Animal Cell Mitosis.This animation demonstrates the stages of mitosis in an animal cell.Updated November 2001.Feedback. Use the control buttons along the bottom to run the complete animation.Click on any intermediate stage for example, Anaphase, and see a representative still frame.Interphase Cells may appear inactive during this stage, but they are quite the opposite.This is the longest period of the complete cell cycle during which DNA replicates, the centrioles divide, and proteins are actively produced.For a complete description of the events during Interphase, read about the Cell Cycle.Prophase During this first mitotic stage, the nucleolus fades and chromatin replicated DNA and associated proteins condenses into chromosomes.Each replicated chromosome comprises two chromatids, both with the same genetic information.Microtubules of the cytoskeleton, responsible for cell shape, motility and attachment to other cells during interphase, disassemble.And the building blocks of these microtubules are used to grow the mitotic spindle from the region of the centrosomes.Prometaphase In this stage the nuclear envelope breaks down so there is no longer a recognizable nucleus.Some mitotic spindle fibers elongate from the centrosomes and attach to kinetochores, protein bundles at the centromere region on the chromosomes where sister chromatids are joined.Other spindle fibers elongate but instead of attaching to chromosomes, overlap each other at the cell center.Metaphase Tension applied by the spindle fibers aligns all chromosomes in one plane at the center of the cell.Anaphase Spindle fibers shorten, the kinetochores separate, and the chromatids daughter chromosomes are pulled apart and begin moving to the cell poles.Telophase The daughter chromosomes arrive at the poles and the spindle fibers that have pulled them apart disappear.Cytokinesis The spindle fibers not attached to chromosomes begin breaking down until only that portion of overlap is left.It is in this region that a contractile ring cleaves the cell into two daughter cells.Microtubules then reorganize into a new cytoskeleton for the return to interphase.Cancer cells reproduce relatively quickly in culture.In the Cancer Cell CAM compare the length of time these cells spend in interphase to that for mitosis to occur.Mitosis Wikipedia.Mitosis in an animal cell phases ordered counter clockwise.Onion Allium cells in different phases of the cell cycle enlarged 8.In cell biology, mitosis is a part of the cell cycle when replicated chromosomes are separated into two new nuclei.In general, mitosis division of the nucleus is preceded by the S stage of interphase during which the DNA is replicated and is often accompanied or followed by cytokinesis, which divides the cytoplasm, organelles and cell membrane into two new cells containing roughly equal shares of these cellular components.Mitosis and cytokinesis together define the mitotic M phase of an animal cell cyclethe 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 prophase, prometaphase, metaphase, anaphase, and telophase.During mitosis, the chromosomes, which have already duplicated, condense and attach to spindle fibers that pull one copy of each chromosome to opposite sides of the cell.The result is two genetically identical daughter nuclei.The rest of the cell may then continue to divide by cytokinesis to produce two daughter cells.Producing three or more daughter cells instead of normal two is a mitotic error called tripolar mitosis or multipolar mitosis direct cell triplication multiplication.Other errors during mitosis can induce apoptosis programmed cell death or cause mutations.Certain types of cancer can arise from such mutations.Mitosis occurs only in eukaryotic cells.Prokaryotic cells, which lack a nucleus, divide by a different process called binary fission.Mitosis varies between organisms.For example, animal cells undergo an open mitosis, where the nuclear envelope breaks down before the chromosomes separate, whereas fungi undergo a closed mitosis, where chromosomes divide within an intact cell nucleus.Most animal cells undergo a shape change, known as mitotic cell rounding, to adopt a near spherical morphology at the start of mitosis.Most human cells are produced by mitotic cell division.Important exceptions include the gametes sperm and egg cells which are produced by meiosis.DiscoveryeditGerman zoologist Otto Btschli might have claimed the discovery of the process presently known as mitosis,8 a term coined by Walther Flemming in 1.Mitosis was discovered in frog, rabbit, and cat cornea cells in 1.Polish histologist.Wacaw Mayzel in 1.The term is derived from the Greek word mitos warp thread.OvervieweditThe primary result of mitosis and cytokinesis is the transfer of a parent cells genome into two daughter cells.The genome is composed of a number of chromosomescomplexes of tightly coiled DNA that contain genetic information vital for proper cell function.Because each resultant daughter cell should be genetically identical to the parent cell, the parent cell must make a copy of each chromosome before mitosis.This occurs during the S phase of interphase.Chromosome duplication results in two identical sister chromatids bound together by cohesin proteins at the centromere.When mitosis begins, the chromosomes condense and become visible.In some eukaryotes, for example animals, the nuclear envelope, which segregates the DNA from the cytoplasm, disintegrates into small vesicles.The nucleolus, which makes ribosomes in the cell, also disappears.Microtubules project from opposite ends of the cell, attach to the centromeres, and align the chromosomes centrally within the cell.The microtubules then contract to pull the sister chromatids of each chromosome apart.Sister chromatids at this point are called daughter chromosomes. 