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Evolution of cells

August 23, 2023

See also: Abiogenesis and Protocell
"Cytogenesis" redirects here. Not to be confused with Citogenesis.

Evolution of cells refers to the evolutionary origin and subsequent evolutionary development of cells. Cells first emerged at least 3.8 billion years ago[1][2][3] approximately 750 million years after Earth was formed.[4]

The first cells

Main articles: Abiogenesis and Earliest known life forms

The initial development of the cell marked the passage from prebiotic chemistry to partitioned units resembling modern cells. The final transition to living entities that fulfill all the definitions of modern cells depended on the ability to evolve effectively by natural selection. This transition has been called the Darwinian transition.

If life is viewed from the point of view of replicator molecules, cells satisfy two fundamental conditions: protection from the outside environment and confinement of biochemical activity. The former condition is needed to keep complex molecules stable in a varying and sometimes aggressive environment; the latter is fundamental for the evolution of biocomplexity. If freely floating molecules that code for enzymes are not enclosed in cells, the enzymes will automatically benefit neighboring replicator molecules as well. Thus, the consequences of diffusion in non-partitioned lifeforms would result in "parasitism by default." Therefore, the selection pressure on replicator molecules will be lower, as the 'lucky' molecule that produces the better enzyme does not fully leverage its advantage over its close neighbors. In contrast, if the molecule is enclosed in a cell membrane, the enzymes coded will be available only to itself. That molecule will uniquely benefit from the enzymes it codes for, increasing individuality and thus accelerating natural selection.

Partitioning may have begun from cell-like spheroids formed by proteinoids, which are observed by heating amino acids with phosphoric acid as a catalyst. They bear much of the basic features provided by cell membranes. Proteinoid-based protocells enclosing RNA molecules could have been the first cellular life forms on Earth.[5]

Another possibility is that the shores of the ancient coastal waters may have been a suitable environment for the initial development of cells. Waves breaking on the shore create a delicate foam composed of bubbles. Shallow coastal waters also tend to be warmer, further concentrating the molecules through evaporation. While bubbles made mostly of water tend to burst quickly, oily bubbles are much more stable. The phospholipid, the primary material of cell membranes, is an example of a common oily compound prevalent in the prebiotic seas.[6]

Both of these options require the presence of massive amounts of chemicals and organic material in order to form cells. A large gathering of organic molecules most likely came from what scientists now call the prebiotic soup. The prebiotic soup refers to the collection of every organic compound that appeared on Earth after it was formed. This soup would have most likely contained the compounds necessary to form early cells.[7]

Phospholipids are composed of a hydrophilic head on one end and a hydrophobic tail on the other. They can come together to form a bilayer membrane. A lipid monolayer bubble can only contain oil and is not conducive to harboring water-soluble organic molecules. On the other hand, a lipid bilayer bubble can contain water and was a likely precursor to the modern cell membrane.[citation needed] If a protein was introduced that increased the integrity of its parent bubble, then that bubble had an advantage.[citation needed] Primitive reproduction may have occurred when the bubbles burst, releasing the results of the experiment into the surrounding medium. Once enough of the right compounds were released into the medium, the development of the first prokaryotes, eukaryotes, and multi-cellular organisms could be achieved.[8][citation needed]

However, the first cell membrane could not have been composed of phospholipids due its low permeability, as ions would not able to pass through the membrane. Rather it is suggested they were composed of fatty acids, as they can freely exchange ions, allowing geochemically sustained proton gradients at alkaline hydrothermal vents that might lead to prebiotic chemical reactions via CO2 fixation.[9]

Community metabolism

The common ancestor of the now existing cellular lineages (eukaryotes, bacteria, and archaea) may have been a community of organisms that readily exchanged components and genes. It would have contained:

  • Autotrophs that produced organic compounds from CO2, either photosynthetically or by inorganic chemical reactions;
  • Heterotrophs that obtained organics from leakage of other organisms
  • Saprotrophs that absorbed nutrients from decaying organisms
  • Phagotrophs that were sufficiently complex to envelop and digest particulate nutrients, including other organisms.

The eukaryotic cell seems to have evolved from a symbiotic community of prokaryotic cells. DNA-bearing organelles like mitochondria and chloroplasts are remnants of ancient symbiotic oxygen-breathing bacteria and cyanobacteria, respectively, where at least part of the rest of the cell may have been derived from an ancestral archaean prokaryote cell. The archean prokaryote cell concept is often termed as the endosymbiotic theory. There is still debate about whether organelles like the hydrogenosome predated the origin of mitochondria, or vice versa: see the hydrogen hypothesis for the origin of eukaryotic cells.

