Circular RNA (or circRNA) is a type of single-stranded RNA which, unlike linear RNA, forms a covalently closed continuous loop. In circular RNA, the 3' and 5' ends normally present in an RNA molecule have been joined together. This feature confers numerous properties to circular RNA, many of which have only recently been identified.
Many types of circular RNA arise from otherwise protein-coding genes. Some circular RNA has been shown to code for proteins.[1][2] Some types of circular RNA have also recently shown potential as gene regulators. The biological function of most circular RNA is unclear.
Because circular RNA does not have 5' or 3' ends, it is resistant to exonuclease-mediated degradation and is presumably more stable than most linear RNA in cells.[3] Circular RNA has been linked to some diseases such as cancer.[4]
https://en.wikipedia.org/wiki/Circular_RNA
Viroids are small infectious pathogens.[1] They are composed solely of a short strand of circular, single-stranded RNA. Unlike viruses, they have no protein coating. All known viroids are inhabitants of angiosperms,[2]and most cause diseases, whose respective economic importance to humans varies widely.
https://en.wikipedia.org/wiki/Viroid
Non-cellular life, or acellular life is life that exists without a cellular structure for at least part of its life cycle.[1]Historically, most (descriptive) definitions of life postulated that a living organism must be composed of one or more cells,[2] but this is no longer considered necessary, and modern criteria allow for forms of life based on other structural arrangements.[3][4][5]
The primary candidates for non-cellular life are viruses. Some biologists consider viruses to be living organisms, but others do not. Their primary objection is that no known viruses are capable of autonomous reproduction: they must rely on cells to copy them.[1][6][7][8][9]
Engineers sometimes use the term "artificial life" to refer to software and robots inspired by biological processes, but these do not satisfy any biological definition of life.
https://en.wikipedia.org/wiki/Non-cellular_life
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; however, plasmids are sometimes present in archaea and eukaryotic organisms. In nature, plasmids often carry genes that benefit the survival of the organism and confer selective advantage such as antibiotic resistance. While chromosomes are large and contain all the essential genetic information for living under normal conditions, plasmids are usually very small and contain only additional genes that may be useful in certain situations or conditions. 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.[1][2][3]
https://en.wikipedia.org/wiki/Plasmid
Prions are misfolded proteins with the ability to transmit their misfolded shape onto normal variants of the same protein. They characterize several fatal and transmissible neurodegenerative diseasesin humans and many other animals.[3] It is not known what causes the normal protein to misfold, but the abnormal three-dimensional structure is suspected of conferring infectious properties, collapsing nearby protein molecules into the same shape. The word prion derives from "proteinaceous infectious particle".[4][5][6] The hypothesized role of a protein as an infectious agent stands in contrast to all other known infectious agents such as viroids, viruses, bacteria, fungi, and parasites, all of which contain nucleic acids (DNA, RNA, or both).
https://en.wikipedia.org/wiki/Prion
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.
https://en.wikipedia.org/wiki/RNA_world
| Circular satellite RNAs | |
|---|---|
Virus classification | |
| Informal group: | Satellite nucleic acids |
| Informal group: | Circular satellite RNAs |
Virusoids are circular single-stranded RNA(s) dependent on viruses for replication and encapsidation.[1] The genome of virusoids consist of several hundred (200–400) nucleotides and does not code for any proteins.
Virusoids are essentially viroids that have been encapsulated by a helper virus coat protein. They are thus similar to viroids in their means of replication (rolling circle replication) and in their lack of genes, but they differ in that viroids do not possess a protein coat. Both virusoids and viroids encode a hammerhead ribozyme.
Virusoids, while being studied in virology, are subviral particles rather than viruses. Since they depend on helper viruses, they are classified as satellites. Virusoids are listed in virological taxonomy as Satellites/Satellite nucleic acids/Subgroup 3: Circular satellite RNA(s).[2]
https://en.wikipedia.org/wiki/Virusoid
No comments:
Post a Comment