cell cycle

Cell cycle

The succession of events that culminates in the asexual reproduction of a cell; also known as cell division cycle. In a typical cell cycle, the parent cell doubles its volume, mass, and complement of chromosomes, then sorts its doubled contents to opposite sides of the cell, and finally divides in half to yield two genetically identical offspring. Implicit in the term “cycle” is the idea that division brings the double-sized parent cell back to its original size and chromosome number, and ready to begin another cell cycle. This idea fits well with the behavior of many unicellular organisms, but for multicellular organisms the daughter cells may differ from their parent cell and from each other in terms of size, shape, and differentiation state.

The time required for completion of a eukaryotic cell cycle varies enormously from cell to cell. Embryonic cells that do not need to grow between divisions can complete a cell cycle in as little as 8 min, whereas cycling times of 10–24 h are typical of the most rapidly dividing somatic cells. Many somatic cells divide much less frequently; liver cells divide about once a year, and mature neurons never divide. Such cells may be thought of as temporarily or permanently withdrawing from the cell cycle.

Eukaryotic phases

The cell cycle is divided into two main parts: interphase and mitosis (see illustration). During interphase, the cell grows and replicates its chromosomes. Interphase accounts for all but an hour or two of a 24-h cell cycle, and is subdivided into three phases: gap phase 1 (G1), synthesis (S), and gap phase 2 (G2). Interphase is followed by mitosis (nuclear division) and cytokinesis (cell division). This relatively brief part of the cell cycle includes some of the most dramatic events in cell biology.

Phases of the eukaryotic cell cycle

G1 phase

Gap phase 1 begins at the completion of mitosis and cytokinesis and lasts until the beginning of S phase. This phase is generally the longest of the four cell cycle phases and is quite variable in length. During this phase, the cell chooses either to replicate its deoxyribonucleic acid (DNA) or to exit the cell cycle and enter a quiescent state (the G0 phase).

S phase

Replication of the chromosomes is restricted to one specific portion of interphase, called S phase (DNA synthesis phase), which typically lasts about 6 h. In mammalian cells, the start of S phase—the actual initiation of DNA synthesis—takes place several hours after the cell has committed to carrying out DNA synthesis. During S phase, each chromosome replicates exactly once to form a pair of physically linked sister chromatids. In animal cells, a pair of centrioles is also duplicated during S phase. See Chromosome, Genetics

G2 phase

The portion of interphase that follows S phase is called gap phase 2. Some cells can exit the cell cycle from G2 phase, just as they can from G1 phase.

M phase

M phase includes the overlapping processes of mitosis and cytokinesis. Mitosis is divided into five stages: prophase, prometaphase, metaphase, anaphase, and telophase. Cytokinesis usually begins during anaphase and ends at a point after the completion of mitosis. At the end of cytokinesis, the parent cell has formed its two G1 phase progeny and the cell is ready to repeat the cycle. See Cytokinesis, Mitosis

Control of cell cycle

The network of proteins that regulate DNA synthesis (G1/S), mitotic entry (G1/M), and mitotic exit (the transition from mitotic metaphase to anaphase and then out of mitosis) appears to be well conserved throughout eukaryotic evolution. At the heart of these cell cycle transtions is the periodic activation and inactivation of cyclin-dependent protein kinases. In addition, in multicellular eukaryotes, pathways regulating entry into and exit from the cell cycle entrain these central cyclin-dependent kinases to extrinsic signals.

cell cycle

[′sel ‚sī·kəl] (cell and molecular biology) In eukaryotic cells, the cycle of events consisting of cell division, including mitosis and cytokinesis, and interphase.

cell cycle

cycle

[si´k'l] a succession or recurring series of events.cardiac cycle a complete cardiac movement, or heart beat, including systole, diastole, and the intervening pause.

Cardiac cycle. From Applegate, 2000.cell cycle the cycle of biochemical and morphological events occurring in a reproducing cell population; it consists of the S phase, occurring toward the end of interphase, in which DNA is synthesized; the G₂ phase, a relatively quiescent period; the M phase, consisting of the four phases of mitosis; and the G₁ phase of interphase, which lasts until the S phase of the next cycle.citric acid cycle tricarboxylic acid cycle.estrous cycle the recurring periods of estrus in adult females of most mammalian species and the correlated changes in the reproductive tract from one period to another.hair cycle the successive phases of the production and then loss of hair, consisting of anagen, catagen, and telogen.Krebs cycle tricarboxylic acid cycle.menstrual cycle see menstrual cycle.ovarian cycle the sequence of physiologic changes in the ovary involved in ovulation; see also ovulation and reproduction.reproductive cycle the cycle of physiologic changes in the reproductive organs, from the time of fertilization of the ovum through gestation and childbirth; see also reproduction.sex cycle (sexual cycle) 1. the physiologic changes that recur regularly in the reproductive organs of nonpregnant female mammals.2. the period of sexual reproduction in an organism that also reproduces asexually.TCA cycle tricarboxylic acid cycle.tricarboxylic acid cycle the cyclic metabolic mechanism by which the complete oxidation of the acetyl portion of acetyl-coenzyme A is effected; the process is the chief source of mammalian energy, during which carbon chains of sugars, fatty acids, and amino acids are metabolized to yield carbon dioxide, water, and high-energy phosphate bonds. Called also citric acid cycle, Krebs cycle, and TCA cycle.