How the current lineages of microbes evolved from this postulated community is currently unsolved, but subject to intense research by biologists, stimulated by the great flow of new discoveries in genome science.[10]

Genetic code and the RNA world

Modern evidence suggests that early cellular evolution occurred in a biological realm radically distinct from modern biology. It is thought that in this ancient realm, the current genetic role of DNA was largely filled by RNA, and catalysis was also largely mediated by RNA (that is, by ribozyme counterparts of enzymes). This concept is known as the RNA world hypothesis.

According to this hypothesis, the ancient RNA world transitioned into the modern cellular world via the evolution of protein synthesis, followed by replacement of many cellular ribozyme catalysts by protein-based enzymes. Proteins are much more flexible in catalysis than RNA due to the existence of diverse amino acid side chains with distinct chemical characteristics. The RNA record in existing cells appears to preserve some 'molecular fossils' from this RNA world. These RNA fossils include the ribosome itself (in which RNA catalyzes peptide-bond formation), the modern ribozyme catalyst RNase P, and RNAs.[11][12][13][14]

The nearly universal genetic code preserves some evidence for the RNA world. For instance, recent studies of transfer RNAs, the enzymes that charge them with amino acids (the first step in protein synthesis) and the way these components recognize and exploit the genetic code, have been used to suggest that the universal genetic code emerged before the evolution of the modern amino acid activation method for protein synthesis.[11][12][15][16][17] The first RNA polymers probably emerged prior to 4.17 Gya if life originated at freshwater environments similar to Darwin's warm little pond.[18]

Sexual reproduction

The evolution of sexual reproduction may be a primordial and fundamental characteristic of eukaryotes, including single cell eukaryotes. Based on a phylogenetic analysis, Dacks and Roger[19] proposed that facultative sex was present in the common ancestor of all eukaryotes. Hofstatter and Lehr[20] reviewed evidence supporting the hypothesis that all eukaryotes can be regarded as sexual, unless proven otherwise.

Sexual reproduction may have arisen in early protocells with RNA genomes (RNA world).[21] Initially, each protocell would likely have contained one RNA genome (rather than multiple) since this maximizes the growth rate. However, the occurrence of damages to the RNA which block RNA replication or interfere with ribozyme function would make it advantageous to fuse periodically with another protocell to restore reproductive ability. This early, simple form of genetic recovery is similar to that occurring in extant segmented single-stranded RNA viruses (see influenza A virus).

As duplex DNA became the predominant form of the genetic material, the mechanism of genetic recovery evolved into the more complex process of meiotic recombination, found today in most species. It thus appears likely that sexual reproduction arose early in the evolution of cells and has had a continuous evolutionary history.

Horizontal gene transfer

Horizontal gene transfer (HGT) is the movement of genetic information between different organisms of the same species mainly being bacteria. This is not the movement of genetic information between a parent and their offspring but by other factors. In contrast to how animals reproduce and evolve from sexual reproduction, bacteria evolve by sharing DNA with other bacteria or their environment.

There are three common mechanisms of transferring genetic material by HGT:

Once one of these mechanisms has occurred the bacteria will continue to multiply and grow resistance and evolve by natural selection. HGT is the main cause of the assimilation of certain genetic material and the passing down of antibiotic resistance genes (ARGs).

Canonical patterns

Although the evolutionary origins of the major lineages of modern cells are disputed, the primary distinctions between the three major lineages of cellular life (called domains) are firmly established.

In each of these three domains, DNA replication, transcription, and translation all display distinctive features. There are three versions of ribosomal RNAs, and generally three versions of each ribosomal protein, one for each domain of life. These three versions of the protein synthesis apparatus are called the canonical patterns, and the existence of these canonical patterns provides the basis for a definition of the three domains - Bacteria, Archaea, and Eukarya (or Eukaryota) - of currently existing cells.[22]

Using genomics to infer early lines of evolution

Instead of relying a single gene such as the small-subunit ribosomal RNA (SSU rRNA) gene to reconstruct early evolution, or a few genes, scientific effort has shifted to analyzing complete genome sequences.[23]

Evolutionary trees based only on SSU rRNA alone do not capture the events of early eukaryote evolution accurately, and the progenitors of the first nucleated cells are still uncertain. For instance, analysis of the complete genome of the eukaryote yeast shows that many of its genes are more closely related to bacterial genes than they are to archaea, and it is now clear that archaea were not the simple progenitors of the eukaryotes, in contradiction to earlier findings based on SSU rRNA and limited samples of other genes.[24]

