Eukaryote

Edit links
This is a good article. Click here for more information.
Source: Wikipedia, the free encyclopedia.

"Eukaryotic cell" redirects here. For the journal, see Eukaryotic Cell (journal).

Eukaryota
Temporal range: Statherian–Present 1650–0 Ma
Discoba
Scientific classification Edit this classification
Domain: Eukaryota
(Chatton, 1925) Whittaker & Margulis, 1978
Subgroups
Synonyms

The eukaryotes (

global biomass
is much larger than that of prokaryotes.

The eukaryotes seemingly emerged within the

proteobacterium, which formed the mitochondria. A second episode of symbiogenesis with a cyanobacterium created the plants, with chloroplasts
.

Eukaryotic cells contain

fertilization
).

Etymology

The word 'Eukaryote' is derived from the Greek words "eu" (εὖ) meaning "true" or "good" and "karyon" (κάρυον) meaning "nut" or "kernel," referring to the nucleus of a cell.[6]

Diversity

Further information: Organism

Eukaryotes are organisms that range from microscopic single cells, such as picozoans under 3 micrometres across,[7] to animals like the blue whale, weighing up to 190 tonnes and measuring up to 33.6 metres (110 ft) long,[8] or plants like the coast redwood, up to 120 metres (390 ft) tall.[9] Many eukaryotes are unicellular; the informal grouping called protists includes many of these, with some multicellular forms like the giant kelp up to 200 feet (61 m) long.[10] The multicellular eukaryotes include the animals, plants, and fungi, but again, these groups too contain many unicellular species.[11] Eukaryotic cells are typically much larger than those of prokaryotes—the bacteria and the archaea—having a volume of around 10,000 times greater.[12][13] Eukaryotes represent a small minority of the number of organisms, but, as many of them are much larger, their collective global biomass (468 gigatons) is far larger than that of prokaryotes (77 gigatons), with plants alone accounting for over 81% of the total biomass of Earth.[14]

The eukaryotes are a diverse lineage, consisting mainly of

land plants.[18] Eukaryotes are grouped by genomic similarities, so that groups often lack visible shared characteristics.[15]

Distinguishing features

Further information: Cell (biology) § Eukaryotic cells

Nucleus

The defining feature of eukaryotes is that

nuclei, distinguishing them from prokaryotes that lack such a structure. Eukaryotic cells have a variety of internal membrane-bound structures, called organelles, and a cytoskeleton which defines the cell's organization and shape. The nucleus stores the cell's DNA, which is divided into linear bundles called chromosomes;[19] these are separated into two matching sets by a microtubular spindle during nuclear division, in the distinctively eukaryotic process of mitosis.[20]

Biochemistry

Eukaryotes differ from prokaryotes in multiple ways, with unique biochemical pathways such as

nuclear pore, and some enzymes in the biochemical pathways.[22]

Internal membranes

Further information: Endomembrane system
membrane-bound organelles
.

Eukaryote cells include a variety of membrane-bound structures, together forming the endomembrane system.

vesicles and vacuoles, can form by budding off other membranes. Many cells ingest food and other materials through a process of endocytosis, where the outer membrane invaginates and then pinches off to form a vesicle.[24] Some cell products can leave in a vesicle through exocytosis.[25]

The nucleus is surrounded by a double membrane known as the

protein transport and maturation. It includes the rough endoplasmic reticulum, covered in ribosomes which synthesize proteins; these enter the interior space or lumen. Subsequently, they generally enter vesicles, which bud off from the smooth endoplasmic reticulum.[27] In most eukaryotes, these protein-carrying vesicles are released and further modified in stacks of flattened vesicles (cisternae), the Golgi apparatus.[28]

Vesicles may be specialized; for instance, lysosomes contain digestive enzymes that break down biomolecules in the cytoplasm.[29]

Mitochondria

Main article: Mitochondrion
Mitochondria are essentially universal in the eukaryotes, and with their own DNA somewhat resemble prokaryotic cells.