Central pathways of metabolism: How the body produces energy from the energy-containing nutrients using the tricarboxylic acid cycle. From Davis and Sherer, 1994.urea cycle a cyclic series of reactions that produce urea" >urea; it is a major route for removal of the ammonia produced in the metabolism of amino acids in the liver and kidney.

cell cy·cle

the periodic biochemical and structural events occurring during proliferation of cells such as in tissue culture; the cycle is divided into phases called G₀, Gap₁ (G₁), synthesis (S₁), Gap₂ (G₂), and mitosis (M). The period runs from one division to the next. Synonym(s): mitotic cycle

cell cycle

n. The series of events involving the growth, replication, and division of a eukaryotic cell.

cell cy·cle

(sel sī'kĕl) The periodic biochemical and structural events occurring during proliferation of cells, such as in tissue culture.

Fig. 96 Cell cycle . The interphase stages.

cell cycle

the series of stages through which a cell progresses when it is actively dividing. In EUKARYOTES, the cycle consists of three subdivisions of INTERPHASE (G1, S and G2) plus MITOSIS.

cell cy·cle

(sel sī'kĕl) The periodic biochemical and structural events occurring during proliferation of cells, such as in tissue culture.

单词	cell cycle
释义	cell cycle cell cycle n. The series of events involving the growth, replication, and division of a eukaryotic cell. cell cycle n (Genetics) the growth cycle of eukaryotic cells. It is divided into five stages, known as G0, in which the cell is quiescent, G1 and G2, in which it increases in size, S, in which it duplicates its DNA, and M, in which it undergoes mitosis and divides cell′ cy`cle n. the cycle of growth and asexual reproduction of a cell, consisting of interphase followed in actively dividing cells by prophase, metaphase, anaphase, and telophase. [1970–75] cell cycle Cell cycle The succession of events that culminates in the asexual reproduction of a cell; also known as cell division cycle. In a typical cell cycle, the parent cell doubles its volume, mass, and complement of chromosomes, then sorts its doubled contents to opposite sides of the cell, and finally divides in half to yield two genetically identical offspring. Implicit in the term “cycle” is the idea that division brings the double-sized parent cell back to its original size and chromosome number, and ready to begin another cell cycle. This idea fits well with the behavior of many unicellular organisms, but for multicellular organisms the daughter cells may differ from their parent cell and from each other in terms of size, shape, and differentiation state. The time required for completion of a eukaryotic cell cycle varies enormously from cell to cell. Embryonic cells that do not need to grow between divisions can complete a cell cycle in as little as 8 min, whereas cycling times of 10–24 h are typical of the most rapidly dividing somatic cells. Many somatic cells divide much less frequently; liver cells divide about once a year, and mature neurons never divide. Such cells may be thought of as temporarily or permanently withdrawing from the cell cycle. Eukaryotic phases The cell cycle is divided into two main parts: interphase and mitosis (see illustration). During interphase, the cell grows and replicates its chromosomes. Interphase accounts for all but an hour or two of a 24-h cell cycle, and is subdivided into three phases: gap phase 1 (G1), synthesis (S), and gap phase 2 (G2). Interphase is followed by mitosis (nuclear division) and cytokinesis (cell division). This relatively brief part of the cell cycle includes some of the most dramatic events in cell biology. Phases of the eukaryotic cell cycle G1 phase Gap phase 1 begins at the completion of mitosis and cytokinesis and lasts until the beginning of S phase. This phase is generally the longest of the four cell cycle phases and is quite variable in length. During this phase, the cell chooses either to replicate its deoxyribonucleic acid (DNA) or to exit the cell cycle and enter a quiescent state (the G0 phase). S phase Replication of the chromosomes is restricted to one specific portion of interphase, called S phase (DNA synthesis phase), which typically lasts about 6 h. In mammalian cells, the start of S phase—the actual initiation of DNA synthesis—takes place several hours after the cell has committed to carrying out DNA synthesis. During S phase, each chromosome replicates exactly once to form a pair of physically linked sister chromatids. In animal cells, a pair of centrioles is also duplicated during S phase. See Chromosome, Genetics G2 phase The portion of interphase that follows S phase is called gap phase 2. Some cells can exit the cell cycle from G2 phase, just