Cell biology

Organelle

Organelle: membrane-surrounded subcellular structure with a specific function, such as the nucleus, mitochondria, lysosomes, ER, Golgi, and peroxisomes; eukaryotic cells compartmentalize nearly half their volume in organelles, unlike prokaryotes.

Organoid culture

Organoid culture is a cell culture method in which stem cells grown in a three-dimensional matrix self-organize into miniature organ-like structures used to study development and disease.

Organotypic culture

Organotypic culture is a cell culture method that grows cells or tissue in three dimensions, preserving the architecture and cell-type diversity of the original tissue.

Organotypic slice culture

Organotypic slice culture is a bench biology technique that keeps thin tissue slices, most often brain, alive for weeks to months while preserving their 3D architecture and synaptic connections.

Origin and function of meiosis

Origin and function of meiosis: meiosis evolved from mitosis in early eukaryotes, was present in the LECA, uses archaeal-derived Spo11 machinery, and functions in DNA restoration, disjunction, and recombination.

OS-RC-2

OS-RC-2 (OSRC2, RC-2, CVCL_1626) is a human clear cell renal cell carcinoma cell line established in 1985 from a 52-year-old Japanese male; VHL-null, 3p-deleted, ccB subtype, sorafenib-resistant, used in RCC drug-resistance and metastasis research.

Osteoprotegerin

Osteoprotegerin (OPG, TNFRSF11B, OCIF) is a secreted TNF receptor superfamily decoy receptor that binds RANKL to block osteoclast formation, protecting bone mass; mutations cause juvenile Paget's disease.

OVCAR-3

OVCAR-3 (NIH:OVCAR-3, ATCC HTB-161, CVCL_0465) is a human high-grade serous ovarian adenocarcinoma cell line established in 1982 from malignant ascites of a 60-year-old woman; cisplatin-resistant, hormone-receptor positive, NCI-60 member.

OVCAR-5

OVCAR-5 (NIH:OVCAR-5, CVCL_1628) is a human cancer cell line from the ascites of a 67-year-old untreated patient, registered as high-grade ovarian serous adenocarcinoma but suspected of upper gastrointestinal origin; NCI-60 member with homozygous KRAS Gly12Val.

OVCAR-8

OVCAR-8 (NIH:OVCAR-8, CVCL_1629) is a human ovarian cancer cell line from a 64-year-old donor, a member of the NCI-60 panel, TP53-mutant, hyperdiploid, and the only HGSOC line tested that reliably forms ascites in nude mice.

Oxidative damage and mitochondrial dysfunction in ageing

Oxidative damage and mitochondrial dysfunction in aging is the lifetime accumulation of oxidative lesions in mitochondrial DNA, respiratory-chain proteins, and membrane lipids, causing declining respiratory capacity in aged tissues.

Oxidative stress

Oxidative stress, also called oxidant stress, is an imbalance between oxidants and antioxidants that disturbs cell signaling and causes damage; Helmut Sies coined the term in 1985.

Oxysterol-binding protein

Oxysterol-binding protein (OSBP), founder of the ORP/OSBPL family, is a eukaryotic lipid transfer protein exchanging ER cholesterol for Golgi PI4P at membrane contact sites; humans have 12 ORP genes, yeast seven OSH genes.

P-site

The P-site (peptidyl site) is the ribosomal binding site for peptidyl-tRNA, the tRNA carrying the growing polypeptide chain; the initiator tRNA starts there each elongation cycle.

Oct 20, 2026

Pal1 cell morphology

Pal1 (Pal1p, YDR348c) is a fungal membrane-associated cell-polarity and early endocytic coat protein; its deletion makes fission yeast pear-shaped or spherical and Candida albicans pseudohyphal, distinct from PalI/Rim9 pH sensing and Pals1.

Panc 03.27

Panc 03.27, also written Panc 3.27 or PL11, is a human pancreatic adenocarcinoma cell line isolated in 1995 and distributed by ATCC as CRL-2549 for cancer research.

Panc 04.03

Panc 04.03 (CVCL_1636, ATCC CRL-2555) is a human pancreatic ductal adenocarcinoma cell line from a 70-year-old male, derived at Johns Hopkins, carrying KRAS G12D and TP53 G245S mutations, used in migration, drug, and radiotherapy studies.

PANC-1

PANC-1 (Panc-1, CVCL_0480, ATCC CRL-1469) is a human pancreatic ductal adenocarcinoma cell line from a 56-year-old male, reported 1975, carrying KRAS G12D, TP53 R273H, and CDKN2A deletion.

Pancreatic A cell

Pancreatic A cell, also called pancreatic alpha cell (CL:0000171), is a peripheral islet of Langerhans endocrine cell secreting glucagon, a 29-amino acid hormone opposing insulin; electrically excitable, amino-acid sensing, and dysregulated in diabetes.

Pancreatic endocrine cell

Pancreatic endocrine cells, the hormone-secreting cells of the islets of Langerhans, comprise five types: alpha (glucagon), beta (insulin), delta (somatostatin), gamma/PP (pancreatic polypeptide), and epsilon (ghrelin) cells.

Pancreatic stellate cell

Pancreatic stellate cell (PSC), vitamin A-storing pancreatic cell identified 1982, isolated 1998; quiescent in health, activated to myofibroblast-like ECM-producing cells driving fibrosis in chronic pancreatitis and pancreatic cancer stroma.

Paneth cell

Paneth cell: secretory epithelial cell at the base of small intestinal crypts of Lieberkühn; secretes α-defensins (HD5/HD6), lysozyme, and Reg3 lectins, supports intestinal stem cells, and is linked to ileal Crohn's disease via NOD2 and ATG16L1.

Oct 20, 2026

Pannexin

Pannexins (Panx1, Panx2, Panx3), vertebrate innexin homologs discovered in 2000, are single-membrane heptameric large-pore channels that release ATP and drive purinergic signaling, inflammation, and cell death.

Paraflagellar rod

Paraflagellar rod (PFR), or paraxial rod: lattice-like extra-axonemal filament alongside the flagellar axoneme of kinetoplastids, euglenoids, and dinoflagellates; built from PFR1 and PFR2, essential for trypanosome motility and viability.

Parafollicular cell

Parafollicular cell (thyroid C cell): endocrine thyroid cell secreting calcitonin, which lowers serum calcium. Originates from pharyngeal endoderm via the ultimobranchial body, not neural crest; source of medullary thyroid carcinoma.

Paraspeckle

Paraspeckles are mammalian nuclear bodies built on the NEAT1 long noncoding RNA and DBHS proteins SFPQ, NONO, and PSPC1; discovered in 2002, they regulate gene expression by RNA retention and protein sequestration, and are stress-responsive condensates linked to cancer and ALS.

Parietal cell

Parietal cells, also called oxyntic cells, are stomach epithelial cells that secrete hydrochloric acid, lowering gastric pH to 0.8, and intrinsic factor for vitamin B12 absorption.

Passive transport

Passive transport: movement of substances across cell membranes down concentration gradients without cell energy, including simple diffusion, facilitated diffusion via channels and carriers, osmosis, and filtration.

Patch clamp

Patch clamp: electrophysiology technique by Erwin Neher and Bert Sakmann (1976) using a gigaohm-sealed glass pipette to record single ion channel currents; configurations include cell-attached, whole-cell, inside-out, outside-out; 1991 Nobel Prize; now automated in 384-well high-throughput platforms.