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Non-cellular Life
Non-cellular life, also known as acellular life, is life that exists without a cellular structure for at least part of its life cycle. Historically, most definitions of life postulated that an organism must be composed of one or more cells, but, for some, this is no longer considered necessary, and modern criteria allow for forms of life based on other structural arrangements. Nucleic acid-containing infectious agents Viruses Researchers initially described viruses as "poisons" or "toxins", then as "infectious proteins"; but they possess genetic material, a defined structure, and the ability to spontaneously assemble from their constituent parts. This has spurred extensive debate as to whether they should be regarded as fundamentally biotic or abiotic—as very small biological organisms or as very large biochemical molecules. Without their hosts, they are not able to perform any of the functions of life—such as metabolism, growth, or reproduction. Since the 195 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Syncytial
A syncytium (; : syncytia; from Greek: σύν ''syn'' "together" and κύτος ''kytos'' "box, i.e. cell") or symplasm is a multinucleate cell that can result from multiple cell fusions of uninuclear cells (i.e., cells with a single nucleus), in contrast to a coenocyte, which can result from multiple nuclear divisions without accompanying cytokinesis. The muscle cell that makes up animal skeletal muscle is a classic example of a syncytium cell. The term may also refer to cells interconnected by specialized membranes with gap junctions, as seen in the heart muscle cells and certain smooth muscle cells, which are synchronized electrically in an action potential. The field of embryogenesis uses the word ''syncytium'' to refer to the coenocytic blastoderm embryos of invertebrates, such as ''Drosophila melanogaster''. Physiological examples Protists In protists, syncytia can be found in some rhizarians (e.g., chlorarachniophytes, plasmodiophorids, haplosporidians) and acellula ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RNA Polymerase II
RNA polymerase II (RNAP II and Pol II) is a Protein complex, multiprotein complex that Transcription (biology), transcribes DNA into precursors of messenger RNA (mRNA) and most small nuclear RNA (snRNA) and microRNA. It is one of the three RNA polymerase, RNAP enzymes found in the nucleus of eukaryote, eukaryotic cells. A 550 kDa complex of 12 subunits, RNAP II is the most studied type of RNA polymerase. A wide range of transcription factors are required for it to bind to upstream gene promoter (biology), promoters and begin transcription. Discovery Early studies suggested a minimum of two RNAPs: one which synthesized rRNA in the nucleolus, and one which synthesized other RNA in the nucleoplasm, part of the nucleus but outside the nucleolus. In 1969, biochemists Robert G. Roeder and William J. Rutter, William Rutter discovered there are total three distinct nuclear RNA polymerases, an additional RNAP that was responsible for transcription of some kind of RNA in the nucleoplasm. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plasmid
A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria and archaea; however plasmids are sometimes present in and eukaryotic organisms as well. Plasmids often carry useful genes, such as those involved in antibiotic resistance, virulence, secondary metabolism and bioremediation. While chromosomes are large and contain all the essential genetic information for living under normal conditions, plasmids are usually very small and contain additional genes for special circumstances. Artificial plasmids are widely used as vectors in molecular cloning, serving to drive the replication of recombinant DNA sequences within host organisms. In the laboratory, plasmids may be introduced into a cell via transformation. Synthetic plasmids are available for procurement over the internet by various vendors ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nanobe
A nanobe () is a tiny filamental structure first found in some rocks and sediments. Some scientists hypothesize that nanobes are the smallest form of life, the size of the smallest known bacteria. No conclusive evidence exists that these structures are, or are not, living organisms, so their classification is controversial. The 1996 discovery of nanobes was published in 1998 by Uwins ''et al.'', from the University of Queensland, Australia. They were found growing from rock samples (both full-diameter and sidewall cores) of Jurassic and Triassic sandstones, originally retrieved from an unspecified number of oil exploration wells off Australia's west coast. Depths of retrieval were between and below the sea bed. While Uwins ''et al.'' present assertions against it, they do not exclude the possibility that the nanobes are from a surface contaminant, not from the rock units cited. The smallest are just 20 nanometers in diameter. Some researchers believe that these structu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hypothetical Types Of Biochemistry
Several forms of biochemistry are agreed to be scientifically viable but are not proven to exist at this time. The kinds of life, living organisms currently known on Earth all use carbon compounds for basic structural and metabolism, metabolic functions, water as a solvent, and DNA or RNA to define and control their form. If life exists on other planets or natural satellite, moons it may be chemically similar, though it is also possible that there are organisms with quite different chemistries for instance, involving other classes of carbon compounds, compounds of another element, or another solvent in place of water. The possibility of life-forms being based on "alternative" biochemistries is the topic of an ongoing scientific discussion, informed by what is known about extraterrestrial environments and about the chemical behaviour of various elements and compounds. It is of interest in synthetic biology and is also a science fiction theme, common subject in science fiction. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbon Chauvinism
Carbon chauvinism is a neologism meant to disparage the assumption that the chemical processes of hypothetical extraterrestrial life must be constructed primarily from carbon (organic compounds) because as far as is known, carbon's chemical and thermodynamic properties render it far superior to all other elements at forming molecules used in living organisms. The expression "carbon chauvinism" is also used to criticize the idea that artificial intelligence cannot in theory be sentient or truly intelligent because the underlying matter is not biological. Furthermore, the term is used by transhumanists to object to the commonly held view that life has an inherently higher moral value than hypothetical artificial consciousness. Concept The term was used as early as 1973, when scientist Carl Sagan described it and other human chauvinisms that limit imagination of possible extraterrestrial life. It suggests that human beings, as carbon-based life forms who have never encountered ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Last Universal Common Ancestor
