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In
cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, ...
, mitosis () is a part of the
cell cycle The cell cycle, or cell-division cycle, is the series of events that take place in a cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, ...

cell cycle
in which replicated
chromosomes A chromosome is a long DNA molecule with part or all of the genome, genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by Chaperone (protein), chaperone proteins, bind to and D ...
are separated into two new nuclei. Cell division 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 (division of the nucleus) is preceded by the S stage of
interphase Interphase is the portion of the cell cycle that is not accompanied by gross changes under the microscope, and includes the G1, S and G2 phases. During interphase, the cell grows (G1), replicates its DNA (S) and prepares for mitosis (G2). A cell ...

interphase
(during which the DNA is replicated) and is often followed by
telophase Fluorescence micrograph of a human cell in telophase showing chromosomes (DNA) in blue, microtubules in green and kinetochores in pink Telophase (from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el ...

telophase
and
cytokinesis Cytokinesis () is the part of the cell division biological process, process during which the cytoplasm of a single eukaryotic cell divides into two daughter cells. Cytoplasmic division begins during or after the late stages of Mitosis, nuclear di ...

cytokinesis
; which divides the
cytoplasm In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, ...
,
organelle In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, M ...
s and
cell membrane cell membrane vs. Prokaryotes A prokaryote is a typically unicellular organism that lacks a nuclear membrane-enclosed cell nucleus, nucleus. The word ''prokaryote'' comes from the Greek language, Greek (, 'before') and (, 'nut' or 'kernel').C ...

cell membrane
of one cell into two new
cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religious recluse lives * Prison cell, a room used to hold peopl ...
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 Division or divider may refer to: Mathematics *Division (mathematics), the inverse of multiplication *Division algorithm, a method for computing the result of mathematical division Military *Division (military), a formation typically consisting o ...

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 File:3D-SIM-3 Prophase 3 color.jpg, 200px, Fluorescence microscope image of two mouse cell nuclei in prophase (scale bar is 5 μm). Prophase () is the first stage of cell division in both mitosis and meiosis. Beginning after interphase, DNA h ...

prophase
,
prometaphase Prometaphase is the phase of mitosis following prophase and preceding metaphase, in eukaryote, eukaryotic Somatic (biology), somatic Cell (biology), cells. In prometaphase, the nuclear membrane breaks apart into numerous "membrane vesicles", a ...

prometaphase
,
metaphase Metaphase () is a stage of mitosis In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical s ...

metaphase
,
anaphase Image:Anaphase IF.jpg, 300px, A cell during anaphase. Microtubules are visible in green. Anaphase (from the Ancient Greek, Greek ἀνά, "up" and φάσις, "stage"), is the stage of mitosis after the process of metaphase, when replicated chrom ...

anaphase
, and
telophase Fluorescence micrograph of a human cell in telophase showing chromosomes (DNA) in blue, microtubules in green and kinetochores in pink Telophase (from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el ...

telophase
. During mitosis, the chromosomes, which have already duplicated, condense and attach to spindle
fibers Fiber or fibre (from la, fibra, links=no) is a natural Nature, in the broadest sense, is the natural, physical, material world or universe The universe ( la, universus) is all of space and time and their contents, including ...

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. The different phases of mitosis can be visualized in real time, using
live cell imaging Live cell imaging is the study of living cells using time-lapse microscopy. It is used by scientists to obtain a better understanding of biological function through the study of cellular dynamics. Live cell imaging was pioneered in first decade ...
. Producing three or more daughter cells instead of the normal two is a mitotic error called tripolar mitosis or multipolar mitosis (direct cell triplication / multiplication). Other errors during mitosis can induce
apoptosis Apoptosis (from Ancient Greek wikt:ἀπόπτωσις, ἀπόπτωσις, ''apóptōsis'', "falling off") is a form of programmed cell death that occurs in multicellular organisms. Biochemistry, Biochemical events lead to characteristic cell ...

apoptosis
(programmed cell death) or cause
mutation A red tulip exhibiting a partially yellow petal due to a mutation in its genes In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processe ...
s. Certain types of
cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumor A benign tumor is a mass of cells Cell most often refers to: * Cell (biolo ...

cancer
can arise from such mutations. Mitosis occurs only in
eukaryotic Eukaryotes () are organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy (biology), tax ...

eukaryotic
cells.
Prokaryotic A prokaryote is a typically unicellular organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a syn ...
cells, which lack a nucleus, divide by a different process called
binary fission Binary may refer to: Science and technology Mathematics * Binary number In mathematics and digital electronics, a binary number is a number A number is a mathematical object used to counting, count, measurement, measure, and nominal ...

binary fission
. Mitosis varies between organisms. For example,
animal Animals (also called Metazoa) are organisms that form the Animalia. With few exceptions, animals , , are , can , and grow from a hollow sphere of , the , during . Over 1.5 million animal have been —of which around 1 million are —b ...

animal
cells undergo an "open" mitosis, where the
nuclear envelope The nuclear envelope, also known as the nuclear membrane, is made up of two lipid bilayer The lipid bilayer (or phospholipid bilayer) is a thin polar membrane A polarized membrane is a lipid bilayer, lipid membrane that has a positive electr ...

nuclear envelope
breaks down before the chromosomes separate, whereas
fungi A fungus (plural: fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as ...

