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Crown Eukaryotes
Taking into account the definition of a crown group, crown eukaryotes could be seen as the aggrupation of all lineages descending from LECA (Last Eukarytotic Common Ancestor). This comprises a huge ensemble of taxa that seemingly diverged simultaneously and that conform the vast majority of the eukaryotic life, plants, fungi, animals and the variety of protist lineages. According to ribosomal RNA data, the radiation of eukaryotes from LECA would have originated from a series of basal lineages that branched off successively at this early stage. The hallmark of these organisms pertaining to crown eukaryotes is a higher complexity of their genetic and cellular machinery as compared with prokaryotes, enabled by their cellular compartmentalization. This complexity is accompanied by others extra cell-morphological features: endo/exocytosis, sexual reproduction, multicellularity, and vertical inheritance (as opposed to the horizontal gene transfer common among prokaryotes), that have l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aigarchaeota
The "Aigarchaeota" are a proposed archaeal phylum of which the main representative is '' Caldiarchaeum subterraneum''.. It is not yet clear if this represents a new phylum or a and order of the Nitrososphaerota, since the genome of ''Caldiarchaeum subterraneum'' encodes several Nitrososphaerota-like features. The name "''Aigarchaeota''" comes from the Greek , ''avgí'', meaning "dawn" or "aurora", for the intermediate features of hyperthermophilic and mesophilic life during the evolution of its lineage. Taxonomy * Genus "''Candidatus'' Caldarchaeum" corrig. Nunoura et al. 2011 ** "''Ca.'' C. subterraneum" corrig. Nunoura et al. 2011 * Genus "''Candidatus'' Calditenuis" Beam et al. 2016 ** "''Ca.'' C. aerorheumensis" Beam et al. 2016 See also * List of Archaea genera This article lists the genera of the Archaea. The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI). ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tappania
''Tappania'' is an acanthomorph acritarch found in late Paleoproterozoic, Mesoproterozoic and Neoproterozoic rocks. The oldest examples are around 1630 million years old, making them the oldest known evidence of Eukaryotes in the fossil record. * ''Tappania plana'' appears in Paleoproterozoic formations of India (Deonar Deonar is a suburb of Mumbai. It has gained prominence for being the location of the largest dumping ground in Asia and also the location of city's largest abattoir, Deonar Municipal Abattoir. Important Landmarks India's largest abattoir is ...) and northern China ( Baicaoping and Beidajian), both with an age of 1,630 mya. It is a roughly spherical acritarch, 30-60 μm in diameter, with one or two small necks. Small branched and / or partitioned tubes emerge from the central body. * ''Tappania'' sp. It appears in deposits of the Neoproterozoic in northern Australia, northwestern US and central Siberia, with an age of up to 850 mya and 200-300 mya strat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paleoproterozoic
The Paleoproterozoic Era (;, also spelled Palaeoproterozoic), spanning the time period from (2.5–1.6 Ga), is the first of the three sub-divisions (eras) of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's geological history. It was during this era that the continents first stabilized. Paleontological evidence suggests that the Earth's rotational rate ~1.8 billion years ago equated to 20-hour days, implying a total of ~450 days per year. Atmosphere Before the enormous increase in atmospheric oxygen, almost all existing lifeforms were anaerobic organisms whose metabolism was based on a form of cellular respiration that did not require oxygen. Free oxygen in large amounts is toxic to most anaerobic organisms. Consequently, most died when the atmospheric free oxygen levels soared in an extinction event called the Great Oxidation Event, which brought atmospheric oxygen levels to up to 10% of their current level. The only creatures that survi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acritarch
Acritarchs are organic microfossils, known from approximately 1800 million years ago to the present. The classification is a catch all term used to refer to any organic microfossils that cannot be assigned to other groups. Their diversity reflects major ecological events such as the appearance of predation and the Cambrian explosion. Definition Acritarchs were originally defined as non-acid soluble (i.e. non-carbonate, non-siliceous) organic-walled microfossils consisting of a central cavity, and whose biological affinities cannot be determined with certainty. Most commonly they are composed of thermally altered acid insoluble carbon compounds (kerogen). Acritarchs may include the remains of a wide range of quite different kinds of organisms—ranging from the egg cases of small metazoans to resting cysts of many kinds of chlorophyta (green algae). It is likely that most acritarch species from the Paleozoic represent various stages of the life cycle of algae that were ancestral ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Endosymbiont Hypothesis
Symbiogenesis (endosymbiotic theory, or serial endosymbiotic theory,) is the leading evolutionary theory of the origin of eukaryotic cells from prokaryotic organisms. The theory holds that mitochondria, plastids such as chloroplasts, and possibly other organelles of eukaryotic cells are descended from formerly free-living prokaryotes (more closely related to the Bacteria than to the Archaea) taken one inside the other in endosymbiosis. Mitochondria appear to be phylogenetically related to Rickettsiales bacteria, while chloroplasts are thought to be related to cyanobacteria. The idea that chloroplasts were originally independent organisms that merged into a symbiotic relationship with other one-celled organisms dates back to the 19th century, when it was espoused by researchers such as Andreas Schimper. The endosymbiotic theory was articulated in 1905 and 1910 by the Russian botanist Konstantin Mereschkowski, and advanced and substantiated with microbiological evidence by Lynn Mar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cytokine
Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in autocrine, paracrine and endocrine signaling as immunomodulating agents. Cytokines include chemokines, interferons, interleukins, lymphokines, and tumour necrosis factors, but generally not hormones or growth factors (despite some overlap in the terminology). Cytokines are produced by a broad range of cells, including immune cells like macrophages, B lymphocytes, T lymphocytes and mast cells, as well as endothelial cells, fibroblasts, and various stromal cells; a given cytokine may be produced by more than one type of cell. They act through cell surface receptors and are especially important in the immune system; cytokines modulate the balance between humoral and cell-based immune responses, and they regulate the maturation, growth, and res ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cytoskeleton
The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is composed of similar proteins in the various organisms. 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. A multitude of functions can be performed by the cytoskeleton. Its primary function is to give the cell its shape and mechanical resistance to deformation, and through association with extracellular connective tissue and other cells it stabilizes entire tissues. The cytoskeleton can also contract, thereby deforming the cell and the cell's environment and allowing cells to migrate. Moreover, it is involved in many cell signaling pathways and in the uptake of extracellular material ( endocytosis), the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alphaproteobacteria
Alphaproteobacteria is a class of bacteria in the phylum Pseudomonadota (formerly Proteobacteria). The Magnetococcales and Mariprofundales are considered basal or sister to the Alphaproteobacteria. The Alphaproteobacteria are highly diverse and possess few commonalities, but nevertheless share a common ancestor. Like all ''Proteobacteria'', its members are gram-negative and some of its intracellular parasitic members lack peptidoglycan and are consequently gram variable. Characteristics The Alphaproteobacteria are a diverse taxon and comprises several phototrophic genera, several genera metabolising C1-compounds (''e.g.'', ''Methylobacterium'' spp.), symbionts of plants (''e.g.'', ''Rhizobium'' spp.), endosymbionts of arthropods (''Wolbachia'') and intracellular pathogens (''e.g. Rickettsia''). Moreover, the class is sister to the protomitochondrion, the bacterium that was engulfed by the eukaryotic ancestor and gave rise to the mitochondria, which are organelles in eukaryotic ce ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Molecular Clock
The molecular clock is a figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged. The biomolecular data used for such calculations are usually nucleotide sequences for DNA, RNA, or amino acid sequences for proteins. The benchmarks for determining the mutation rate are often fossil or archaeological dates. The molecular clock was first tested in 1962 on the hemoglobin protein variants of various animals, and is commonly used in molecular evolution to estimate times of speciation or radiation. It is sometimes called a gene clock or an evolutionary clock. Early discovery and genetic equidistance The notion of the existence of a so-called "molecular clock" was first attributed to Émile Zuckerkandl and Linus Pauling who, in 1962, noticed that the number of amino acid differences in hemoglobin between different lineages changes roughly linearly with time, as estimated from fossil evidence. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Taphonomic Loss
Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efremov to describe the study of the transition of remains, parts, or products of organisms from the biosphere to the lithosphere. The term taphomorph is used to describe fossil structures that represent poorly-preserved, deteriorated remains of a mixture of taxonomic groups, rather than of a single one. Description Taphonomic phenomena are grouped into two phases: biostratinomy, events that occur between death of the organism and the burial; and diagenesis, events that occur after the burial. Since Efremov's definition, taphonomy has expanded to include the fossilization of organic and inorganic materials through both cultural and environmental influences. This is a multidisciplinary concept and is used in slightly different contexts through ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eukaryogenesis
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacteria and Archaea (both prokaryotes) make up the other two domains. The eukaryotes are usually now regarded as having emerged in the Archaea or as a sister of the Asgard archaea. This implies that there are only two domains of life, Bacteria and Archaea, with eukaryotes incorporated among archaea. Eukaryotes represent a small minority of the number of organisms, but, due to their generally much larger size, their collective global biomass is estimated to be about equal to that of prokaryotes. Eukaryotes emerged approximately 2.3–1.8 billion years ago, during the Proterozoic eon, likely as flagellated phagotrophs. Their name comes from the Greek εὖ (''eu'', "well" or "good") and κάρυον (''karyon'', "nut" or "kernel"). ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
