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RNA-based Evolution
RNA-based evolution is a theory that posits that RNA is not merely an intermediate between Watson and Crick model of the DNA molecule and proteins, but rather a far more dynamic and independent role-player in determining phenotype. By regulating the Transcription (genetics), transcription in DNA sequences, the stability of RNA, and the capability of messenger RNA to be Translation (biology), translated, RNA processing events allow for a diverse array of proteins to be synthesized from a single gene. Since RNA processing is heritable, it is subject to natural selection suggested by Darwin and contributes to the evolution and diversity of most eukaryotic organisms. Role of RNA in conventional evolution In accordance with the central dogma of molecular biology, RNA passes information between the DNA of a genome and the proteins expressed within an organism. Therefore, from an evolutionary standpoint, a mutation within the DNA bases results in an alteration of the RNA transcripts, wh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Theory
A theory is a rational type of abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinking is often associated with such processes as observational study or research. Theories may be scientific, belong to a non-scientific discipline, or no discipline at all. Depending on the context, a theory's assertions might, for example, include generalized explanations of how nature works. The word has its roots in ancient Greek, but in modern use it has taken on several related meanings. In modern science, the term "theory" refers to scientific theories, a well-confirmed type of explanation of nature, made in a way consistent with the scientific method, and fulfilling the criteria required by modern science. Such theories are described in such a way that scientific tests should be able to provide empirical support for it, or empirical contradiction ("falsify") of it. Scientific theories are the most reliable, rigorous, and compr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Catalyze
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quickly, very small amounts of catalyst often suffice; mixing, surface area, and temperature are important factors in reaction rate. Catalysts generally react with one or more reactants to form intermediates that subsequently give the final reaction product, in the process of regenerating the catalyst. Catalysis may be classified as either homogeneous, whose components are dispersed in the same phase (usually gaseous or liquid) as the reactant, or heterogeneous, whose components are not in the same phase. Enzymes and other biocatalysts are often considered as a third category. Catalysis is ubiquitous in chemical industry of all kinds. Estimates are that 90% of all commercially produced chemical products involve catalysts at some stag ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RNA World
The RNA world is a hypothetical stage in the evolutionary history of life on Earth, in which self-replicating RNA molecules proliferated before the evolution of DNA and proteins. The term also refers to the hypothesis that posits the existence of this stage. Alexander Rich first proposed the concept of the RNA world in 1962, and Walter Gilbert coined the term in 1986. Alternative chemical paths to life have been proposed, and RNA-based life may not have been the first life to exist. Even so, the evidence for an RNA world is strong enough that the hypothesis has gained wide acceptance. The concurrent formation of all four RNA building blocks further strengthened the hypothesis. Regardless of its plausibility in a prebiotic scenario, the RNA world can serve as a model system for studying the origin of life. Like DNA, RNA can store and replicate genetic information; like protein enzymes, RNA enzymes (ribozymes) can catalyze (start or accelerate) chemical reactions that are crit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Severe Acute Respiratory Syndrome
Severe acute respiratory syndrome (SARS) is a viral respiratory disease of zoonotic origin caused by the severe acute respiratory syndrome coronavirus (SARS-CoV or SARS-CoV-1), the first identified strain of the SARS coronavirus species, ''severe acute respiratory syndrome–related coronavirus'' (SARSr-CoV). The first known cases occurred in November 2002, and the syndrome caused the 2002–2004 SARS outbreak. In the 2010s, Chinese scientists traced the virus through the intermediary of Asian palm civets to cave-dwelling horseshoe bats in Xiyang Yi Ethnic Township, Yunnan.The locality was referred to be "a cave in Kunming" in earlier sources because the Xiyang Yi Ethnic Township is administratively part of Kunming, though 70 km apart. Xiyang was identified on * For an earlier interview of the researchers about the locality of the caves, see: SARS was a relatively rare disease; at the end of the epidemic in June 2003, the incidence was 8,469 cases with a case fatality rate (C ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coronaviridae
''Coronaviridae'' is a family of enveloped, positive-strand RNA viruses which infect amphibians, birds, and mammals. The group includes the subfamilies ''Letovirinae'' and ''Orthocoronavirinae;'' the members of the latter are known as coronaviruses. The viral genome is 26–32 kilobases in length. The particles are typically decorated with large (~20 nm), club- or petal-shaped surface projections (the "peplomers" or "spikes"), which in electron micrographs of spherical particles create an image reminiscent of the solar corona. Virology The 5' and 3' ends of the genome have a cap and poly(A) tract, respectively. The viral envelope, obtained by budding through membranes of the endoplasmic reticulum (ER) or Golgi apparatus, invariably contains two virus-specified glycoprotein species, known as the spike (S) and membrane (M) proteins. The spike protein makes up the large surface projections (sometimes known as peplomers), while the membrane protein is a triple-spanning t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reverse Transcriptase
