Fission (biology)

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Fission, in biology, is the division of a single entity into two or more parts and the regeneration of those parts to separate entities resembling the original. The object experiencing fission is usually a cell, but the term may also refer to how organisms, bodies, populations, or species split into discrete parts. [1] [2] [3] The fission may be binary fission, in which a single organism produces two parts, or multiple fission, in which a single entity produces multiple parts.

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Binary fission

Schematic diagram of cellular growth (elongation) and binary fission of bacilli. Blue and red lines indicate old and newly generated bacterial cell wall, respectively. (1) growth at the centre of the bacterial body. e.g. Bacillus subtilis, E. coli, and others. (2) apical growth. e.g. Corynebacterium diphtheriae. This is bacterial proliferation. Bacilli division diagram.svg
Schematic diagram of cellular growth (elongation) and binary fission of bacilli. Blue and red lines indicate old and newly generated bacterial cell wall, respectively. (1) growth at the centre of the bacterial body. e.g. Bacillus subtilis , E. coli , and others. (2) apical growth. e.g. Corynebacterium diphtheriae . This is bacterial proliferation.

Organisms in the domains of Archaea and Bacteria reproduce with binary fission. This form of asexual reproduction and cell division is also used by some organelles within eukaryotic organisms (e.g., mitochondria). Binary fission results in the reproduction of a living prokaryotic cell (or organelle) by dividing the cell into two parts, each with the potential to grow to the size of the original.

Fission of prokaryotes

The single DNA molecule first replicates, then attaches each copy to a different part of the cell membrane. When the cell begins to pull apart, the replicated and original chromosomes are separated. The consequence of this asexual method of reproduction is that all the cells are genetically identical, meaning that they have the same genetic material (barring random mutations). Unlike the processes of mitosis and meiosis used by eukaryotic cells, binary fission takes place without the formation of a spindle apparatus on the cell. Like in mitosis (and unlike in meiosis), the parental identity is lost.

Process of FtsZ-dependent fission

Binary fission in a prokaryote Binary Fission 2.svg
Binary fission in a prokaryote

FtsZ is homologous to β-tubulin, the building block of the microtubule cytoskeleton used during mitosis in eukaryotes. [4] FtsZ is thought to be the first protein to localize to the site of future division in bacteria, and it assembles into a Z ring, anchored by FtsZ-binding proteins and defines the division plane between the two daughter cells. [5] [4] MinC and MinD function together as division inhibitors, blocking formation of the FtsZ ring. MinE stops the MinCD activity midcell, allowing FtsZ to take over for binary fission. [6]

More specifically, the following steps occur:

  1. The bacterium before binary fission is when the DNA is tightly coiled.
  2. The DNA of the bacterium has uncoiled and duplicated.
  3. The DNA is pulled to the separate poles of the bacterium as it increases the size to prepare for splitting.
  4. The growth of a new cell wall begins to separate the bacterium (triggered by FtsZ polymerization and "Z-ring" formation) [7]
  5. The new cell wall (septum) fully develops, resulting in the complete split of the bacterium.
  6. The new daughter cells have tightly coiled DNA rods, ribosomes, and plasmids; these are now brand-new organisms.

Studies of bacteria made to not produce a cell wall, called L-form bacteria, shows that FtsZ requires a cell wall to work. Little is known about how bacteria that naturally don't grow a cell wall divides, but it is thought to resemble the L-form's budding-like division process of extrusion and separation. [8] [9]

Speed of FtsZ-dependent Fission

Binary fission is generally rapid though its speed varies between species. For E. coli , cells typically divide about every 20 minutes at 37 °C. [10] Because the new cells will, in turn, undergo binary fission on their own, the time binary fission requires is also the time the bacterial culture requires to double in the number of cells it contains. This time period can, therefore, be referred to as the doubling time. Some species other than E. coli may have faster or slower doubling times: some strains of Mycobacterium tuberculosis may have doubling times of nearly 100 hours. [11] Bacterial growth is limited by factors including nutrient availability and available space, so binary fission occurs at much lower rates in bacterial cultures once they enter the stationary phase of growth.