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 Mitotic cell rounding is a shape change that occurs in most animal cell Eukaryotes () are organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of ...
, to adopt a near spherical morphology at the start of mitosis. Most human cells are produced by mitotic cell division. Important exceptions include the
gamete A gamete ( /ˈɡæmiːt/; from Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the foll ...
s –
sperm Sperm is the male reproductive Cell (biology), cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as ...

sperm
and
egg An egg is the organic vessel containing the in which an develops until it can survive on its own, at which point the animal hatches. An egg results from of an . Most s, (excluding s), and lay eggs, although some, such as s, do not. eg ...

egg
cells – which are produced by
meiosis spermatocyte, played back at 120× the recorded speed Meiosis (; from Greek language, Greek μείωσις, ''meiosis'', meaning "lessening") is a special type of cell division of germ cells in Sexual reproduction, sexually-reproducing organis ...

meiosis
.


Discovery

Numerous descriptions of
cell division Cell division is the process by which a parent cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religiou ...

cell division
were made during 18th and 19th centuries, with various degrees of accuracy. In 1835, the German botanist
Hugo von Mohl Hugo von Mohl FFRS HFRSE Fellowship of the Royal Society of Edinburgh (FRSE) is an award granted to individuals that the Royal Society of Edinburgh, Scotland's national academy of science and Literature, letters, judged to be "eminently distin ...

Hugo von Mohl
, described cell division in the
green algae The green algae (singular: green alga) are a large, informal grouping of algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic Photosynthesis is a process used by plants and other organisms to ...

green algae
'' Cladophora glomerata'', stating that multiplication of cells occurs through cell division. In 1838,
Matthias Jakob Schleiden Matthias Jakob Schleiden (; 1804–1881) was a German botanist Botany, also called , plant biology or phytology, is the science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific m ...

Matthias Jakob Schleiden
affirmed that the formation of new cells ''in their interior'' was a general law for cell multiplication in plants, a view later rejected in favour of Mohl model, due to contributions of
Robert Remak:''For the mathematician, Robert Remak (mathematician)'' Robert Remak (26 July 1815 – 29 August 1865) was a Jewish Jews ( he, יְהוּדִים ISO 259-2 , Israeli pronunciation ) or Jewish people are members of an ethnoreligious group ...

Robert Remak
and others. In animal cells, cell division with mitosis was discovered in frog, rabbit, and cat
cornea The cornea is the transparent Transparency, transparence or transparent most often refer to transparency and translucency, the physical property of allowing the transmission of light through a material. They may also refer to: Literal uses * ...

cornea
cells in 1873 and described for the first time by the Polish
histologist Histology, also known as microscopic anatomy or microanatomy, is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Mol ...
in 1875. Bütschli, Schneider and Fol might have also claimed the discovery of the process presently known as "mitosis".Ross, Anna E. "Human Anatomy & Physiology I: A Chronology of the Description of Mitosis". ''Christian Brothers University''. Retrieved 02 May 2018
link
.
In 1873, the German zoologist published data from observations on
nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a broa ...

nematode
s. A few years later, he discovered and described mitosis based on those observations. The term "mitosis", coined by
Walther Flemming Walther Flemming (21 April 1843 – 4 August 1905) was a German biologist Francesco Redi, the founder of biology, is recognized to be one of the greatest biologists of all time A biologist is a professional who has specialized knowledg ...

Walther Flemming
in 1882, is derived from the
Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of ...
word μίτος (''mitos'', "warp thread"). There are some alternative names for the process, e.g., "karyokinesis" (nuclear division), a term introduced by Schleicher in 1878, or "equational division", proposed by
August Weismann Prof August Friedrich Leopold Weismann FRS (For), HonFRSE, LLD (17 January 18345 November 1914) was a German evolutionary biologist. Ernst Mayr Ernst Walter Mayr (; 5 July 1904 – 3 February 2005) was one of the 20th century's leading ...

August Weismann
in 1887. However, the term "mitosis" is also used in a broad sense by some authors to refer to karyokinesis and cytokinesis together. Presently, "equational division" is more commonly used to refer to meiosis II, the part of meiosis most like mitosis.