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As the cell elongates, corresponding daughter chromosomes are pulled toward opposite ends of the cell and condense maximally in late anaphase.A new nuclear envelope forms around the separated daughter chromosomes, which decondense to form interphase nuclei.During mitotic progression, typically after the anaphase onset, the cell may undergo cytokinesis.In animal cells, a cell membrane pinches inward between the two developing nuclei to produce two new cells.In plant cells, a cell plate forms between the two nuclei.Cytokinesis does not always occur coenocytic a type of multinucleate condition cells undergo mitosis without cytokinesis.Phases of cell cycle and mitosiseditInterphaseeditThe mitotic phase is a relatively short period of the cell cycle.It alternates with the much longer interphase, where the cell prepares itself for the process of cell division.Interphase is divided into three phases G1 first gap, S synthesis, and G2 second gap.During all three parts of interphase, the cell grows by producing proteins and cytoplasmic organelles.However, chromosomes are replicated only during the S phase.Thus, a cell grows G1, continues to grow as it duplicates its chromosomes S, grows more and prepares for mitosis G2, and finally divides M before restarting the cycle.All these phases in the cell cycle are highly regulated by cyclins, cyclin dependent kinases, and other cell cycle proteins.The phases follow one another in strict order and there are checkpoints that give the cell cues to proceed from one phase to another.Cells may also temporarily or permanently leave the cell cycle and enter G0 phase to stop dividing.This can occur when cells become overcrowded density dependent inhibition or when they differentiate to carry out specific functions for the organism, as is the case for human heart muscle cells and neurons.Some G0 cells have the ability to re enter the cell cycle.Preprophase plant cellseditIn plant cells only, prophase is preceded by a pre prophase stage.In highly vacuolated plant cells, the nucleus has to migrate into the center of the cell before mitosis can begin.This is achieved through the formation of a phragmosome, a transverse sheet of cytoplasm that bisects the cell along the future plane of cell division.In addition to phragmosome formation, preprophase is characterized by the formation of a ring of microtubules and actin filaments called preprophase band underneath the plasma membrane around the equatorial plane of the future mitotic spindle.This band marks the position where the cell will eventually divide.The cells of higher plants such as the flowering plants lack centrioles instead, microtubules form a spindle on the surface of the nucleus and are then organized into a spindle by the chromosomes themselves, after the nuclear envelope breaks down.The preprophase band disappears during nuclear envelope breakdown and spindle formation in prometaphase.ProphaseeditDuring prophase, which occurs after G2 interphase, the cell prepares to divide by tightly condensing its chromosomes and initiating mitotic spindle formation.During interphase, the genetic material in the nucleus consists of loosely packed chromatin.At the onset of prophase, chromatin fibers condense into discrete chromosomes that are typically visible at high magnification through a light microscope.In this stage, chromosomes are long, thin and thread like.Each chromosome has two chromatids.The two chromatids are joined at the centromere.Gene transcription ceases during prophase and does not resume until late anaphase to early G1 phase.The nucleolus also disappears during early prophase.Condensing chromosomes.Interphase nucleus left, condensing chromosomes middle and condensed chromosomes right.Close to the nucleus of animal cells are structures called centrosomes, consisting of a pair of centrioles surrounded by a loose collection of proteins.The centrosome is the coordinating center for the cells microtubules.A cell inherits a single centrosome at cell division, which is duplicated by the cell before a new round of mitosis begins, giving a pair of centrosomes.The two centrosomes polymerize tubulin to help form a microtubule spindle apparatus.Motor proteins then push the centrosomes along these microtubules to opposite sides of the cell.Although centrosomes help organize microtubule assembly, they are not essential for the formation of the spindle apparatus, since they are absent from plants,1.PrometaphaseeditAt the beginning of prometaphase in animal cells, phosphorylation of nuclear lamins causes the nuclear envelope to disintegrate into small membrane vesicles.
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