In archaea

Crenarchaeota possess neither a cell wall nor the FtsZ mechanism. They use a primitive version of the eukaryotic ESCRT-III system (also known as Cdv) to manipulate the membrane into separating, specifically by coming into the middle of the two soon-to-be daughter cells. [12] [9] Euryarchaeota use FtsZ like bacteria do. [4] [13]

Fission of organelles

Some organelles in eukaryotic cells reproduce using binary fission. Mitochondrial fission occurs frequently within the cell, even when the cell is not actively undergoing mitosis, and is necessary to regulate the cell's metabolism. [14] All chloroplasts and some mitochrondria (not in animals), both organelles derived from endosymbiosis of bacteria, also use FtsZ in a bacteria-like fashion. [4] [15]

Types of binary fission

Binary fission in organisms can occur in four ways, irregular, longitudinal, transverse, oblique.i.e.left oblique & right oblique

  1. Irregular: In this fission, cytokinesis may take place along any plane but it is always perpendicular to the plane of karyokinesis (nuclear division). e.g. amoeba
  2. Longitudinal: Here cytokinesis takes place along the longitudinal axis. e.g. in flagellates like Euglena .
  3. Transverse: Here cytokinesis takes place along the transverse axis. e.g. in ciliate protozoans like Paramecium .
  4. Oblique: In this type of binary fission cytokinesis occurs obliquely. Example Ceratium

Binary fission means "division into two". It is the simplest and most common method of asexual reproduction.

Multiple fission

Fission of protists

Multiple fission at the cellular level occurs in many protistists, e.g. sporozoans and algae. The nucleus of the parent cell divides several times by amitosis, producing several nuclei. The cytoplasm then separates, creating multiple daughter cells. [16] [17] [18]

Some parasitic, single-celled organisms undergo a multiple fission-like process to produce numerous daughter cells from a single parent cell. Isolates of the human parasite Blastocystis hominis were observed to begin such a process within 4 to 6 days. [19] Cells of the fish parasite Trypanosoma borreli have also been observed participating in both binary and multiple fission. [20]

Fission of apicomplexans

In the apicomplexans, a phylum of parasitic protists, multiple fission, or schizogony, is manifested either as merogony, sporogony or gametogony. Merogony results in merozoites, which are multiple daughter cells, that originate within the same cell membrane, [21] [22] sporogony results in sporozoites, and gametogony results in microgametes.

Fission of green algae

Green algae can divide into more than two daughter cells. The exact number of daughter cells depends on the species of algae and is an effect of temperature and light. [23]

Multiple fission of bacteria

Most species of bacteria primarily undergo binary reproduction. Some species and groups of bacteria may undergo multiple fission as well, sometimes beginning or ending with the production of spores. [24] The species Metabacterium polyspora , a symbiont of guinea pigs, has been found to produce multiple endospores in each division. [25] Some species of cyanobacteria have also been found to reproduce through multiple fission. [26]

Plasmotomy

Some protozoans reproduce by yet another mechanism of fission called as plasmotomy. In this type of fission, a multinucleate adult parent undergoes cytokinesis to form two multinucleate (or coenocytic) daughter cells. The daughter cells so produced undergo further mitosis.

Opalina and Pelomyxa reproduce in this way.

Clonal fragmentation

Fragmentation in multicellular or colonial organisms is a form of asexual reproduction or cloning, where an organism is split into fragments. Each of these fragments develop into mature, fully grown individuals that are clones of the original organism. In echinoderms, this method of reproduction is usually known as fissiparity. [27]

Population fission

Any splitting of a single population of individuals into discrete parts may be considered fission. A population may undergo fission process for a variety of reasons, including migration or geographic isolation. Since the fission leads to genetic variance in the newly isolated, smaller populations, population fission is a precursor to speciation. [28] [29]

See also

Related Research Articles

Asexual reproduction Reproduction without a sexual process

Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the full set of genes of their single parent. Asexual reproduction is the primary form of reproduction for single-celled organisms such as archaea and bacteria. Many eukaryotic organisms including plants, animals, and fungi can also reproduce asexually. In vertebrates, the most common form of asexual reproduction is parthenogenesis, which is typically used as an alternative to sexual reproduction in times when reproductive opportunities are limited.

Cell (biology) Basic unit of all known organisms

The cell is the basic structural, functional, and biological unit of all known organisms. A cell is the smallest unit of life. Therefore, cells are often described as the "building blocks of life". Cell biology is the study of cells.