Phases


Overview

The primary result of mitosis and cytokinesis is the transfer of a parent cell's
genome In the fields of molecular biology and genetics, a genome is all genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The genome includes both the genes (the coding regions) and the noncodin ...

genome
into two daughter cells. The genome is composed of a number of chromosomes—complexes of tightly coiled
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
that contain
genetic information A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monom ...

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 S phase (Synthesis Phase) is the phase of the cell cycle in which DNA is DNA replication, replicated, occurring between G1 phase, G1 phase and G2 phase, G2 phase. Since accurate duplication of the genome is critical to successful cell division, ...
of interphase. results in two identical ''
sister chromatids A sister chromatid refers to the identical copies (chromatids) formed by the DNA replication of a chromosome, with both copies joined together by a common centromere. In other words, a sister chromatid may also be said to be 'one-half' of the dup ...
'' bound together by
cohesin Cohesin is a protein complex that mediates sister chromatid cohesion, homologous recombination and Topologically associating domain, DNA looping. Cohesin is formed of SMC3, SMC1A, SMC1, RAD21, SCC1 and SCC3 (STAG1, SA1 or STAG2, SA2 in humans) ...

cohesin
proteins at the ''
centromere In this diagram of a duplicated chromosome, (2) identifies the centromere—the region that joins the two sister chromatids, or each half of the chromosome. In prophase of mitosis, specialized regions on centromeres called kinetochores attach chr ...
''. When mitosis begins, the chromosomes condense and become visible. In some eukaryotes, for example animals, the
nuclear envelope The nuclear envelope, also known as the nuclear membrane, is made up of two lipid bilayer The lipid bilayer (or phospholipid bilayer) is a thin polar membrane A polarized membrane is a lipid bilayer, lipid membrane that has a positive electr ...

nuclear envelope
, which segregates the DNA from the cytoplasm, disintegrates into small vesicles. The
nucleolus The nucleolus (, plural: nucleoli ) is the largest structure in the nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucl ...

nucleolus
, which makes ribosomes in the cell, also disappears.
Microtubule Microtubules are polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repeat unit, rep ...

Microtubule
s 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''. 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 cell Eukaryotes () are organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy (biology), tax ...

animal cell
s, a cell membrane pinches inward between the two developing nuclei to produce two new cells. In
plant cell Plant cells are eukaryotic Eukaryotes () are organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are class ...

plant cell
s, a
cell plate image:Phragmoplast.png, 300px, Phragmoplast and cell plate formation in a plant cell during cytokinesis. Left side: Phragmoplast forms and cell plate starts to assemble in the center of the cell. Towards the right: Phragmoplast enlarges in a donut- ...
forms between the two nuclei. Cytokinesis does not always occur; coenocytic (a type of multinucleate condition) cells undergo mitosis without cytokinesis.


Interphase

The mitotic phase is a relatively short period of the
cell cycle The cell cycle, or cell-division cycle, is the series of events that take place in a cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, ...

cell cycle
. It alternates with the much longer ''
interphase Interphase is the portion of the cell cycle that is not accompanied by gross changes under the microscope, and includes the G1, S and G2 phases. During interphase, the cell grows (G1), replicates its DNA (S) and prepares for mitosis (G2). A cell ...

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 S phase (Synthesis Phase) is the phase of the cell cycle in which DNA is DNA replication, replicated, occurring between G1 phase, G1 phase and G2 phase, G2 phase. Since accurate duplication of the genome is critical to successful cell division, ...
. 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 is a family of proteins that controls the progression of a cell through the cell cycle The cell cycle, or cell-division cycle, is the series of events that take place in a cell Cell most often refers to: * Cell (biology), the functi ...
,
cyclin-dependent kinases File:Cell Cycle 3.png, alt=, Schematic of the cell cycle. outer ring: I = Interphase, M = Mitosis; inner ring: M = Mitosis; G1 = G1 phase, Gap phase 1; S = S phase, Synthesis; G2 = G2 phase, Gap phase 2. Cyclin-dependent kinases (CDKs) are the fami ...
, and other cell cycle proteins. The phases follow one another in strict order and there are "
checkpoints Checkpoint may refer to: Places * Border checkpoint, a place on the land border between two states where travellers and/or goods are inspected * Security checkpoint, erected and enforced within contiguous areas under military or paramilitary contr ...
" 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 A neuron or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapse In the nervous system In biology Biology is the natural science that studies life and living ...

neurons
. Some G0 cells have the ability to re-enter the cell cycle. DNA double-strand breaks can be during interphase by two principal processes. The first process,
non-homologous end joining Non-homologous end joining (NHEJ) is a pathway that repairs double-strand breaks in DNA. NHEJ is referred to as "non-homologous" because the break ends are directly ligated without the need for a homologous template, in contrast to homology directe ...
(NHEJ), can join the two broken ends of DNA in the G1, S and G2 phases of interphase. The second process,
homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in Cell (biology), cellular organi ...

homologous recombination
al repair (HRR), is more accurate than NHEJ in repairing double-strand breaks. HRR is active during the S and G2 phases of interphase when
DNA replication In , DNA replication is the of producing two identical replicas of DNA from one original molecule. DNA replication occurs in all acting as the most essential part for . This is essential for cell division during growth and repair of damaged tis ...