Mitochondria are organelles in eukaryotic cells. The mitochondrion is commonly called "the powerhouse of the cell",

aerobic respiration takes place.[33]

Mitochondria contain

tRNA genes that produce RNA which is closer in structure to bacterial RNA than to eukaryote RNA.[34]

Some eukaryotes, such as the metamonads Giardia and Trichomonas, and the amoebozoan Pelomyxa, appear to lack mitochondria, but all contain mitochondrion-derived organelles, like hydrogenosomes or mitosomes, having lost their mitochondria secondarily.[35] They obtain energy by enzymatic action in the cytoplasm.[36][35] It is thought that mitochondria developed from prokaryotic cells which became endosymbionts living inside eukaryotes.[37]

Plastids

Main article: Plastid
The most common type of plastid is the chloroplast, which contains chlorophyll and produces organic compounds by photosynthesis.

Plants and various groups of

secondary endosymbiosis or ingestion.[38] The capture and sequestering of photosynthetic cells and chloroplasts, kleptoplasty, occurs in many types of modern eukaryotic organisms.[39][40]

Cytoskeletal structures

Main article: Cytoskeleton
microtubules
in green. (The nucleus is in blue.)

The cytoskeleton provides stiffening structure and points of attachment for motor structures that enable the cell to move, change shape, or transport materials. The motor structures are microfilaments of actin and actin-binding proteins, including α-actinin, fimbrin, and filamin are present in submembranous cortical layers and bundles. Motor proteins of microtubules, dynein and kinesin, and myosin of actin filaments, provide dynamic character of the network.[41][42]

Many eukaryotes have long slender motile cytoplasmic projections, called flagella, or multiple shorter structures called cilia. These organelles are variously involved in movement, feeding, and sensation. They are composed mainly of tubulin, and are entirely distinct from prokaryotic flagella. They are supported by a bundle of microtubules arising from a centriole, characteristically arranged as nine doublets surrounding two singlets. Flagella may have hairs (mastigonemes), as in many stramenopiles. Their interior is continuous with the cell's cytoplasm.[43][44]

Centrioles are often present, even in cells and groups that do not have flagella, but conifers and flowering plants have neither. They generally occur in groups that give rise to various microtubular roots. These form a primary component of the cytoskeleton, and are often assembled over the course of several cell divisions, with one flagellum retained from the parent and the other derived from it. Centrioles produce the spindle during nuclear division.[45]

Cell wall

Main article: Cell wall

The cells of plants, algae, fungi and most chromalveolates, but not animals, are surrounded by a cell wall. This is a layer outside the cell membrane, providing the cell with structural support, protection, and a filtering mechanism. The cell wall also prevents over-expansion when water enters the cell.[46]

The major

land plants are cellulose, hemicellulose, and pectin. The cellulose microfibrils are linked together with hemicellulose, embedded in a pectin matrix. The most common hemicellulose in the primary cell wall is xyloglucan.[47]

Sexual reproduction

Further information: Evolution of sexual reproduction
diploid phase, with two copies. In eukaryotes, haploid gametes are produced by meiosis; two gametes fuse to form a diploid zygote
.

Eukaryotes have a life cycle that involves

spermatozoa, to form a zygote; this may grow into a body, with its cells dividing by mitosis, and at some stage produce haploid gametes through meiosis, a division that reduces the number of chromosomes and creates genetic variability.[48] There is considerable variation in this pattern. Plants have both haploid and diploid multicellular phases.[49] Eukaryotes have lower metabolic rates and longer generation times than prokaryotes, because they are larger and therefore have a smaller surface area to volume ratio.[50]

The

Giardia intestinalis, two organisms previously thought to be asexual.[52][53] Since these two species are descendants of lineages that diverged early from the eukaryotic evolutionary tree, core meiotic genes, and hence sex, were likely present in the common ancestor of eukaryotes.[52][53] Species once thought to be asexual, such as Leishmania parasites, have a sexual cycle.[54] Amoebae, previously regarded as asexual, may be anciently sexual; while present-day asexual groups could have arisen recently.[55]