as they can from G1 phase. M phase M phase includes the overlapping processes of mitosis and cytokinesis. Mitosis is divided into five stages: prophase, prometaphase, metaphase, anaphase, and telophase. Cytokinesis usually begins during anaphase and ends at a point after the completion of mitosis. At the end of cytokinesis, the parent cell has formed its two G1 phase progeny and the cell is ready to repeat the cycle. See Cytokinesis, Mitosis Control of cell cycle The network of proteins that regulate DNA synthesis (G1/S), mitotic entry (G1/M), and mitotic exit (the transition from mitotic metaphase to anaphase and then out of mitosis) appears to be well conserved throughout eukaryotic evolution. At the heart of these cell cycle transtions is the periodic activation and inactivation of cyclin-dependent protein kinases. In addition, in multicellular eukaryotes, pathways regulating entry into and exit from the cell cycle entrain these central cyclin-dependent kinases to extrinsic signals. cell cycle [′sel ‚sī·kəl] (cell and molecular biology) In eukaryotic cells, the cycle of events consisting of cell division, including mitosis and cytokinesis, and interphase. cell cycle cycle [si´k'l] a succession or recurring series of events.cardiac cycle a complete cardiac movement, or heart beat, including systole, diastole, and the intervening pause.Cardiac cycle. From Applegate, 2000.cell cycle the cycle of biochemical and morphological events occurring in a reproducing cell population; it consists of the S phase, occurring toward the end of interphase, in which DNA is synthesized; the G₂ phase, a relatively quiescent period; the M phase, consisting of the four phases of mitosis; and the G₁ phase of interphase, which lasts until the S phase of the next cycle.citric acid cycle tricarboxylic acid cycle.estrous cycle the recurring periods of estrus in adult females of most mammalian species and the correlated changes in the reproductive tract from one period to another.hair cycle the successive phases of the production and then loss of hair, consisting of anagen, catagen, and telogen.Krebs cycle tricarboxylic acid cycle.menstrual cycle see menstrual cycle.ovarian cycle the sequence of physiologic changes in the ovary involved in ovulation; see also ovulation and reproduction.reproductive cycle the cycle of physiologic changes in the reproductive organs, from the time of fertilization of the ovum through gestation and childbirth; see also reproduction.sex cycle (sexual cycle) 1. the physiologic changes that recur regularly in the reproductive organs of nonpregnant female mammals.2. the period of sexual reproduction in an organism that also reproduces asexually.TCA cycle tricarboxylic acid cycle.tricarboxylic acid cycle the cyclic metabolic mechanism by which the complete oxidation of the acetyl portion of acetyl-coenzyme A is effected; the process is the chief source of mammalian energy, during which carbon chains of sugars, fatty acids, and amino acids are metabolized to yield carbon dioxide, water, and high-energy phosphate bonds. Called also citric acid cycle, Krebs cycle, and TCA cycle. Central pathways of metabolism: How the body produces energy from the energy-containing nutrients using the tricarboxylic acid cycle. From Davis and Sherer, 1994.urea cycle a cyclic series of reactions that produce urea" >urea; it is a major route for removal of the ammonia produced in the metabolism of amino acids in the liver and kidney. cell cy·cle the periodic biochemical and structural events occurring during proliferation of cells such as in tissue culture; the cycle is divided into phases called G₀, Gap₁ (G₁), synthesis (S₁), Gap₂ (G₂), and mitosis (M). The period runs from one division to the next. Synonym(s): mitotic cycle cell cycle n. The series of events involving the growth, replication, and division of a eukaryotic cell. cell cy·cle (sel sī'kĕl) The periodic biochemical and structural events occurring during proliferation of cells, such as in tissue culture. Fig. 96 Cell cycle . The interphase stages. cell cycle the series of stages through which a cell progresses when it is actively dividing. In EUKARYOTES, the cycle consists of three subdivisions of INTERPHASE (G1, S and G2) plus MITOSIS. cell cy·cle (sel sī'kĕl) The periodic biochemical and structural events occurring during proliferation of cells, such as in tissue culture. LegalSeeCellFinancialSeeCycleThesaurusSeecycle
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cell cycle

cell cycle

cell cycle

cell′ cy`cle

cell cycle

Cell cycle

Eukaryotic phases

G1 phase

S phase

G2 phase

M phase

Control of cell cycle

cell cycle

cell cycle

cycle

cell cy·cle

cell cycle

cell cy·cle

cell cycle

cell cy·cle