DNA replication
is either partially accomplished or after it is completed, since HRR requires two adjacent homologs. Interphase helps prepare the cell for mitotic division. It dictates whether the mitotic cell division will occur. It carefully stops the cell from proceeding whenever the cell's DNA is damaged or has not completed an important phase. The interphase is very important as it will determine if mitosis completes successfully. It will reduce the amount of damaged cells produced and the production of cancerous cells. A miscalculation by the key Interphase proteins could be crucial as the latter could potentially create cancerous cells. Today, more research is being done to understand specifically how the phases stated above occur.


Mitosis


Preprophase (plant cells)

In 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 , 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 Actin is a protein family, family of Globular protein, globular multi-functional proteins that form microfilaments. It is found in essentially all Eukaryote, eukaryotic cells, where it may be present at a concentration of over 100 Micromolar, μ ...
filaments (called preprophase band) underneath the plasma membrane around the equatorial plane of the future mitotic . This band marks the position where the cell will eventually divide. The cells of higher plants (such as the
flowering plant Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greec ...

flowering plant
s) lack
centrioles In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, ...
; 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.


Prophase

During 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 Chromatin is a complex of DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecu ...
. At the onset of prophase, chromatin fibers condense into discrete chromosomes that are typically visible at high magnification through a
light microscope The optical microscope, also referred to as a light microscope, is a type of microscope that commonly uses visible spectrum, visible light and a system of lens (optics), lenses to generate magnified images of small objects. Optical microscopes ...
. 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 Transcription is the process of copying a segment of DNA into RNA. The segments of DNA transcribed into RNA molecules that can encode protein Proteins are large s and s that comprise one or more long chains of . Proteins perform a vast a ...
ceases during prophase and does not resume until late anaphase to early G1 phase. The
nucleolus The nucleolus (, plural: nucleoli ) is the largest structure in the nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucl ...

nucleolus
also disappears during early prophase. Close to the nucleus of animal cells are structures called
centrosome In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...

centrosome
s, consisting of a pair of
centriole In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, ...

centriole
s surrounded by a . The centrosome is the coordinating center for the cell's
microtubule Microtubules are polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repeat unit, rep ...

microtubule
s. A cell inherits a single centrosome at cell division, which is before a new round of mitosis begins, giving a pair of centrosomes. The two centrosomes polymerize
tubulin Tubulin in molecular biology can refer either to the tubulin protein superfamily of globular protein 300px, 3-dimensional structure of hemoglobin, a globular protein. Globular proteins or spheroproteins are spherical ("globe-like") protein ...

tubulin
to help form a .
Motor proteins 300px, microtubule.html"_;"title="Kinesin_walking_on_a_microtubule">Kinesin_walking_on_a_microtubule_using_protein_dynamics_on_Nanoscopic_scale.html" ;"title="protein_dynamics.html" ;"title="microtubule.html" ;"title="Kinesin walking on a microtub ...
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, and are not absolutely required for animal cell mitosis.


Prometaphase

At the beginning of prometaphase in animal cells, phosphorylation of
nuclear lamins Lamins, also known as nuclear lamins are fibrous proteins in Intermediate filament#Type V-nuclear lamins, type V intermediate filaments, providing structural function and Transcription (genetics), transcriptional regulation in the cell nucleus. Nuc ...
causes the
nuclear envelope The nuclear envelope, also known as the nuclear membrane, is made up of two lipid bilayer The lipid bilayer (or phospholipid bilayer) is a thin polar membrane A polarized membrane is a lipid bilayer, lipid membrane that has a positive electr ...

nuclear envelope
to disintegrate into small membrane
vesicles Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry), a supramolecular assembly of lipid molecules, like a cell membrane * Synaptic vesicle ; In human embryology * Vesicle (embryology), bulge-like features of ...
. As this happens, microtubules invade the nuclear space. This is called ''open mitosis'', and it occurs in some multicellular organisms. Fungi and some
protist A protist () is any eukaryotic Eukaryotes () are organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are c ...
s, such as
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic Photosynthesis is a process used by plants and other organisms to convert Conversion or convert may refer to: Arts, entertainment, and media * Co ...