One hypothesis is that the first nucleated cell arose from two distinctly different ancient prokaryotic (non-nucleated) species that had formed a symbiotic relationship with one another to carry out different aspects of metabolism. One partner of this symbiosis is proposed to be a bacterial cell, and the other an archaeal cell. It is postulated that this symbiotic partnership progressed via the cellular fusion of the partners to generate a chimeric or hybrid cell with a membrane bound internal structure that was the forerunner of the nucleus. The next stage in this scheme was transfer of both partner genomes into the nucleus and their fusion with one another. Several variations of this hypothesis for the origin of nucleated cells have been suggested.[25] Other biologists dispute this conception[10] and emphasize the community metabolism theme, the idea that early living communities would comprise many different entities to extant cells, and would have shared their genetic material more extensively than current microbes.[26]

Quotes

"The First Cell arose in the previously prebiotic world with the coming together of several entities that gave a single vesicle the unique chance to carry out three essential and quite different life processes. These were: (a) to copy informational macromolecules, (b) to carry out specific catalytic functions, and (c) to couple energy from the environment into usable chemical forms. These would foster subsequent cellular evolution and metabolism. Each of these three essential processes probably originated and was lost many times prior to The First Cell, but only when these three occurred together was life jump-started and Darwinian evolution of organisms began." (Koch and Silver, 2005)[27]

"The evolution of modern cells is arguably the most challenging and important problem the field of Biology has ever faced. In Darwin's day the problem could hardly be imagined. For much of the 20th century it was intractable. In any case, the problem lay buried in the catch-all rubric "origin of life"--where, because it is a biological not a (bio)chemical problem, it was effectively ignored. Scientific interest in cellular evolution started to pick up once the universal phylogenetic tree, the framework within which the problem had to be addressed, was determined. But it was not until microbial genomics arrived on the scene that biologists could actually do much about the problem of cellular evolution." (Carl Woese, 2002) [28]