Evolution

History of classification

Further information:
History of taxonomy

In

Protista, in 1866.[58][59][60]
The eukaryotes thus came to be seen as four kingdoms:

  • Kingdom
    Protista
  • Kingdom
    Plantae
  • Kingdom
    Fungi
  • Kingdom
    Animalia

The protists were at that time thought to be "primitive forms", and thus an evolutionary grade, united by their primitive unicellular nature.[59] Understanding of the oldest branchings in the tree of life only developed substantially with DNA sequencing, leading to a system of domains rather than kingdoms as top level rank being put forward by Carl Woese, Otto Kandler, and Mark Wheelis in 1990, uniting all the eukaryote kingdoms in the domain "Eucarya", stating, however, that "'eukaryotes' will continue to be an acceptable common synonym".[2][61] In 1996, the evolutionary biologist Lynn Margulis proposed to replace kingdoms and domains with "inclusive" names to create a "symbiosis-based phylogeny", giving the description "Eukarya (symbiosis-derived nucleated organisms)".[3]

Phylogeny

Tree of eukaryotes showing major subgroups and thumbnail diagrams of representative members of each group, based on 2023 phylogenomic reconstructions.[62]

By 2014, a rough consensus started to emerge from the phylogenomic studies of the previous two decades.

Discoba),[65] and incorporates the 2021 proposal that picozoans are close relatives of rhodophytes.[66] The Provora are a group of microbial predators discovered in 2022.[1]


Eukaryotes

Ancyromonadida

Malawimonada

CRuMs

Amorphea

Amoebozoa

Obazoa

Breviatea

Apusomonadida

Opisthokonta

Holomycota (inc. fungi)

Holozoa (inc. animals)

1300 mya
1500 mya
Diphoda

?

Metamonada

Discoba

Diaphoretickes

Cryptista

Archaeplastida

Rhodophyta (red algae)

Picozoa

Glaucophyta

1100 mya

Viridiplantae (plants)

1000 mya
1600 mya

Hemimastigophora

Provora

Haptista

TSAR

Telonemia

SAR

Rhizaria

550 mya
Halvaria

Alveolata

Stramenopiles

Bikonts
2200 mya

One view of the great kingdoms and their stem groups.

Malawimonada[15] or being a paraphyletic group external to all other eukaryotes.[69]

Origin of eukaryotes

Main article: Eukaryogenesis
In the theory of symbiogenesis, a merger of an archaean and an aerobic bacterium created the eukaryotes, with aerobic mitochondria; a second merger added chloroplasts, creating the green plants.[70]

The origin of the eukaryotic cell, or eukaryogenesis, is a milestone in the evolution of life, since eukaryotes include all complex cells and almost all multicellular organisms. The

syngamy), a dormant cyst with a cell wall of chitin or cellulose, and peroxisomes.[73][74][75]

An endosymbiotic union between a motile anaerobic archaean and an aerobic alphaproteobacterium gave rise to the LECA and all eukaryotes, with mitochondria. A second, much later endosymbiosis with a cyanobacterium gave rise to the ancestor of plants, with chloroplasts.[70]

The presence of eukaryotic biomarkers in archaea points towards an archaeal origin. The genomes of

cryo-electron tomography demonstrated that Asgard archaea have a complex actin-based cytoskeleton, providing the first direct visual evidence of the archaeal ancestry of eukaryotes.[76]

Fossils

The timing of the origin of eukaryotes is hard to determine, but the discovery of Qingshania magnificia, the earliest multicelluar eukaryote from North China which lived 1.635 billion years ago, suggests that the crown group eukaryotes originated from the late Paleoproterozoic (Statherian). The earliest unequivocal unicellular eukaryotes, Tappania plana, Shuiyousphaeridium macroreticulatum, Dictyosphaera macroreticulata, Germinosphaera alveolata, and Valeria lophostriata from North China, lived approximately 1.65 billion years ago.[77]

Some acritarchs are known from at least 1.65 billion years ago, and a fossil, Grypania, which may be an alga, is as much as 2.1 billion years old.[78][79] The "problematic"[80] fossil Diskagma has been found in paleosols 2.2 billion years old.[80]

