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Metaphase
Metaphase ( and ) is a stage of mitosis in the eukaryotic cell cycle in which chromosomes are at their second-most condensed and coiled stage (they are at their most condensed in anaphase). These chromosomes, carrying genetic information, align in the equator of the cell before being separated into each of the two daughter cells. Metaphase accounts for approximately 4% of the cell cycle's duration. Preceded by events in prometaphase and followed by anaphase, microtubules formed in prophase have already found and attached themselves to kinetochores in metaphase. In metaphase, the centromeres of the chromosomes convene themselves on the ''metaphase plate'' (or ''equatorial plate''), an imaginary line that is equidistant from the two centrosome poles. This even alignment is due to the counterbalance of the pulling powers generated by the opposing kinetochore microtubules, analogous to a tug-of-war between two people of equal strength, ending with the destruction of B c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spindle Checkpoint
The spindle checkpoint, also known as the metaphase-to-anaphase transition, the spindle assembly checkpoint (SAC), the metaphase checkpoint, or the mitotic checkpoint, is a cell cycle checkpoint during mitosis or meiosis that prevents the separation of the duplicated chromosomes (anaphase) until each chromosome is properly attached to the spindle. To achieve proper segregation, the two kinetochores on the sister chromatids must be attached to opposite spindle poles (bipolar orientation). Only this pattern of attachment will ensure that each daughter cell receives one copy of the chromosome. The defining biochemical feature of this checkpoint is the stimulation of the anaphase-promoting complex by M-phase cyclin-CDK complexes, which in turn causes the proteolytic destruction of cyclins and proteins that hold the sister chromatids together. Overview and importance The beginning of metaphase is characterized by the connection of the microtubules to the kinetochores of the ch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metaphase
Metaphase ( and ) is a stage of mitosis in the eukaryotic cell cycle in which chromosomes are at their second-most condensed and coiled stage (they are at their most condensed in anaphase). These chromosomes, carrying genetic information, align in the equator of the cell before being separated into each of the two daughter cells. Metaphase accounts for approximately 4% of the cell cycle's duration. Preceded by events in prometaphase and followed by anaphase, microtubules formed in prophase have already found and attached themselves to kinetochores in metaphase. In metaphase, the centromeres of the chromosomes convene themselves on the ''metaphase plate'' (or ''equatorial plate''), an imaginary line that is equidistant from the two centrosome poles. This even alignment is due to the counterbalance of the pulling powers generated by the opposing kinetochore microtubules, analogous to a tug-of-war between two people of equal strength, ending with the destruction of B c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prometaphase
Prometaphase is the phase of mitosis following prophase and preceding metaphase, in eukaryotic somatic cells. In prometaphase, the nuclear membrane breaks apart into numerous "membrane vesicles", and the chromosomes inside form protein structures called kinetochores. Kinetochore microtubules emerging from the centrosomes at the poles (ends) of the spindle reach the chromosomes and attach to the kinetochores, throwing the chromosomes into agitated motion. Other spindle microtubules make contact with microtubules coming from the opposite pole. Forces exerted by protein "motors" associated with spindle microtubules move the chromosomes toward the centre of the cell. Prometaphase is not always presented as a distinct part of mitosis. In sources that do not use the term, the events described here are instead assigned to late prophase and early metaphase. Types of microtubules The microtubules are composed of two types, ''kinetochore microtubules'' and ''non-kinetochore microtub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metaphase Chromosomes
Metaphase ( and ) is a stage of mitosis in the eukaryotic cell cycle in which chromosomes are at their second-most condensed and coiled stage (they are at their most condensed in anaphase). These chromosomes, carrying genetic information, align in the equator of the cell before being separated into each of the two daughter cells. Metaphase accounts for approximately 4% of the cell cycle's duration. Preceded by events in prometaphase and followed by anaphase, microtubules formed in prophase have already found and attached themselves to kinetochores in metaphase. In metaphase, the centromeres of the chromosomes convene themselves on the ''metaphase plate'' (or ''equatorial plate''), an imaginary line that is equidistant from the two centrosome poles. This even alignment is due to the counterbalance of the pulling powers generated by the opposing kinetochore microtubules, analogous to a tug-of-war between two people of equal strength, ending with the destruction of B cyclin. In c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mitosis
In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is maintained. Therefore, mitosis is also known as equational division. In general, mitosis is preceded by S phase of interphase (during which DNA replication occurs) and is often followed by telophase and cytokinesis; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. The different stages of mitosis altogether define the mitotic (M) phase of an animal cell cycle—the division of the mother cell into two daughter cells genetically identical to each other. The process of mitosis is divided into stages corresponding to the completion of one set of activities and the start of the next. These stages are preprophase (specific to plant cells), propha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kinetochore