References

  1. ^ Schopf, JW, Kudryavtsev, AB, Czaja, AD, and Tripathi, AB. (2007). Evidence of Archean life: Stromatolites and microfossils. Precambrian Research 158:141-155.
  2. ^ Schopf, JW (2006). Fossil evidence of Archaean life. Philos Trans R Soc Lond B Biol Sci 29;361(1470):869-85.
  3. ^ Raven PH, Johnson GB (2002). Biology. McGraw-Hill Education. p. 68. ISBN 978-0-07-112261-0. Retrieved 7 July 2013.
  4. ^ Cooper GM (2000). "The Origin and Evolution of Cells". The Cell: A Molecular Approach (2nd ed.).
  5. ^ Fox SW, Dose K (1972). Molecular evolution and the origin of life. San Francisco: W.H. Freeman. ISBN 978-0-7167-0163-7. OCLC 759538.
  6. ^ "Big Picture". Big Picture. Retrieved 1 October 2019.
  7. ^ "The Prebiotic Soup". earthguide.ucsd.edu. Retrieved 1 October 2019.
  8. ^ This theory is expanded upon in The Cell: Evolution of the First Organism by Joseph Panno
  9. ^ Nunes Palmeira, Raquel; Colnaghi, Marco; Harrison, Stuart A.; Pomiankowski, Andrew; Lane, Nick (9 November 2022). "The limits of metabolic heredity in protocells". Proceedings of the Royal Society B: Biological Sciences. 289 (1986). doi:10.1098/rspb.2022.1469. ISSN 0962-8452. PMC 9653231. PMID 36350219.
  10. ^ a b Kurland CG, Collins LJ, Penny D (May 2006). "Genomics and the irreducible nature of eukaryote cells". Science. 312 (5776): 1011–1014. Bibcode:2006Sci...312.1011K. doi:10.1126/science.1121674. PMID 16709776. S2CID 30768101.
  11. ^ a b Poole AM, Jeffares DC, Penny D (January 1998). "The path from the RNA world". Journal of Molecular Evolution. 46 (1): 1–17. Bibcode:1998JMolE..46....1P. doi:10.1007/PL00006275. PMID 9419221. S2CID 17968659.
  12. ^ a b Jeffares DC, Poole AM, Penny D (January 1998). "Relics from the RNA world". Journal of Molecular Evolution. 46 (1): 18–36. Bibcode:1998JMolE..46...18J. doi:10.1007/PL00006280. PMID 9419222. S2CID 2029318.
  13. ^ Orgel LE (2004). "Prebiotic chemistry and the origin of the RNA world". Critical Reviews in Biochemistry and Molecular Biology. 39 (2): 99–123. CiteSeerX 10.1.1.537.7679. doi:10.1080/10409230490460765. PMID 15217990.
  14. ^ Benner SA, Ellington AD, Tauer A (September 1989). "Modern metabolism as a palimpsest of the RNA world". Proceedings of the National Academy of Sciences of the United States of America. 86 (18): 7054–7058. Bibcode:1989PNAS...86.7054B. doi:10.1073/pnas.86.18.7054. PMC 297992. PMID 2476811.
  15. ^ Hohn MJ, Park HS, O'Donoghue P, Schnitzbauer M, Söll D (November 2006). "Emergence of the universal genetic code imprinted in an RNA record". Proceedings of the National Academy of Sciences of the United States of America. 103 (48): 18095–18100. Bibcode:2006PNAS..10318095H. doi:10.1073/pnas.0608762103. PMC 1838712. PMID 17110438.
  16. ^ O'Donoghue P, Luthey-Schulten Z (December 2003). "On the evolution of structure in aminoacyl-tRNA synthetases". Microbiology and Molecular Biology Reviews. 67 (4): 550–573. doi:10.1128/MMBR.67.4.550-573.2003. PMC 309052. PMID 14665676.
  17. ^ Gesteland, RF et al. eds.(2006) The RNA World: The Nature of Modern RNA Suggests a Prebiotic RNA (2006) (Cold Spring Harbor Lab Press, Cold Spring Harbor, NY,).