Diskagma buttonii
, a terrestrial fossil less than 1mm high, from rocks around 2.2 billion years old

The Neoarchean fossil Thuchomyces shares similarities with eukaryotes, specifically fungi. It especially resembles the problematic fossil Diskagma,[80] with hyphae and multiple differentiated layers.[81] However, it is over 600 million years older than all other possible eukaryotes, and many of its "eukaryote features" are not specific to the clade, meaning it is almost certainly a microbial mat instead.[82]

Structures proposed to represent "large colonial organisms" have been found in the

Vindhya basin dating back perhaps to 1.6 to 1.7 billion years ago.[87]

The presence of

biomarkers, in Australian shales previously indicated that eukaryotes were present in these rocks dated at 2.7 billion years old,[21][88] but these Archaean biomarkers have been rebutted as later contaminants.[89] The oldest valid biomarker records are only around 800 million years old.[90] In contrast, a molecular clock analysis suggests the emergence of sterol biosynthesis as early as 2.3 billion years ago.[91] The nature of steranes as eukaryotic biomarkers is further complicated by the production of sterols by some bacteria.[92][93]

Whenever their origins, eukaryotes may not have become ecologically dominant until much later; a massive increase in the zinc composition of marine sediments 800 million years ago has been attributed to the rise of substantial populations of eukaryotes, which preferentially consume and incorporate zinc relative to prokaryotes, approximately a billion years after their origin (at the latest).[94]

