period of the cell cycle. M phase is complex and highly regulated. The sequence of events is divided into phases, corresponding to the completion of one set of activities and the start of the next. These phases are sequentially known as: prophase, metaphase, anaphase, telophase Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets in two nuclei.[3] During the process of mitosis the pairs of chromosomes condense and attach to fibers that pull the sister chromatids to opposite sides of the cell.[4] https://en.wikipedia.org/wiki/Cell_cycle 2/6 11/8/2016 Cell cycle ­ Wikipedia Mitosis occurs exclusively in eukaryotic cells, but occurs in different ways in different species. For example, animals undergo an "open" mitosis, where the nuclear envelope breaks down before the chromosomes separate, while fungi such as Aspergillus nidulans and Saccharomyces cerevisiae (yeast) undergo a "closed" mitosis, where chromosomes divide within an intact cell nucleus.[5] Prokaryotic cells, which lack a nucleus, divide by a process called binary fission. Cytokinesis phase (Separation of all cell components) Mitosis is immediately followed by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly equal shares of these cellular components. Mitosis and cytokinesis together define the division of the mother cell into two daughter cells, genetically identical to each other and to their parent cell. This accounts for approximately 10% of the cell cycle. Because cytokinesis usually occurs in conjunction with mitosis, "mitosis" is often used interchangeably with "M phase". However, there are many cells where mitosis and cytokinesis occur separately, forming single cells with multiple nuclei in a process called endoreplication. This occurs most notably among the fungi and slime moulds, but is found in various groups. Even in animals, cytokinesis and mitosis may occur independently, for instance during certain stages of fruit fly embryonic development.[6] Errors in mitosis can either kill a cell through apoptosis or cause mutations that may lead to cancer. Regulation of eukaryotic cell cycle Regulation of the cell cycle involves processes crucial to the survival of a cell, including the detection and repair of genetic damage as well as the prevention of uncontrolled cell division. The molecular events that Life timeline control the cell cycle are ordered and directional; that is, each process occurs in a sequential fashion and it is view • discuss • impossible to "reverse" the cycle. 0 — ←Earliest humans P Flowers h Mammals Role of cyclins and CDKs – a Dinosaurs n Land life r ­500 — ←Cambrian explosion Two key classes of regulatory molecules, cyclins and cyclin­dependent kinases z [7] c (CDKs), determine a cell's progress through the cell cycle. Leland H. Hartwell, – R. Timothy Hunt, and Paul M. Nurse won the 2001 Nobel Prize in Physiology or Multicellular [8] ­1000 — life Medicine for their discovery of these central molecules. Many of the genes encoding cyclins and CDKs are conserved among all eukaryotes, but in general ←Earliest sexual – P reproduction more complex organisms have more elaborate cell cycle control systems that r ­1500 — o incorporate more individual components.