  18. ^ Pearce BK, Pudritz RE, Semenov DA, Henning TK (October 2017). "Origin of the RNA world: The fate of nucleobases in warm little ponds". Proceedings of the National Academy of Sciences of the United States of America. 114 (43): 11327–11332. doi:10.1073/pnas.1710339114. PMC 5664528. PMID 28973920.
  19. ^ Dacks J, Roger AJ (June 1999). "The first sexual lineage and the relevance of facultative sex". Journal of Molecular Evolution. 48 (6): 779–783. Bibcode:1999JMolE..48..779D. doi:10.1007/PL00013156. PMID 10229582. S2CID 9441768
  20. ^ Hofstatter PG, Lahr DJG. All Eukaryotes Are Sexual, unless Proven Otherwise: Many So-Called Asexuals Present Meiotic Machinery and Might Be Able to Have Sex. Bioessays. 2019 Jun;41(6):e1800246. doi: 10.1002/bies.201800246. Epub 2019 May 14. PMID 31087693
  21. ^ Bernstein H, Byerly HC, Hopf FA, Michod RE. Origin of sex. J Theor Biol. 1984 Oct 5;110(3):323-51. doi: 10.1016/s0022-5193(84)80178-2. PMID 6209512
  22. ^ Olsen GJ, Woese CR (June 1997). "Archaeal genomics: an overview". Cell. 89 (7): 991–994. doi:10.1016/S0092-8674(00)80284-6. PMID 9215619. S2CID 7576095.
  23. ^ Daubin V, Moran NA, Ochman H (August 2003). "Phylogenetics and the cohesion of bacterial genomes". Science. 301 (5634): 829–832. Bibcode:2003Sci...301..829D. doi:10.1126/science.1086568. PMID 12907801. S2CID 11268678.
    • Eisen JA, Fraser CM (June 2003). "Phylogenomics: intersection of evolution and genomics". Science. 300 (5626): 1706–1707. Bibcode:2003Sci...300.1706E. doi:10.1126/science.1086292. PMID 12805538. S2CID 42394233.
    • Henz SR, Huson DH, Auch AF, Nieselt-Struwe K, Schuster SC (May 2005). "Whole-genome prokaryotic phylogeny". Bioinformatics. 21 (10): 2329–2335. doi:10.1093/bioinformatics/bth324. PMID 15166018.
  24. ^ Esser C, Ahmadinejad N, Wiegand C, Rotte C, Sebastiani F, Gelius-Dietrich G, et al. (September 2004). "A genome phylogeny for mitochondria among alpha-proteobacteria and a predominantly eubacterial ancestry of yeast nuclear genes". Molecular Biology and Evolution. 21 (9): 1643–1660. doi:10.1093/molbev/msh160. PMID 15155797.
  25. ^ Esser C, Ahmadinejad N, Wiegand C, Rotte C, Sebastiani F, Gelius-Dietrich G, et al. (September 2004). "A genome phylogeny for mitochondria among alpha-proteobacteria and a predominantly eubacterial ancestry of yeast nuclear genes". Molecular Biology and Evolution. 21 (9): 1643–1660. doi:10.1093/molbev/msh160. PMID 15155797.
  26. ^ Woese CR (June 2002). "On the evolution of cells". Proceedings of the National Academy of Sciences of the United States of America. 99 (13): 8742–8747. Bibcode:2002PNAS...99.8742W. doi:10.1073/pnas.132266999. PMC 124369. PMID 12077305.
  27. ^ Koch AL, Silver S (2005). The first cell. Advances in Microbial Physiology. Vol. 50. pp. 227–59. doi:10.1016/S0065-2911(05)50006-7. ISBN 9780120277506. PMID 16221582.
  28. ^ Woese CR (June 2002). "On the evolution of cells". Proceedings of the National Academy of Sciences of the United States of America. 99 (13): 8742–8747. Bibcode:2002PNAS...99.8742W. doi:10.1073/pnas.132266999. PMC 124369. PMID 12077305.