See also

References

  1. ^
    S2CID 254436650
    .
  2. ^
    PMID 2112744
    .
  3. ^
    PMID 8577716
    .
  4. ^ "eukaryote". Merriam-Webster.com Dictionary. Merriam-Webster.
  5. PMID 37316666
    .
  6. ^ "eukaryotic (adj.)". Online Etymology Dictionary. Retrieved 7 January 2025.
  7. PMID 23555709
    .
  8. ISBN 978-0-85112-235-9
    .
  9. ^ Earle CJ, ed. (2017). "Sequoia sempervirens". The Gymnosperm Database. Archived from the original on 1 April 2016. Retrieved 15 September 2017.
  10. ISBN 0-521-30419-9. Archived
    from the original on 10 February 2023. Retrieved 7 April 2023.
  11. ^
    PMID 24789819
    .
  12. ISBN 9780123847201
    .
  13. ^ Yamaguchi M, Worman CO (2014). "Deep-sea microorganisms and the origin of the eukaryotic cell" (PDF). Japanese Journal of Protozoology. 47 (1, 2): 29–48. Archived from the original (PDF) on 9 August 2017.
  14. PMID 29784790
    .
  15. ^
    S2CID 204545629
    .
  16. doi:10.1146/annurev.ecolsys.36.102403.114735. Archived
    (PDF) from the original on 14 March 2023. Retrieved 8 April 2023.
  17. S2CID 13872783. Archived
    (PDF) from the original on 25 July 2014. Retrieved 8 April 2023.
  18. S2CID 11961888
    .
  19. S2CID 31259189
    .
  20. ^ O'Connor, Clare (2008). "Chromosome Segregation: The Role of Centromeres". Nature Education. Retrieved 18 February 2024. eukar
  21. ^
    PMID 10446042
    .
  22. PMID 11805300
    .
  23. ISBN 978-94-007-1533-2. Archived
    from the original on 29 May 2016. Retrieved 27 October 2015.
  24. ISBN 978-0-19-963851-2
    .
  25. PMID 32317144
    .
  26. PMID 20300205
    .
  27. ^ "Endoplasmic Reticulum (Rough and Smooth)". British Society for Cell Biology. Archived from the original on 24 March 2019. Retrieved 12 November 2017.
  28. ^ "Golgi Apparatus". British Society for Cell Biology. Archived from the original on 13 November 2017. Retrieved 12 November 2017.
  29. ^ "Lysosome". British Society for Cell Biology. Archived from the original on 13 November 2017. Retrieved 12 November 2017.
  30. PMID 32166015
    .
  31. ISBN 978-0471214953
    .
  32. ^ Mack S (1 May 2006). "Re: Are there eukaryotic cells without mitochondria?". madsci.org. Archived from the original on 24 April 2014. Retrieved 24 April 2014.
  33. PMID 18620004
    .
  34. ISBN 978-0-8053-9614-0
    .
  35. ^
    PMID 27185558
    .
  36. ^ Davis JL (13 May 2016). "Scientists Shocked To Discover Eukaryote With NO Mitochondria". IFL Science. Archived from the original on 17 February 2019. Retrieved 13 May 2016.
  37. PMID 34242059
    .
  38. ISBN 978-1-4020-4060-3
    .
  39. PMID 18518896
    .
  40. S2CID 24613863
    .
  41. ISBN 978-0-8153-3218-3. Archived
    from the original on 8 March 2019. Retrieved 6 April 2023.
  42. PMID 29716949
    .
  43. PMID 12624192
    .
  44. PMID 11743094
    .
  45. PMID 3294718
    .
  46. ISBN 978-0-19-511183-5
    .
  47. doi:10.1093/jxb/40.1.1
    .
  48. ISBN 978-1-4051-3277-0
    .
  49. PMID 15809414
    .
  50. PMID 21714941
    .
  51. S2CID 9441768
    .
  52. ^
    S2CID 17013247
    .
  53. ^
    PMID 18663385
    .
  54. PMID 19359589
    .
  55. PMID 21429931
    .
  56. doi:10.1515/bot-1980-230605
    .
  57. ^ Goldfuß (1818). "Ueber die Classification der Zoophyten" [On the classification of zoophytes]. Isis, Oder, Encyclopädische Zeitung von Oken (in German). 2 (6): 1008–1019. Archived from the original on 24 March 2019. Retrieved 15 March 2019. From p. 1008: "Erste Klasse. Urthiere. Protozoa." (First class. Primordial animals. Protozoa.) [Note: each column of each page of this journal is numbered; there are two columns per page.]
  58. PMID 10943416. Archived from the original
    (PDF) on 14 June 2011.
  59. ^
    S2CID 32462158. Archived
    from the original on 4 February 2020. Retrieved 4 February 2020.
  60. PMID 5762760
    .
  61. PMID 1585174
    . Eucarya, or eukaryotes
  62. Wikidata Q123558544
    .
  63. PMID 26817772
    .
  64. PMID 30257078
    .
  65. ^
    PMID 29360967
    .
  66. S2CID 233328713. Archived
    from the original on 2 February 2024. Retrieved 20 December 2021.
  67. S2CID 233328713
    .
  68. S2CID 254436650
    .
  69. PMID 37115919
    .
  70. ^
    ISBN 978-0-521-76131-4. Archived
    from the original on 24 March 2019. Retrieved 27 August 2017.
  71. S2CID 236916203
    .
  72. S2CID 67790751
    .
  73. S2CID 218710816
    .
  74. PMID 33767194
    .
  75. PMID 23895660
    .
  76. PMID 36544020
    .
  77. PMID 38266082
    .
  78. PMID 1631544
    .
  79. PMID 16754612
    .
  80. ^
    doi:10.1016/j.precamres.2013.05.015
    .
  81. doi:10.1007/BF01989590
    .
  82. doi:10.1016/B978-0-12-813012-4.00023-1
    .
  83. S2CID 4331375
    .
  84. S2CID 258360867
    .
  85. doi:10.1016/j.epsl.2023.118147
    .
  86. S2CID 257761993
    .
  87. PMID 19416859
    .
  88. ^ Ward P (9 February 2008). "Mass extinctions: the microbes strike back". New Scientist. pp. 40–43. Archived from the original on 8 July 2008. Retrieved 27 August 2017.
  89. PMID 25918387
    .
  90. S2CID 205258987
    .
  91. S2CID 205254122
    .
  92. PMID 27446030
    .
  93. PMID 34131078
    .
  94. PMID 29869832
    .
Wikispecies has information related to Eukaryota.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Eukaryote&oldid=1268659921"