algae
or trichomonads, undergo a variation called ''closed mitosis'' where the spindle forms inside the nucleus, or the microtubules penetrate the intact nuclear envelope. In late prometaphase, ''kinetochore microtubules'' begin to search for and attach to chromosomal
kinetochores A kinetochore (, ) is a disc-shaped protein structure associated with duplicated chromatids in eukaryote, eukaryotic cells where the spindle fibers attach during cell division to pull sister chromatids apart. The kinetochore assembles on the centr ...
. A ''kinetochore'' is a
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...

protein
aceous microtubule-binding structure that forms on the chromosomal centromere during late prophase. A number of ''polar microtubules'' find and interact with corresponding polar microtubules from the opposite centrosome to form the mitotic spindle. Although the kinetochore structure and function are not fully understood, it is known that it contains some form of
molecular motor Molecular motors are natural (biological) or artificial molecular machine A molecular machine, nanite, or nanomachine is a molecular component that produces quasi-mechanical movements (output) in response to specific stimuli (input). In cellu ...
. When a microtubule connects with the kinetochore, the motor activates, using energy from
ATP ATP may refer to: Companies and organizations * Association of Tennis Professionals * American Technical Publishers * ', a Danish pension * Armenia Tree Project * Association for Transpersonal Psychology * ATP architects engineers office * ATP ...

ATP
to "crawl" up the tube toward the originating centrosome. This motor activity, coupled with polymerisation and depolymerisation of microtubules, provides the pulling force necessary to later separate the chromosome's two chromatids.


Metaphase

After the microtubules have located and attached to the kinetochores in prometaphase, the two centrosomes begin pulling the chromosomes towards opposite ends of the cell. The resulting tension causes the chromosomes to align along the ''metaphase plate'' or ''equatorial plane'', an imaginary line that is centrally located between the two centrosomes (at approximately the midline of the cell). To ensure equitable distribution of chromosomes at the end of mitosis, the '' metaphase checkpoint'' guarantees that kinetochores are properly attached to the mitotic spindle and that the chromosomes are aligned along the metaphase plate. If the cell successfully passes through the metaphase checkpoint, it proceeds to anaphase.


Anaphase

During ''anaphase A'', the
cohesin Cohesin is a protein complex that mediates sister chromatid cohesion, homologous recombination and Topologically associating domain, DNA looping. Cohesin is formed of SMC3, SMC1A, SMC1, RAD21, SCC1 and SCC3 (STAG1, SA1 or STAG2, SA2 in humans) ...

cohesin
s that bind sister chromatids together are cleaved, forming two identical daughter chromosomes. Shortening of the kinetochore microtubules pulls the newly formed daughter chromosomes to opposite ends of the cell. During ''anaphase B'', polar microtubules push against each other, causing the cell to elongate. In late anaphase,
chromosome A chromosome is a long DNA molecule with part or all of the genome, genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by Chaperone (protein), chaperone proteins, bind to and ...

chromosome
s also reach their overall maximal condensation level, to help
chromosome segregation A chromosome is a long DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A mole ...
and the re-formation of the nucleus. In most animal cells, anaphase A precedes anaphase B, but some vertebrate egg cells demonstrate the opposite order of events.


Telophase

Telophase (from the
Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of ...
word ''τελος'' meaning "end") is a reversal of prophase and prometaphase events. At telophase, the polar microtubules continue to lengthen, elongating the cell even more. If the nuclear envelope has broken down, a new nuclear envelope forms using the membrane vesicles of the parent cell's old nuclear envelope. The new envelope forms around each set of separated daughter chromosomes (though the membrane does not enclose the centrosomes) and the nucleolus reappears. Both sets of chromosomes, now surrounded by new nuclear membrane, begin to "relax" or decondense. Mitosis is complete. Each daughter nucleus has an identical set of chromosomes. Cell division may or may not occur at this time depending on the organism.


Cytokinesis

Cytokinesis is not a phase of mitosis, but rather a separate process necessary for completing cell division. In animal cells, a
cleavage furrow of a cell, the cleavage furrow has nearly completely divided the cell. Image:Unk.cilliate.jpg, Cilliate undergoing the last processes of binary fission, with the cleavage furrow being clearly visible. In cell biology, the cleavage furrow is the in ...
(pinch) containing a contractile ring, develops where the metaphase plate used to be, pinching off the separated nuclei. In both animal and plant cells, cell division is also driven by vesicles derived from the
Golgi apparatus The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that stu ...