This article incorporates material from the Citizendium article "Evolution of cells", which is licensed under the Creative Commons Attribution-ShareAlike 3.0 Unported License but not under the GFDL.

Further reading

  • Lerat E, Daubin V, Ochman H, Moran NA (May 2005). "Evolutionary origins of genomic repertoires in bacteria". PLOS Biology. 3 (5): e130. doi:10.1371/journal.pbio.0030130. PMC 1073693. PMID 15799709.  
  • Steenkamp ET, Wright J, Baldauf SL (January 2006). "The protistan origins of animals and fungi". Molecular Biology and Evolution. 23 (1): 93–106. doi:10.1093/molbev/msj011. PMID 16151185.
  • Forterre P (March 2006). "Three RNA cells for ribosomal lineages and three DNA viruses to replicate their genomes: a hypothesis for the origin of cellular domain". Proceedings of the National Academy of Sciences of the United States of America. 103 (10): 3669–3674. Bibcode:2006PNAS..103.3669F. doi:10.1073/pnas.0510333103. PMC 1450140. PMID 16505372.

External links

  • Life on Earth
  • The universal nature of biochemistry
  • Endosymbiosis and The Origin of Eukaryotes 22 June 2017 at the Wayback Machine

August 23, 2023
evolution, cells, also, abiogenesis, protocell, cytogenesis, redirects, here, confused, with, citogenesis, refers, evolutionary, origin, subsequent, evolutionary, development, cells, cells, first, emerged, least, billion, years, approximately, million, years, . See also Abiogenesis and Protocell Cytogenesis redirects here Not to be confused with Citogenesis Evolution of cells refers to the evolutionary origin and subsequent evolutionary development of cells Cells first emerged at least 3 8 billion years ago 1 2 3 approximately 750 million years after Earth was formed 4 Contents 1 The first cells 2 Community metabolism 3 Genetic code and the RNA world 4 Sexual reproduction 5 Horizontal gene transfer 6 Canonical patterns 7 Using genomics to infer early lines of evolution 8 Quotes 9 References 10 Further reading 11 External linksThe first cells EditMain articles Abiogenesis and Earliest known life forms The initial development of the cell marked the passage from prebiotic chemistry to partitioned units resembling modern cells The final transition to living entities that fulfill all the definitions of modern cells depended on the ability to evolve effectively by natural selection This transition has been called the Darwinian transition If life is viewed from the point of view of replicator molecules cells satisfy two fundamental conditions protection from the outside environment and confinement of biochemical activity The former condition is needed to keep complex molecules stable in a varying and sometimes aggressive environment the latter is fundamental for the evolution of biocomplexity If freely floating molecules that code for enzymes are not enclosed in cells the enzymes will automatically benefit neighboring replicator molecules as well Thus the consequences of diffusion in non partitioned lifeforms would result in parasitism by default Therefore the selection pressure on replicator molecules will be lower as the lucky molecule that produces the better enzyme does not fully leverage its advantage over its close neighbors In contrast if the molecule is enclosed in a cell membrane the enzymes coded will be available only to itself That molecule will uniquely benefit from the enzymes it codes for increasing individuality and thus accelerating natural selection Partitioning may have begun from cell like spheroids formed by proteinoids which are observed by heating amino acids with phosphoric acid as a catalyst They bear much of the basic features provided by cell membranes Proteinoid based protocells enclosing RNA molecules could have been the first cellular life forms on Earth 5 Another possibility is that the shores of the ancient coastal waters may have been a suitable environment for the initial development of cells Waves breaking on the shore create a delicate foam composed of bubbles Shallow coastal waters also tend to be warmer further concentrating the molecules through evaporation While bubbles made mostly of water tend to burst quickly oily bubbles are much more stable The phospholipid the primary material of cell membranes is an example of a common oily compound prevalent in the prebiotic seas 6 Both of these options require the presence of massive amounts of chemicals and organic material in order to form cells A large gathering of organic molecules most likely came from what scientists now call the prebiotic soup The prebiotic soup refers to the collection of every organic compound that appeared on Earth after it was formed This soup would have most likely contained the compounds necessary to form early cells 7 Phospholipids are composed of a hydrophilic head on one end and a hydrophobic tail on the other They can come together to form a bilayer membrane A lipid monolayer bubble can only contain oil and is not conducive to harboring water soluble organic molecules On the other hand a lipid bilayer bubble can contain water and was a likely precursor to the modern cell membrane citation needed If a protein was introduced that increased the integrity of its parent bubble then that bubble had an advantage citation needed Primitive reproduction may have occurred when the bubbles burst releasing the results of the experiment into the surrounding medium Once enough of the right compounds were released into the medium the development of the first prokaryotes eukaryotes and multi cellular organisms could be achieved 8 citation needed However the first cell membrane could not have been composed of phospholipids due its low permeability as ions would not able to pass through the membrane Rather it is suggested they were composed of fatty acids as they can freely exchange ions allowing geochemically sustained proton gradients at alkaline hydrothermal vents that might lead to prebiotic chemical reactions via CO2 fixation 9 Community metabolism EditThe common ancestor of the now existing cellular lineages eukaryotes bacteria and archaea may have been a community of organisms that readily exchanged components and genes It would have contained Autotrophs that produced organic compounds from CO2 either photosynthetically or by inorganic chemical reactions Heterotrophs that obtained organics from leakage of other organisms Saprotrophs