All articles starting with O
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Oligocene
The Oligocene, from 33.9 to 23.03 million years ago, is the youngest epoch of the Paleogene Period, marked by global cooling, Antarctic ice sheet growth, and major mammal turnovers.
Oligochaeta
Oligochaeta, the few-bristled annelid worms (non-leech Clitellata), includes earthworms and aquatic worms, about 5,000 species in ~30 families; paraphyletic without leeches, with eleven orders proposed in 2021.
Oligocone trichromacy
Oligocone trichromacy (oligocone syndrome, ORPHA:75378) is a rare congenital cone dysfunction disorder with reduced visual acuity, absent or reduced cone ERG, normal fundus and rod responses, and preserved color vision; some cases involve CNGA3, CNGB3, or PDE6C mutations.
Oligodendrocyte
Oligodendrocyte, also called oligodendroglia: CNS glial cell forming myelin sheaths around multiple axons (up to 1–40), unlike single-axon Schwann cells; arises from OPCs, supports axons metabolically, and enables remyelination in multiple sclerosis.
Oligodendrocyte precursor cell
Oligodendrocyte precursor cells (OPCs), also called NG2 glia or polydendrocytes, are CNS glia that generate myelinating oligodendrocytes, receive synaptic input, remodel synapses, support the blood-brain barrier, and drive remyelination in multiple sclerosis.
Oligodendroglioma
Oligodendroglioma, also known as an oligodendroglial tumor, is a brain tumor defined by an IDH mutation and 1p/19q codeletion, most common between ages 35 and 44 and often first causing seizures.
Oligodendroglioma grade 3
Oligodendroglioma grade 3 (formerly anaplastic oligodendroglioma) is a malignant IDH-mutant, 1p/19q-codeleted brain tumor; standard care is radiotherapy plus PCV chemotherapy, with temozolomide as a toxicity-sparing alternative.
Oligodon
Oligodon (kukri snakes), genus of colubrid snakes with 90 species across Asia, the second largest snake radiation; egg-eating specialists with blade-like rear teeth, eight species groups, late Oligocene origin in mainland Southeast Asia.
Oligodontia
Oligodontia, or selective tooth agenesis, is the congenital absence of six or more permanent teeth excluding third molars. Prevalence 1/625–1/1,250 in Europeans; caused by WNT10A, PAX9, and other genes, isolated or syndromic.
Oligodynamic effect
The oligodynamic effect, or oligodynamic action, is the biocidal action of trace metal ions against bacteria, fungi, and viruses, described by Carl von Nägeli in 1893.
Oligohydramnios
Oligohydramnios, low amniotic fluid volume in pregnancy, is diagnosed as AFI ≤5 cm or single deepest pocket <2 cm; causes include membrane rupture, placental insufficiency, and fetal urinary anomalies.
Oligohymenophorea
Oligohymenophorea (Holotricha, Oligohymenophora) is a class of ciliate protozoa in Ciliophora, established by de Puytorac et al. 1974, with seven subclasses, distinct oral ciliature, and model genera Tetrahymena and Paramecium.
Oligolectic bees
Oligolectic bees are bee species whose females gather pollen for their larvae from a narrow, related set of host plants, typically within a single plant family, unlike generalist bees.
Oligomeganephronia
Oligomeganephronia (oligomeganephronic renal hypoplasia) is a rare congenital kidney malformation with about 80% fewer nephrons and marked glomerular and tubular hypertrophy, causing childhood or adolescent renal failure, sometimes with PAX2 or chromosomal syndromes.
Oligomer
An oligomer is a molecule of intermediate molecular mass made of a few units from smaller molecules, sitting between small molecules and polymers, with two units forming a dimer.
Oligomycin
Oligomycin is a group of toxic macrolide antibiotics produced by Streptomyces that inhibits ATP synthase, and serves as a standard laboratory tool for measuring mitochondrial respiration.
Oligonucleotide
Oligonucleotide: a short synthetic nucleotide polymer (2-20 nt) used as probe, primer, or therapeutic; ASO, siRNA, aptamer, splice-switching drugs with phosphorothioate and 2' modifications, first approved 1998 (fomivirsen).
Oligonucleotide synthesis
Oligonucleotide synthesis is the chemical construction of short, defined-sequence single-stranded nucleic acids, typically 10 to a few hundred nucleotides long, without a biological template, dominated by automated solid-phase phosphoramidite chemistry.
Oligopeptide transporter
Oligopeptide transporter: integral membrane proteins moving short peptides across membranes, including the mammalian proton-coupled SLC15 family (PepT1, PepT2, PhT1, PhT2), the OPT family, and bacterial ABC oligopeptide importers.
Oligopoly
An oligopoly is a market structure in which a small number of large firms hold most of an industry's sales, as with Boeing and Airbus.
Oligopsony
Oligopsony is a market structure in which a small number of buyers face many sellers, giving buyers power to push prices or wages below competitive levels; it mirrors oligopoly.
Oligoryzomys
Oligoryzomys (pygmy rice rats, genus Oligoryzomys Bangs, 1900) is a Cricetidae rodent genus of about 22–24 species from Mexico to Argentina, with 2n 44–72, cryptic taxonomy, and hantavirus reservoir species such as O. longicaudatus.
Oligosaccharide
An oligosaccharide is a carbohydrate made of 2 to about 10 monosaccharide units joined by glycosidic bonds, found in human milk, seeds, and cell-surface glycoproteins and glycolipids.
Oligosaccharyltransferase
Oligosaccharyltransferase (OST; STT3A/STT3B complexes) is the ER membrane enzyme that transfers GlcNAc2Man9Glc3 from dolichol-PP onto Asn-X-Ser/Thr sequons, cotranslationally (STT3A) or posttranslationally (STT3B), causing CDG when defective.
Oligosaccharyltransferase complex subunit
Oligosaccharyltransferase complex subunit: any protein component of OST, the ER membrane enzyme that transfers Glc3Man9GlcNAc2 from dolichol to asparagine (N-linked glycosylation). Includes catalytic STT3A/STT3B, shared subunits RPN1, RPN2, DAD1, OST48, OST4, TMEM258, and isoform-specific DC2, KCP2, TUSC3, MAGT1.
Oligosaccharyltransferase complex subunit OSTC
OSTC (DC2), UniProt Q9NRP0, is a 149-aa non-catalytic subunit of the human STT3A oligosaccharyltransferase (OST-A) complex that, with KCP2, bridges STT3A to the Sec61 translocon for co-translational N-glycosylation; gene at 4q25.
Oligosaccharyltransferase insert domain
Oligosaccharyltransferase insert domain (OST_IS, InterPro IPR041530, Pfam PF18246): a beta-barrel-like domain inserted into the central core of the STT3/PglB/AglB N-glycosylation enzyme; function unknown, contains a disulphide bond.
Oligosoma
Oligosoma (Girard, 1857) is the genus of New Zealand skinks, family Scincidae, absorbing Cyclodina in 2009; about 56 endemic species, colonized NZ in the early Miocene, with many cryptic, threatened species.
Oligotrophication
Oligotrophication, also called re-oligotrophication, is the decline of nutrient concentrations and productivity in an aquatic ecosystem, most often a deliberate result of cutting nitrogen and phosphorus inputs to a formerly eutrophic lake.
Oliguria
Oliguria, also called low urine output, is urine production below 500 mL/24h or 0.5 mL/kg/hour. It is a KDIGO criterion for acute kidney injury staging, with prerenal, renal, and postrenal causes.