The last universal common ancestor (LUCA) is the hypothesized common ancestral cell from which the three domains of life, the Bacteria, the Archaea, and the Eukarya originated. The cell had a lipid bilayer; it possessed the genetic code and ribosomes which translated from DNA or RNA to proteins. Although the timing of the LUCA is not able to be definitively constrained, most studies suggest that the LUCA existed by or prior to 3.5 billion years ago, and possibly as early as 4.3 billion years ago or earlier. The nature of this point or stage of divergence remains a topic of research. All earlier forms of life preceding this divergence and all extant organisms are generally thought to share common ancestry. On the basis of a formal statistical test, this theory of a universal common ancestry (UCA) is supported versus competing multiple-ancestry hypotheses. The first universal common ancestor (FUCA) is a hypothetical non-cellular ancestor to LUCA and other now-extinct s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
First Universal Common Ancestor
The first universal common ancestor (FUCA) is thought to be a non-cellular entity that was the earliest organism with a genetic code capable of biological translation of RNA molecules into peptides to produce proteins. Its descendants would include the last universal common ancestor (LUCA) and every modern cell. FUCA would also be the ancestor of ancient sister lineages of LUCA, none of which have modern descendants, but which are thought to have horizontally transferred some of their genes into the genome of early descendants of LUCA. FUCA is thought to have been composed of progenotes, proposed ancient biological systems that would have used RNA for their genome and self-replication. By comparison, LUCA would have had a complex metabolism and a DNA genome with hundreds of genes and gene families. Origins Long before the appearance of compartmentalized biological entities like FUCA, life had already begun to organize itself and emerge in a hypothesized pre-cellular era ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gut Bacteria
Gut microbiota, gut microbiome, or gut flora are the microorganisms, including bacteria, archaea, fungi, and viruses, that live in the digestive tracts of animals. The gastrointestinal metagenome is the aggregate of all the genomes of the gut microbiota. The gut is the main location of the human microbiome. The gut microbiota has broad impacts, including effects on colonization, resistance to pathogens, maintaining the intestinal epithelium, metabolizing dietary and pharmaceutical compounds, controlling immune function, and even behavior through the gut–brain axis. The microbial composition of the gut microbiota varies across regions of the digestive tract. The colon contains the highest microbial density of any human-associated microbial community studied so far, representing between 300 and 1000 different species. Bacteria are the largest and to date, best studied component and 99% of gut bacteria come from about 30 or 40 species. About 55% of the dry mass of feces is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microbiome
A microbiome () is the community of microorganisms that can usually be found living together in any given habitat. It was defined more precisely in 1988 by Whipps ''et al.'' as "a characteristic microbial community occupying a reasonably well-defined habitat which has distinct physio-chemical properties. The term thus not only refers to the microorganisms involved but also encompasses their theatre of activity". In 2020, an international panel of experts published the outcome of their discussions on the definition of the microbiome. They proposed a definition of the microbiome based on a revival of the "compact, clear, and comprehensive description of the term" as originally provided by Whipps ''et al.'', but supplemented with two explanatory paragraphs, the #First explanatory paragraph, first pronouncing the dynamic character of the microbiome, and the #Second explanatory paragraph, second clearly separating the term ''microbiota'' from the term ''microbiome''. Modified text ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Obelisk (life Form)
An obelisk is a microscopic genetic element that consists of a type of infectious agent composed of RNA. Described as a "viroid-like element", they consist of RNA in a circular rod shape without any protein shell coating. Obelisks were identified in 2024 through computational analysis of vast genetic datasets. Their RNA sequences are entirely novel, and their placement within the tree of life remains uncertain as they do not appear to have a shared ancestry with any other life form, virus, or viroid. Obelisks are currently classified as an enigmatic taxon, forming a distinct phylogenetic group. Discovery Obelisks were first described in a January 2024 preprint, by Stanford University (USA), Valencia University (Spain) and University of Toronto (Canada) scientists which sifted through genetic data. Currently, only a few methods are available for the identification of these elements from NGS data. The authors of the paper say that "Obelisks form their own distinct phyl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
The New York Times
''The New York Times'' (''NYT'') is an American daily newspaper based in New York City. ''The New York Times'' covers domestic, national, and international news, and publishes opinion pieces, investigative reports, and reviews. As one of the longest-running newspapers in the United States, the ''Times'' serves as one of the country's Newspaper of record, newspapers of record. , ''The New York Times'' had 9.13 million total and 8.83 million online subscribers, both by significant margins the List of newspapers in the United States, highest numbers for any newspaper in the United States; the total also included 296,330 print subscribers, making the ''Times'' the second-largest newspaper by print circulation in the United States, following ''The Wall Street Journal'', also based in New York City. ''The New York Times'' is published by the New York Times Company; since 1896, the company has been chaired by the Ochs-Sulzberger family, whose current chairman and the paper's publ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