that absorbed nutrients from decaying organisms Phagotrophs that were sufficiently complex to envelop and digest particulate nutrients including other organisms The eukaryotic cell seems to have evolved from a symbiotic community of prokaryotic cells DNA bearing organelles like mitochondria and chloroplasts are remnants of ancient symbiotic oxygen breathing bacteria and cyanobacteria respectively where at least part of the rest of the cell may have been derived from an ancestral archaean prokaryote cell The archean prokaryote cell concept is often termed as the endosymbiotic theory There is still debate about whether organelles like the hydrogenosome predated the origin of mitochondria or vice versa see the hydrogen hypothesis for the origin of eukaryotic cells How the current lineages of microbes evolved from this postulated community is currently unsolved but subject to intense research by biologists stimulated by the great flow of new discoveries in genome science 10 Genetic code and the RNA world EditModern evidence suggests that early cellular evolution occurred in a biological realm radically distinct from modern biology It is thought that in this ancient realm the current genetic role of DNA was largely filled by RNA and catalysis was also largely mediated by RNA that is by ribozyme counterparts of enzymes This concept is known as the RNA world hypothesis According to this hypothesis the ancient RNA world transitioned into the modern cellular world via the evolution of protein synthesis followed by replacement of many cellular ribozyme catalysts by protein based enzymes Proteins are much more flexible in catalysis than RNA due to the existence of diverse amino acid side chains with distinct chemical characteristics The RNA record in existing cells appears to preserve some molecular fossils from this RNA world These RNA fossils include the ribosome itself in which RNA catalyzes peptide bond formation the modern ribozyme catalyst RNase P and RNAs 11 12 13 14 The nearly universal genetic code preserves some evidence for the RNA world For instance recent studies of transfer RNAs the enzymes that charge them with amino acids the first step in protein synthesis and the way these components recognize and exploit the genetic code have been used to suggest that the universal genetic code emerged before the evolution of the modern amino acid activation method for protein synthesis 11 12 15 16 17 The first RNA polymers probably emerged prior to 4 17 Gya if life originated at freshwater environments similar to Darwin s warm little pond 18 Sexual reproduction EditThe evolution of sexual reproduction may be a primordial and fundamental characteristic of eukaryotes including single cell eukaryotes Based on a phylogenetic analysis Dacks and Roger 19 proposed that facultative sex was present in the common ancestor of all eukaryotes Hofstatter and Lehr 20 reviewed evidence supporting the hypothesis that all eukaryotes can be regarded as sexual unless proven otherwise Sexual reproduction may have arisen in early protocells with RNA genomes RNA world 21 Initially each protocell would likely have contained one RNA genome rather than multiple since this maximizes the growth rate However the occurrence of damages to the RNA which block RNA replication or interfere with ribozyme function would make it advantageous to fuse periodically with another protocell to restore reproductive ability This early simple form of genetic recovery is similar to that occurring in extant segmented single stranded RNA viruses see influenza A virus As duplex DNA became the predominant form of the genetic material the mechanism of genetic recovery evolved into the more complex process of meiotic recombination found today in most species It thus appears likely that sexual reproduction arose early in the evolution of cells and has had a continuous evolutionary history Horizontal gene transfer EditHorizontal gene transfer HGT is the movement of genetic information between different organisms of the same species mainly being bacteria This is not the movement of genetic information between a parent and their offspring but by other factors In contrast to how animals reproduce and evolve from sexual reproduction bacteria evolve by sharing DNA with other bacteria or their environment There are three common mechanisms of transferring genetic material by HGT Transformation The bacteria assimilates DNA from the environment into their own Conjugation Bacteria directly transfer genes from one cell to another Transduction Bacteriophages virus move genes from one bacterial cell to anotherOnce one of these mechanisms has occurred the bacteria will continue to multiply and grow resistance and evolve by natural selection HGT is the main cause of the assimilation of certain genetic material and the passing down of antibiotic resistance genes ARGs Canonical patterns EditAlthough the evolutionary origins of the major lineages of modern cells are disputed the primary distinctions between the three major lineages of cellular life called domains are firmly established In each of these three domains DNA replication transcription and translation all display distinctive features There are three versions of ribosomal RNAs and generally three versions of each ribosomal protein one for each domain of life These three versions of the protein synthesis apparatus are called the canonical patterns and the existence of these canonical patterns provides the basis for a definition of the three domains Bacteria Archaea and Eukarya or Eukaryota of currently existing cells 22 Using genomics to infer early lines of evolution EditInstead of relying a single gene such as the small subunit ribosomal RNA SSU rRNA gene to reconstruct early evolution or a few genes scientific effort has shifted to analyzing complete genome sequences 23 Evolutionary trees based only on SSU rRNA alone do not capture the events of early eukaryote evolution accurately and the progenitors of the first nucleated cells are still uncertain For instance analysis of the complete genome of the eukaryote yeast shows that many of its genes are more closely related to bacterial genes than they are to archaea and it is now clear that archaea were not the simple progenitors of the eukaryotes in contradiction to earlier findings based on SSU rRNA and limited samples