Golgi apparatus
, which move along microtubules to the middle of the cell. In plants, this structure coalesces into a cell plate at the center of the
phragmoplast image:Phragmoplast.png, 300px, Phragmoplast and cell plate formation in a plant cell during cytokinesis. Left side: Phragmoplast forms and cell plate starts to assemble in the center of the cell. Towards the right: Phragmoplast enlarges in a donut-s ...

phragmoplast
and develops into a cell wall, separating the two nuclei. The phragmoplast is a microtubule structure typical for higher plants, whereas some green algae use a microtubule array during cytokinesis. Each daughter cell has a complete copy of the genome of its parent cell. The end of cytokinesis marks the end of the M-phase. There are many cells where mitosis and cytokinesis occur separately, forming single cells with multiple nuclei. The most notable occurrence of this is among the
fungi A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ...

fungi
,
slime mold Slime mold or slime mould is an informal name given to several kinds of unrelated organisms that can live freely as single cells, but can aggregate together to form multicellular reproductive structures. Slime molds were formerly classified ...

slime mold
s, and coenocytic algae, but the phenomenon is found in various other organisms. Even in animals, cytokinesis and mitosis may occur independently, for instance during certain stages of embryonic development.


Function

Mitosis's "
function Function or functionality may refer to: Computing * Function key A function key is a key on a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern comp ...
" or significance relies on the maintenance of the chromosomal set; each formed cell receives chromosomes that are alike in composition and equal in number to the chromosomes of the parent cell. Mitosis occurs in the following circumstances: *Development and growth: The number of cells within an organism increases by mitosis. This is the basis of the development of a multicellular body from a single cell, i.e.,
zygote A zygote (, ) is a eukaryotic Eukaryotes () are organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are ...

zygote
and also the basis of the growth of a
multicellular A multicellular organism is an organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular ...

multicellular
body. *Cell replacement: In some parts of the body, e.g. skin and digestive tract, cells are constantly sloughed off and replaced by new ones. New cells are formed by mitosis and so are exact copies of the cells being replaced. In like manner,
red blood cells Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...

red blood cells
have a short lifespan (only about 4 months) and new RBCs are formed by mitosis . *Regeneration: Some organisms can regenerate body parts. The production of new cells in such instances is achieved by mitosis. For example,
starfish Starfish or sea stars are star-shaped In mathematics, a Set (mathematics), set S in the Euclidean space \R^n is called a star domain (or star-convex set, star-shaped set or radially convex set) if there exists an s_0 \in S such that for ...

starfish
regenerate lost arms through mitosis. *Asexual reproduction: Some organisms produce genetically similar offspring through
asexual reproduction Asexual reproduction is a type of reproduction Reproduction (or procreation or breeding) is the biological process Biological processes are those processes that are vital for an organism In biology, an organism (from Ancient Gree ...
. For example, the hydra reproduces asexually by budding. The cells at the surface of hydra undergo mitosis and form a mass called a bud. Mitosis continues in the cells of the bud and this grows into a new individual. The same division happens during asexual reproduction or
vegetative propagation '' Bryophyllum daigremontianum'' produces plantlets along the margins of its leaves. When they are mature enough, they drop off and root in any suitable soil beneath. Vegetative reproduction (also known as vegetative propagation, vegetative ...
in plants.


Variations


Forms of mitosis

The mitosis process in the cells of eukaryotic organisms follows a similar pattern, but with variations in three main details. "Closed" and "open" mitosis can be distinguished on the basis of
nuclear envelope The nuclear envelope, also known as the nuclear membrane, is made up of two lipid bilayer The lipid bilayer (or phospholipid bilayer) is a thin polar membrane A polarized membrane is a lipid bilayer, lipid membrane that has a positive electr ...

nuclear envelope
remaining intact or breaking down. An intermediate form with partial degradation of the nuclear envelope is called "semiopen" mitosis. With respect to the symmetry of the
spindle apparatus In cell biology, the spindle apparatus (or mitotic spindle) refers to the cytoskeletal structure of eukaryotic cells that forms during cell division to separate sister chromatids between daughter Cell (biology), cells. It is referred to as the m ...

spindle apparatus
during metaphase, an approximately axially symmetric (centered) shape is called "orthomitosis", distinguished from the eccentric spindles of "pleuromitosis", in which mitotic apparatus has bilateral symmetry. Finally, a third criterion is the location of the central spindle in case of closed pleuromitosis: "extranuclear" (spindle located in the cytoplasm) or "intranuclear" (in the nucleus). File:Mitosis classification closed intranuclear pleuromitoses.svg, closed
intranuclear
pleuromitosis File:Mitosis classification closed extranuclear pleuromitoses.svg, closed
extranuclear
pleuromitosis File:Mitosis classification closed orthomitoses.svg, closed
orthomitosis File:Mitosis classification semiopen pleuromitoses.svg, semiopen
pleuromitosis File:Mitosis classification semiopen orthomitoses.svg, semiopen
orthomitosis File:Mitosis classification open orthomitoses.svg, open
orthomitosis
Nuclear division takes place only in cells of organisms of the
eukaryotic Eukaryotes () are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interact ...
domain, as
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
and
archaea Archaea ( ; singular archaeon ) constitute a domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a pa ...

