Three-domain system

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three-domain system is a biological classification introduced by Carl Woese et al. in 1977 that divided the cellular life form into archaea , bacteria , and eukaryotes domain. In particular, it emphasizes the separation of prokaryotes into two groups, originally called Eubacteria (now Bacteria ) and Archaebacteria (now Archaea >). Woese suggests that, based on the 16S rRNA gene differences, these two groups and eukaryotes appear separately from ancestors with poorly developed genetic machinery, often referred to as progenote. To reflect this primary lineage, he treats each as a domain, divided into several different kingdoms. Woese originally used the term "kingdom" to refer to three main phylogenetic groups, and the nomenclature was widely used until the term "domain" was adopted in 1990.

Portions of the three-domain theory have been challenged by scientists such as Radhey Gupta, who argue that the major divisions in prokaryotes must be among those surrounded by a single membrane, and those with two membranes.

Video Three-domain system

Classification

The three domain system adds the classification level (domain) "above" the existing kingdom within the five or six empire systems previously used. This classification system recognizes the fundamental difference between the two prokaryotic groups, as far as arcaea seems more closely related to eukaryotes than those with other prokaryotic bacteria. The system currently has the following listed empires in three domains:

Archaea Domains - prokaryotes, no nuclear membranes, biochemical markers and different RNAs from bacteria, have a unique ancient evolutionary history that is considered the species of the oldest organism on Earth; traditionally classified as archaebacteria; often characterized by living in extreme environments. Some examples of archaeal organisms are methanogens that produce methane gas, halophiles that live in very salty water, and thermoacidophiles that thrive in acidic high water.

Domain Bacteria - prokaryotic, consisting of prokaryotic cells that have primarily diastyl glycerol lipid diester in their membranes and bacterial rRNA, no nuclear membrane, usually classified as bacteria. Most prokaryotic organisms of pathogens are known to belong to bacteria (see for exceptions), and are currently studied more widely than Archaea. Some examples of bacteria including photosynthesizing bacteria Cyanobacteria associated with chloroplasts eukaryotic plants and algae, Spirochaetes - Gram-negative bacteria are included that cause syphilis and Lyme disease, and bacteria Actinobacteria - Gram-positive including Bifidobacterium animalis is in the human colon.

Eukarya Domains - eukaryotes, organisms containing membrane-bound nuclei. A list of incomplete eukaryotic organisms includes:

• Great Mushrooms or mushrooms
  Example:

• Saccharomycotina - including real yeast
• Basidiomycota - including mushrooms

• Great Plantae or plants
  Example:

• Bryophyta - mosses
• Magnoliophyta - flowering plants

• Animalia Kingdom or animal
  Example:

• Arthropods - including insects, arachnids, and crustaceans
• Chordata - including vertebrates as subphylum

Maps Three-domain system

Niches

Each of the three cell types tends to match a specialization or a recurring role. Bacteria tend to be the most productive reproduction, at least in moderate environments. Arkean tend to adapt quickly to extreme environments, such as high temperature, high acid, high sulfur, etc. This includes adapting to use a variety of food sources. Eukaryotes are the most flexible associated with the formation of cooperative colonies, as in multi-cellular organisms, including humans. In fact, the structure of Eukaryotes probably comes from a combination of different cell types, forming organelles.

Parakaryon myojinensis ( incertae sedis ) is a single-celled organism known as a unique example. "These organisms seem to be different life forms from prokaryotes and eukaryotes", with features both.

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Alternative

Part of the three-domain theory has been challenged by scientists including Ernst Mayr, Thomas Cavalier-Smith, and Radhey S. Gupta. Specifically, Gupta argues that the major divisions in prokaryotes should be among those surrounded by a single membrane (monoderm), including gram-positive bacteria and archaebacteria, and those with inner and outer cell membranes, including gram-negative bacteria. He claims that the sequence of features and phylogeny of some highly sustainable proteins is inconsistent with the theory of three domains, and it must be abandoned despite widespread acceptance.

Recent work has suggested that Eukarya may have actually been branched from the Archea domain. According to Spang et al. Lokiarchaeota form monophyletic groups with eukaryotes in phylogenic analysis. The related genome also encodes an expanded repertoire of eukaryotic signature proteins that demonstrate advanced membrane remodeling capabilities. This data suggests a two-domain system that conflicts with the classic three-domain system.

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See also

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References

Source of the article : Wikipedia