Cell biology is a branch of biology that studies the structure, function and behavior of cells. Cell biology encompasses both prokaryotic and eukaryotic cells and can be divided into many sub-topics which may include the study of cell metabolism, cell communication, cell cycle, biochemistry, and cell composition. The study of cells is performed using several techniques such as cell culture, various types of microscopy, and cell fractionation. These have allowed for and are currently being used for discoveries and research pertaining to how cells function, ultimately giving insight into understanding larger organisms. Knowing the components of cells and how cells work is fundamental to all biological sciences while also being essential for research in biomedical fields such as cancer, and other diseases. Research in cell biology is interconnected to other fields such as genetics, molecular genetics, biochemistry, molecular biology, medical microbiology, immunology, and cytochemistry.

Mitosis Part of the cell cycle

In cell biology, mitosis is a part of the cell cycle in which replicated chromosomes 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 is preceded by the S stage of interphase 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.

Cell division The process resulting in division and partitioning of components of a cell to form more cells; may or may not be accompanied by the physical separation of a cell into distinct, individually membrane-bounded daughter cells.

Cell division is the process by which a parent cell divides into two or more daughter cells. Cell division usually occurs as part of a larger cell cycle. In eukaryotes, there are two distinct types of cell division; a vegetative division, whereby each daughter cell is genetically identical to the parent cell (mitosis), and a reproductive cell division, whereby the number of chromosomes in the daughter cells is reduced by half to produce haploid gametes (meiosis). In cell biology, mitosis (/maɪˈtoʊsɪs/) is a part of the cell cycle, in which, replicated chromosomes are separated into two new nuclei. Cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. In general, mitosis is preceded by the S stage of interphase 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 all together define the mitotic (M) phase of an animal cell cycle—the division of the mother cell into two genetically identical daughter cells. Meiosis results in four haploid daughter cells by undergoing one round of DNA replication followed by two divisions. Homologous chromosomes are separated in the first division, and sister chromatids are separated in the second division. Both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. Both are believed to be present in the last eukaryotic common ancestor.

Cytoskeleton Network of filamentous proteins that forms the internal framework of cells

The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including bacteria and archaea. It extends from the cell nucleus to the cell membrane and is composed of similar proteins in the various organisms. In eukaryotes, it is composed of three main components, microfilaments, intermediate filaments and microtubules, and these are all capable of rapid growth or disassembly dependent on the cell's requirements.

<i>Paramecium</i> Genus of unicellular ciliates, commonly studied as a representative of the ciliate group

Paramecium is a genus of eukaryotic, unicellular ciliates, commonly studied as a representative of the ciliate group. Paramecia are widespread in freshwater, brackish, and marine environments and are often very abundant in stagnant basins and ponds. Because some species are readily cultivated and easily induced to conjugate and divide, it has been widely used in classrooms and laboratories to study biological processes. Its usefulness as a model organism has caused one ciliate researcher to characterize it as the "white rat" of the phylum Ciliophora.

Unicellular organism Organism that consists of only one cell

A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Unicellular organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms. All prokaryotes are unicellular and are classified into bacteria and archaea. Many eukaryotes are multicellular, but many are unicellular such as protozoa, unicellular algae, and unicellular fungi. Unicellular organisms are thought to be the oldest form of life, with early protocells possibly emerging 3.8–4.0 billion years ago.

Biological life cycle Life cycle of living species

In biology, a biological life cycle is a series of changes in form that an organism undergoes, returning to the starting state. "The concept is closely related to those of the life history, development and ontogeny, but differs from them in stressing renewal." Transitions of form may involve growth, asexual reproduction, or sexual reproduction.

FtsZ

FtsZ is a protein encoded by the ftsZ gene that assembles into a ring at the future site of bacterial cell division. FtsZ is a prokaryotic homologue of the eukaryotic protein tubulin. The initials FtsZ mean "Filamenting temperature-sensitive mutant Z." The hypothesis was that cell division mutants of E. coli would grow as filaments due to the inability of the daughter cells to separate from one another. FtsZ is found in almost all bacteria, many archaea, all chloroplasts and some mitochondria, where it is essential for cell division. FtsZ assembles the cytoskeletal scaffold of the Z ring that, along with additional proteins, constricts to divide the cell in two.

Cell growth

Cell growth refers to an increase in the total mass of a cell, including both cytoplasmic, nuclear and organelle volume. Cell growth occurs when the overall rate of cellular biosynthesis is greater than the overall rate of cellular degradation.

Planctomycetes Phylum of aquatic bacteria

The Planctomycetes are a phylum of widely distributed bacteria, occurring in both aquatic and terrestrial habitats. They play a considerable role in global carbon and nitrogen cycles, with many species of this phylum capable of anaerobic ammonium oxidation, also known as anammox. Many planctomycetes occur in relatively high abundance as biofilms, often associating with other organisms such as macroalgae and marine sponges.