archaea
have no nucleus. Bacteria and archaea undergo a different type of division. Within each of the eukaryotic supergroups, mitosis of the open form can be found, as well as closed mitosis, except for Excavata, which show exclusively closed mitosis. Following, the occurrence of the forms of mitosis in eukaryotes: *''Closed intranuclear pleuromitosis'' is typical of Foraminifera, some Prasinophyceae, Prasinomonadida, some Kinetoplastida, the Oxymonadida, the Haplosporidia, many fungi (chytrids, oomycetes, zygomycetes, ascomycetes), and some Radiolaria (Spumellaria and Acantharea, Acantharia); it seems to be the most primitive type. *''Closed extranuclear pleuromitosis'' occurs in Trichomonadida and Dinoflagellata. * ''Closed orthomitosis'' is found among diatoms, ciliates, some Microsporidia, unicellular yeasts and some multicellular
fungi A fungus (plural: fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as ...

fungi
. *''Semiopen pleuromitosis'' is typical of most Apicomplexa. *''Semiopen orthomitosis'' occurs with different variants in some amoebae (Lobosa) and some green flagellates (e.g., Raphidophyte, Raphidophyta or ''Volvox''). *''Open orthomitosis'' is typical in mammals and other Metazoa, and in land plants; but it also occurs in some protists.


Errors and other variations

Errors can occur during mitosis, especially during early embryonic development in humans. During each step of mitosis, there are normally checkpoints as well that control the normal outcome of mitosis. But, occasionally to almost rarely, mistakes will happen. Mitotic errors can create aneuploidy, aneuploid cells that have too few or too many of one or more chromosomes, a condition associated with
cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumor A benign tumor is a mass of cells Cell most often refers to: * Cell (biolo ...

cancer
. Early human embryos, cancer cells, infected or intoxicated cells can also suffer from pathological division into three or more daughter cells (tripolar or multipolar mitosis), resulting in severe errors in their chromosomal complements. In ''nondisjunction'', sister chromatids fail to separate during anaphase. One daughter cell receives both sister chromatids from the nondisjoining chromosome and the other cell receives none. As a result, the former cell gets three copies of the chromosome, a condition known as ''trisomy'', and the latter will have only one copy, a condition known as ''monosomy''. On occasion, when cells experience nondisjunction, they fail to complete cytokinesis and retain both nuclei in one cell, resulting in binucleated cells. ''Anaphase lag'' occurs when the movement of one chromatid is impeded during anaphase. This may be caused by a failure of the mitotic spindle to properly attach to the chromosome. The lagging chromatid is excluded from both nuclei and is lost. Therefore, one of the daughter cells will be monosomic for that chromosome. ''Endoreduplication'' (or endoreplication) occurs when chromosomes duplicate but the cell does not subsequently divide. This results in polyploid cells or, if the chromosomes duplicates repeatedly, polytene chromosomes. Endoreduplication is found in many species and appears to be a normal part of developmental biology, development. Endomitosis is a variant of endoreduplication in which cells replicate their chromosomes during S phase and enter, but prematurely terminate, mitosis. Instead of being divided into two new daughter nuclei, the replicated chromosomes are retained within the original nucleus. The cells then re-enter G1 and S phase and replicate their chromosomes again. This may occur multiple times, increasing the chromosome number with each round of replication and endomitosis. Platelet-producing megakaryocytes go through endomitosis during cell differentiation. ''Amitosis'' in ciliates and in animal placental tissues results in a random distribution of parental alleles. ''Karyokinesis without cytokinesis'' originates multinucleated cells called coenocytes.


Diagnostic marker

In histopathology, the mitosis rate is an important parameter in various types of tissue samples, for diagnosis as well as to further specify the aggressiveness of tumors. For example, there is routinely a quantification of Breast cancer classification#Mitotic count, mitotic count in breast cancer classification. The mitoses must be counted in an area of the highest mitotic activity. Visually identifying these areas, is difficult in tumors with very high mitotic activity. Also, the detection of atypical forms of mitosis can be used both as a diagnostic and prognostic marker. For example, ''lag-type mitosis'' (non-attached condensed
chromatin Chromatin is a complex of DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecu ...
in the area of the mitotic figure) indicates high risk human papillomavirus infection-related Cervical cancer. File:Normal versus atypical mitosis.jpg, Normal and atypical forms of mitosis in cancer cells. A, normal mitosis; B, chromatin bridge; C, multipolar mitosis; D, ring mitosis; E, dispersed mitosis; F, asymmetrical mitosis; G, lag-type mitosis; and H, micronuclei. H&E stain.