A kinetochore (, ) is a disc-shaped protein structure associated with duplicated chromatids in eukaryotic cells where the spindle fibers attach during cell division to pull sister chromatids apart. The kinetochore assembles on the centromere and links the chromosome to microtubule polymers from the mitotic spindle during mitosis and meiosis. The term kinetochore was first used in a footnote in a 1934 Cytology book by Lester W. Sharp and commonly accepted in 1936. Sharp's footnote reads: "The convenient term ''kinetochore'' (= movement place) has been suggested to the author by J. A. Moore", likely referring to John Alexander Moore who had joined Columbia University as a freshman in 1932. Monocentric organisms, including vertebrates, fungi, and most plants, have a single centromeric region on each chromosome which assembles a single, localized kinetochore. Holocentric organisms, such as nematodes and some plants, assemble a kinetochore along the entire length of a chromosome. K ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anaphase-promoting Complex
Anaphase-promoting complex (also called the cyclosome or APC/C) is an E3 ubiquitin ligase that marks target cell cycle proteins for degradation by the 26S proteasome. The APC/C is a large complex of 11–13 subunit proteins, including a cullin (Apc2) and RING (Apc11) subunit much like SCF. Other parts of the APC/C have unknown functions but are highly conserved. It was the discovery of the APC/C (and SCF) and their key role in eukaryotic cell-cycle regulation that established the importance of ubiquitin-mediated proteolysis in cell biology. Once perceived as a system exclusively involved in removing damaged protein from the cell, ubiquitination and subsequent protein degradation by the proteasome is now perceived as a universal regulatory mechanism for signal transduction whose importance approaches that of protein phosphorylation. In 2014, the APC/C was mapped in 3D at a resolution of less than a nanometre, which also uncovered its secondary structure. This finding ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are the histones. These proteins, aided by chaperone proteins, bind to and condense the DNA molecule to maintain its integrity. These chromosomes display a complex three-dimensional structure, which plays a significant role in transcriptional regulation. Chromosomes are normally visible under a light microscope only during the metaphase of cell division (where all chromosomes are aligned in the center of the cell in their condensed form). Before this happens, each chromosome is duplicated ( S phase), and both copies are joined by a centromere, resulting either in an X-shaped structure (pictured above), if the centromere is located equatorially, or a two-arm structure, if the centromere is located distally. The joined copies are now c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Karyotype
A karyotype is the general appearance of the complete set of metaphase chromosomes in the cells of a species or in an individual organism, mainly including their sizes, numbers, and shapes. Karyotyping is the process by which a karyotype is discerned by determining the chromosome complement of an individual, including the number of chromosomes and any abnormalities. A karyogram or idiogram is a graphical depiction of a karyotype, wherein chromosomes are organized in pairs, ordered by size and position of centromere for chromosomes of the same size. Karyotyping generally combines light microscopy and photography, and results in a photomicrographic (or simply micrographic) karyogram. In contrast, a schematic karyogram is a designed graphic representation of a karyotype. In schematic karyograms, just one of the sister chromatids of each chromosome is generally shown for brevity, and in reality they are generally so close together that they look as one on photomicrographs as well ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cytogenetics
Cytogenetics is essentially a branch of genetics, but is also a part of cell biology/cytology (a subdivision of human anatomy), that is concerned with how the chromosomes relate to cell behaviour, particularly to their behaviour during mitosis and meiosis. Techniques used include karyotyping, analysis of G-banded chromosomes, other cytogenetic banding techniques, as well as molecular cytogenetics such as fluorescent ''in situ'' hybridization (FISH) and comparative genomic hybridization (CGH). History Beginnings Chromosomes were first observed in plant cells by Carl Nägeli in 1842. Their behavior in animal (salamander) cells was described by Walther Flemming, the discoverer of mitosis, in 1882. The name was coined by another German anatomist, von Waldeyer in 1888. The next stage took place after the development of genetics in the early 20th century, when it was appreciated that the set of chromosomes (the karyotype) was the carrier of the genes. Levitsky seems to have be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cell Cycle
The cell cycle, or cell-division cycle, is the series of events that take place in a cell that cause it to divide into two daughter cells. These events include the duplication of its DNA (DNA replication) and some of its organelles, and subsequently the partitioning of its cytoplasm, chromosomes and other components into two daughter cells in a process called cell division. In cells with nuclei ( eukaryotes, i.e., animal, plant, fungal, and protist cells), the cell cycle is divided into two main stages: interphase and the mitotic (M) phase (including mitosis and cytokinesis). During interphase, the cell grows, accumulating nutrients needed for mitosis, and replicates its DNA and some of its organelles. During the mitotic phase, the replicated chromosomes, organelles, and cytoplasm separate into two new daughter cells. To ensure the proper replication of cellular components and division, there are control mechanisms known as cell cycle checkpoints after each of the key s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cyclin
Cyclin is a family of proteins that controls the progression of a cell through the cell cycle by activating cyclin-dependent kinase (CDK) enzymes or group of enzymes required for synthesis of cell cycle. Etymology Cyclins were originally discovered by R. Timothy Hunt in 1982 while studying the cell cycle of sea urchins. In an interview for "The Life Scientific" (aired on 13/12/2011) hosted by Jim Al-Khalili, R. Timothy Hunt explained that the name "cyclin" was originally named after his hobby cycling. It was only after the naming did its importance in the cell cycle become apparent. As it was appropriate the name stuck. R. Timothy Hunt: "By the way, the name cyclin, which I coined, was really a joke, it's because I liked cycling so much at the time, but they did come and go in the cell..." Function Cyclins were originally named because their concentration varies in a cyclical fashion during the cell cycle. (Note that the cyclins are now classified according to their co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