of other genes 24 One hypothesis is that the first nucleated cell arose from two distinctly different ancient prokaryotic non nucleated species that had formed a symbiotic relationship with one another to carry out different aspects of metabolism One partner of this symbiosis is proposed to be a bacterial cell and the other an archaeal cell It is postulated that this symbiotic partnership progressed via the cellular fusion of the partners to generate a chimeric or hybrid cell with a membrane bound internal structure that was the forerunner of the nucleus The next stage in this scheme was transfer of both partner genomes into the nucleus and their fusion with one another Several variations of this hypothesis for the origin of nucleated cells have been suggested 25 Other biologists dispute this conception 10 and emphasize the community metabolism theme the idea that early living communities would comprise many different entities to extant cells and would have shared their genetic material more extensively than current microbes 26 Quotes Edit The First Cell arose in the previously prebiotic world with the coming together of several entities that gave a single vesicle the unique chance to carry out three essential and quite different life processes These were a to copy informational macromolecules b to carry out specific catalytic functions and c to couple energy from the environment into usable chemical forms These would foster subsequent cellular evolution and metabolism Each of these three essential processes probably originated and was lost many times prior to The First Cell but only when these three occurred together was life jump started and Darwinian evolution of organisms began Koch and Silver 2005 27 The evolution of modern cells is arguably the most challenging and important problem the field of Biology has ever faced In Darwin s day the problem could hardly be imagined For much of the 20th century it was intractable In any case the problem lay buried in the catch all rubric origin of life where because it is a biological not a bio chemical problem it was effectively ignored Scientific interest in cellular evolution started to pick up once the universal phylogenetic tree the framework within which the problem had to be addressed was determined But it was not until microbial genomics arrived on the scene that biologists could actually do much about the problem of cellular evolution Carl Woese 2002 28 References Edit Schopf JW Kudryavtsev AB Czaja AD and Tripathi AB 2007 Evidence of Archean life Stromatolites and microfossils Precambrian Research 158 141 155 Schopf JW 2006 Fossil evidence of Archaean life Philos Trans R Soc Lond B Biol Sci 29 361 1470 869 85 Raven PH Johnson GB 2002 Biology McGraw Hill Education p 68 ISBN 978 0 07 112261 0 Retrieved 7 July 2013 Cooper GM 2000 The Origin and Evolution of Cells The Cell A Molecular Approach 2nd ed Fox SW Dose K 1972 Molecular evolution and the origin of life San Francisco W H Freeman ISBN 978 0 7167 0163 7 OCLC 759538 Big Picture Big Picture Retrieved 1 October 2019 The Prebiotic Soup earthguide ucsd edu Retrieved 1 October 2019 This theory is expanded upon in The Cell Evolution of the First Organism by Joseph Panno Nunes Palmeira Raquel Colnaghi Marco Harrison Stuart A Pomiankowski Andrew Lane Nick 9 November 2022 The limits of metabolic heredity in protocells Proceedings of the Royal Society B Biological Sciences 289 1986 doi 10 1098 rspb 2022 1469 ISSN 0962 8452 PMC 9653231 PMID 36350219 a b Kurland CG Collins LJ Penny D May 2006 Genomics and the irreducible nature of eukaryote cells Science 312 5776 1011 1014 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12805538 S2CID 42394233 Henz SR Huson DH Auch AF Nieselt Struwe K Schuster SC May 2005 Whole genome prokaryotic phylogeny Bioinformatics 21 10 2329 2335 doi 10 1093 bioinformatics bth324 PMID 15166018 Esser C Ahmadinejad N Wiegand C Rotte C Sebastiani F Gelius Dietrich G et al September 2004 A genome phylogeny for mitochondria among alpha proteobacteria and a predominantly eubacterial ancestry of yeast nuclear genes Molecular Biology and Evolution 21 9 1643 1660 doi 10 1093 molbev msh160 PMID 15155797 Esser C Ahmadinejad N Wiegand C Rotte C Sebastiani F Gelius Dietrich G et al September 2004 A genome phylogeny for mitochondria among alpha proteobacteria and a predominantly eubacterial ancestry of yeast nuclear genes Molecular Biology and Evolution 21 9 1643 1660 doi 10 1093 molbev msh160 PMID 15155797 Woese CR June 2002 On the evolution of cells Proceedings of the National Academy of Sciences of the United States of America 99 13 8742 8747 Bibcode 2002PNAS 99 8742W doi 10 1073 pnas 132266999 PMC 124369 PMID 12077305 Koch AL Silver S 2005 The first cell Advances in Microbial Physiology Vol 50 pp 227 59 doi 10 1016 S0065 2911 05 50006 7 ISBN 9780120277506 PMID 16221582 Woese CR June 2002 On the evolution of cells Proceedings of the National Academy of Sciences of the United States of America 99 13 8742 8747 Bibcode 2002PNAS 99 8742W doi 10 1073 pnas 132266999 PMC 124369 PMID 12077305 This article incorporates material from the Citizendium article Evolution of cells which is licensed under the Creative Commons Attribution ShareAlike 3 0 Unported License but not under the GFDL Further reading EditLerat E Daubin V Ochman H Moran NA May 2005 Evolutionary origins of genomic repertoires in bacteria PLOS Biology 3 5 e130 doi 10 1371 journal pbio 0030130 PMC 1073693 PMID 15799709 Steenkamp ET Wright J Baldauf SL January 2006 The protistan origins of animals and fungi Molecular Biology and Evolution 23 1 93 106 doi 10 1093 molbev msj011 PMID 16151185 Forterre P March 2006 Three RNA cells for ribosomal lineages and three DNA viruses to replicate their genomes a hypothesis for the origin of cellular domain Proceedings of the National Academy of Sciences of the United States of America 103 10 3669 3674 Bibcode 2006PNAS 103 3669F doi 10 1073 pnas 0510333103 PMC 1450140 PMID 16505372 External links EditLife on Earth The universal nature of biochemistry Endosymbiosis and The Origin of Eukaryotes Archived 22 June 2017 at the Wayback Machine Origins of the Eukarya Retrieved from https en wikipedia org w index php title Evolution of cells amp oldid 1171514164, wikipedia, wiki, book, books, library,

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