Related cell processes


Cell rounding

In animal tissue, most cells round up to a near-spherical shape during mitosis. In epithelia and epidermis, an efficient rounding process is correlated with proper mitotic spindle alignment and subsequent correct positioning of daughter cells. Moreover, researchers have found that if rounding is heavily suppressed it may result in spindle defects, primarily pole splitting and failure to efficiently capture
chromosomes A chromosome is a long DNA molecule with part or all of the genome, genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by Chaperone (protein), chaperone proteins, bind to and D ...
. Therefore,
mitotic cell rounding Mitotic cell rounding is a shape change that occurs in most animal cell Eukaryotes () are organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of ...
is thought to play a protective role in ensuring accurate mitosis. Rounding forces are driven by reorganization of F-actin and myosin (actomyosin) into a contractile homogeneous cell cortex that 1) rigidifies the cell periphery and 2) facilitates generation of intracellular hydrostatic pressure (up to 10 fold higher than
interphase Interphase is the portion of the cell cycle that is not accompanied by gross changes under the microscope, and includes the G1, S and G2 phases. During interphase, the cell grows (G1), replicates its DNA (S) and prepares for mitosis (G2). A cell ...

interphase
). The generation of intracellular pressure is particularly critical under confinement, such as would be important in a tissue scenario, where outward forces must be produced to round up against surrounding cells and/or the extracellular matrix. 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. Due to its importance in mitosis, the molecular components and dynamics of the mitotic Cell cortex, actomyosin cortex is an area of active research.


Mitotic recombination

Mitotic cells irradiated with X-rays in the G1 phase of the
cell cycle The cell cycle, or cell-division cycle, is the series of events that take place in a cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, ...

cell cycle
repair recombinogenic DNA damage (naturally occurring), DNA damages primarily by Homologous recombination, recombination between homologous chromosomes. Mitotic cells irradiated in the G2 phase repair such damages preferentially by sister chromatid exchange, sister-chromatid recombination. Mutations in genes encoding enzymes employed in recombination cause cells to have increased sensitivity to being killed by a variety of DNA damaging agents. These findings suggest that mitotic recombination is an adaptation for repairing DNA damages including those that are potentially lethal.


Evolution

There are prokaryotic Homology (biology), homologs of all the key molecules of eukaryotic mitosis (e.g., actins, tubulins). Being a universal eukaryotic property, mitosis probably arose at the base of the eukaryotic tree. As mitosis is less complex than
meiosis spermatocyte, played back at 120× the recorded speed Meiosis (; from Greek language, Greek μείωσις, ''meiosis'', meaning "lessening") is a special type of cell division of germ cells in Sexual reproduction, sexually-reproducing organis ...

meiosis
, meiosis may have arisen after mitosis. However, sexual reproduction involving meiosis is also a primitive characteristic of eukaryotes.Bernstein, H., Bernstein, C. Evolutionary origin and adaptive function of meiosis. In “Meiosis”, Intech Publ (Carol Bernstein and Harris Bernstein editors), Chapter 3: 41-75 (2013). Thus meiosis and mitosis may both have evolved, in parallel, from ancestral prokaryotic processes. While in Fission (biology), bacterial cell division, after DNA replication, duplication of DNA, two circular chromosomes are attached to a special region of the cell membrane, eukaryotic mitosis is usually characterized by the presence of many linear chromosomes, whose kinetochores attaches to the microtubules of the spindle. In relation to the forms of mitosis, closed intranuclear pleuromitosis seems to be the most primitive type, as it is more similar to bacterial division.


Gallery

Mitotic cells can be visualized microscopically by staining (biology), staining them with fluorescent antibodies and dyes.


See also

* Aneuploidy * Binary fission * Chromosome abnormality * Cytoskeleton * Meiosis * Mitogen * Mitosis Promoting Factor * Mitotic bookmarking * Motor protein


References


Further reading

* * * * * *


External links


A Flash animation comparing Mitosis and Meiosis

Khan Academy, lecture

Studying Mitosis in Cultured Mammalian Cells

General K-12 classroom resources for Mitosis

The Cell-Cycle Ontology

WormWeb.org: Interactive Visualization of the ''C. elegans'' Cell Lineage
– Visualize the entire cell lineage tree and all of the cell divisions of the nematode ''C. elegans'' {{Authority control Mitosis, Cell cycle Articles containing video clips 1835 in science