A reverse transcriptase (RT) is an enzyme used to generate complementary DNA (cDNA) from an RNA template, a process termed reverse transcription. Reverse transcriptases are used by viruses such as HIV and hepatitis B to replicate their genomes, by retrotransposon mobile genetic elements to proliferate within the host genome, and by eukaryotic cells to extend the telomeres at the ends of their linear chromosomes. Contrary to a widely held belief, the process does not violate the flows of genetic information as described by the classical central dogma, as transfers of information from RNA to DNA are explicitly held possible. Retroviral RT has three sequential biochemical activities: RNA-dependent DNA polymerase activity, ribonuclease H (RNase H), and DNA-dependent DNA polymerase activity. Collectively, these activities enable the enzyme to convert single-stranded RNA into double-stranded cDNA. In retroviruses and retrotransposons, this cDNA can then integrate into the host genom ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Retrovirus
A retrovirus is a type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. Once inside the host cell's cytoplasm, the virus uses its own reverse transcriptase enzyme to produce DNA from its RNA genome, the reverse of the usual pattern, thus ''retro'' (backwards). The new DNA is then incorporated into the host cell genome by an integrase enzyme, at which point the retroviral DNA is referred to as a provirus. The host cell then treats the viral DNA as part of its own genome, transcribing and translating the viral genes along with the cell's own genes, producing the proteins required to assemble new copies of the virus. Although retroviruses have different subfamilies, they have three basic groups: the oncoretroviruses (oncogenic retroviruses), the lentiviruses (slow retroviruses) and the spumaviruses (foamy viruses). The oncoretroviruses are able to cause cancer in some species, the lentiviru ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Poliovirus
A poliovirus, the causative agent of polio (also known as poliomyelitis), is a serotype of the species ''Enterovirus C'', in the family of ''Picornaviridae''. There are three poliovirus serotypes: types 1, 2, and 3. Poliovirus is composed of an RNA genome and a protein capsid. The genome is a single-stranded positive-sense RNA (+ssRNA) genome that is about 7500 nucleotides long. The viral particle is about 30 nm in diameter with icosahedral symmetry. Because of its short genome and its simple composition—only RNA and a nonenveloped icosahedral protein coat that encapsulates it—poliovirus is widely regarded as the simplest significant virus. Poliovirus was first isolated in 1909 by Karl Landsteiner and Erwin Popper. The structure of the virus was first elucidated in 1958 using X-ray diffraction by a team at Birkbeck College led by Rosalind Franklin, showing the polio virus to have icosahedral symmetry. In 1981, the poliovirus genome was published by two different teams ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Positive-sense Single-stranded RNA Virus
Positive-strand RNA viruses (+ssRNA viruses) are a group of related viruses that have positive-sense, single-stranded genomes made of ribonucleic acid. The positive-sense genome can act as messenger RNA (mRNA) and can be directly translated into viral proteins by the host cell's ribosomes. Positive-strand RNA viruses encode an RNA-dependent RNA polymerase (RdRp) which is used during replication of the genome to synthesize a negative-sense antigenome that is then used as a template to create a new positive-sense viral genome. Positive-strand RNA viruses are divided between the phyla ''Kitrinoviricota'', ''Lenarviricota'', and ''Pisuviricota'' (specifically classes ''Pisoniviricetes'' and '' Stelpavirictes'') all of which are in the kingdom '' Orthornavirae'' and realm '' Riboviria''. They are monophyletic and descended from a common RNA virus ancestor. In the Baltimore classification system, +ssRNA viruses belong to Group IV. Positive-sense RNA viruses include pathogens s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Picornavirus
Picornaviruses are a group of related nonenveloped RNA viruses which infect vertebrates including fish, mammals, and birds. They are viruses that represent a large family of small, positive-sense, single-stranded RNA viruses with a 30 nm icosahedral capsid. The viruses in this family can cause a range of diseases including the common cold, poliomyelitis, meningitis, hepatitis, and paralysis. Picornaviruses constitute the family ''Picornaviridae'', order ''Picornavirales'', and realm '' Riboviria''. There are 158 species in this family, assigned to 68 genera. Notable examples are genera ''Enterovirus'' (including ''Rhinovirus'' and ''Poliovirus''), '' Aphthovirus'', ''Cardiovirus'', and ''Hepatovirus''. Etymology The name "picornavirus" has a dual etymology. Firstly, the name derives from ''picorna''- which is an acronym for "''p''oliovirus, ''i''nsensitivity to ether, ''c''oxsackievirus, ''o''rphan virus, ''r''hinovirus, and ribo''n''ucleic ''a''cid". Secondly, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Genetic Recombination
Genetic recombination (also known as genetic reshuffling) is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent. In eukaryotes, genetic recombination during meiosis can lead to a novel set of genetic information that can be further passed on from parents to offspring. Most recombination occurs naturally and can be classified into two types: (1) ''interchromosomal'' recombination, occurring through independent assortment of alleles whose loci are on different but homologous chromosomes (random orientation of pairs of homologous chromosomes in meiosis I); & (2) ''intrachromosomal'' recombination, occurring through crossing over. During meiosis in eukaryotes, genetic recombination involves the pairing of homologous chromosomes. This may be followed by information transfer between the chromosomes. The information transfer may occur without physical exchange (a se ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vertebrates
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with currently about 69,963 species described. Vertebrates comprise such groups as the following: * jawless fish, which include hagfish and lampreys * jawed vertebrates, which include: ** cartilaginous fish (sharks, rays, and ratfish) ** bony vertebrates, which include: *** ray-fins (the majority of living bony fish) *** lobe-fins, which include: **** coelacanths and lungfish **** tetrapods (limbed vertebrates) Extant vertebrates range in size from the frog species ''Paedophryne amauensis'', at as little as , to the blue whale, at up to . Vertebrates make up less than five percent of all described animal species; the rest are invertebrates, which lack vertebral columns. The vertebrates traditionally include the hagfish, which do no ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