Epulopiscium spp. are a group of Gram-positive bacteria that have a symbiotic relationship with surgeonfish. These bacteria are known for their unusually large size, many ranging from 200–700 μm in length. Until the discovery of Thiomargarita namibiensis in 1999, Epulopiscium spp. were thought to be the largest bacteria. They are still the largest known heterotrophic bacteria.

Viral eukaryogenesis is the hypothesis that the cell nucleus of eukaryotic life forms evolved from a large DNA virus in a form of endosymbiosis within a methanogenic archaeon or a bacterium. The virus later evolved into the eukaryotic nucleus by acquiring genes from the host genome and eventually usurping its role. The hypothesis was proposed by Philip Bell in 2001 and was further popularized with the discovery of large, complex DNA viruses that are capable of protein biosynthesis. Recent supporting evidence includes the discovery that, upon the infection of a bacterial cell, the giant bacteriophage 201Phi2-1 assembles a nucleus-like structure that segregates proteins according to function. This nucleus-like structure and its key properties have been found conserved in the related phages.

Outline of cell biology Overview of and topical guide to cell biology

The following outline is provided as an overview of and topical guide to cell biology:

Prokaryote Unicellular organism that lacks a membrane-bound nucleus

A prokaryote is a typically unicellular organism that lacks a nuclear membrane-enclosed nucleus. The word prokaryote comes from the Greek πρό and κάρυον. In the two-empire system arising from the work of Édouard Chatton, prokaryotes were classified within the empire Prokaryota. But in the three-domain system, based upon molecular analysis, prokaryotes are divided into two domains: Bacteria and Archaea. Organisms with nuclei are placed in a third domain, Eukaryota. In the study of the origins of life, prokaryotes are thought to have arisen before eukaryotes.

Ciliate Taxon of protozoans with hair-like organelles called cilia

The ciliates are a group of protozoans characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but are in general shorter and present in much larger numbers, with a different undulating pattern than flagella. Cilia occur in all members of the group and are variously used in swimming, crawling, attachment, feeding, and sensation.

Eukaryote Domain of life having cells with nuclei

Eukaryotes are organisms whose cells have a nucleus enclosed within a nuclear envelope. Eukaryotes belong to the domain Eukaryota or Eukarya; their name comes from the Greek εὖ and κάρυον. The domain Eukaryota makes up one of the three domains of life; the prokaryotes – bacteria and archaea make up the other two domains. The eukaryotes are usually now regarded as having emerged in the Archaea or as a sister of the now cultivated Asgard archaea. Eukaryotes represent a tiny minority of the number of organisms; however, due to their generally much larger size, their collective global biomass is estimated to be about equal to that of prokaryotes. Eukaryotes emerged approximately 2.1–1.6 billion years ago, during the Proterozoic eon, likely as flagellated phagotrophs.

<i>Reticulomyxa</i> Genus of single-celled organisms

Reticulomyxa is a monospecific genus of freshwater foraminiferans. The type species is the unicellular Reticulomyxa filosa. It is found in freshwater environments as well as moist environments, like decomposing matter and damp soils. The heterotrophic naked foraminiferan can feed on microbes as well has larger organisms and is able to be sustained in culture by supplemented nutrients such as wheat germ and oats. The large, multinucleate foraminferan is characteristic for its lack of test and named for the network of connecting pseudopodia surrounding its central body mass. The organism has unique bidirectional cytoplasmic streaming throughout the anastomosing pseudopodia that is some of the fastest reported organelle transport observed. Reticulomyxa was first described in 1949 and is commonly used as a model organism for the unique transport of organelles throughout the cytoplasm of pseudopodia by cytoskeletal mechanisms. Only asexual reproduction of this genus has been observed in culture, but the genome possesses genes related to meiosis suggesting it is capable of sexually reproductive life stages.

Divisome The divisome is a protein complex in bacteria that is responsible for cell division

The divisome is a protein complex in bacteria that is responsible for cell division, constriction of inner and outer membranes during division, and peptidoglycan (PG) synthesis at the division site. The divisome is a membrane protein complex with proteins on both sides of the cytoplasmic membrane. In gram-negative cells it is located in the inner membrane. The divisome is nearly ubiquitous in bacteria although its composition may vary between species.

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