All articles starting with P

Protoplasma

Protoplasma is an Austrian peer-reviewed cell biology journal founded in 1926, published by Springer Vienna, covering animal, fungal, and plant cell biology, with ISSN 0033-183X and a 2025 impact factor of 2.7.

Protoplasmic astrocyte

Protoplasmic astrocyte: the gray-matter astrocyte class (versus fibrous astrocytes), with fine perisynaptic processes ensheathing synapses, glutamate and potassium clearance, nonoverlapping domains covering up to 2 million synapses in humans.

Protoplast

Protoplast: a plant cell stripped of its cell wall (term from Hanstein, 1880). Isolated enzymatically since Cocking 1960; totipotent, used for transformation, fusion, CRISPR editing, and single-cell sequencing.

Sep 29, 2026

Protoplast isolation

Protoplast isolation is a plant cell biology technique that enzymatically strips the cell wall, yielding wall-less cells used for transient gene expression, CRISPR editing, and single-cell sequencing.

protoporphyrin IX

Protoporphyrin IX (PPIX) is a cyclic tetrapyrrole and the immediate precursor to heme, central to hemoglobin, myoglobin, and cytochromes, and a photosensitizer whose red fluorescence guides tumor surgery.

Protoporphyrinogen oxidase

Protoporphyrinogen oxidase (PPO, PPOX, EC 1.3.3.4) is a membrane-bound FAD enzyme catalyzing the six-electron oxidation of protoporphyrinogen IX to protoporphyrin IX, the last common step of heme and chlorophyll synthesis; target of diphenyl ether herbicides and, when deficient, cause of variegate porphyria.

Protopterus

Protopterus, African lungfish, genus of four air-breathing freshwater sarcopterygian species in sub-Saharan Africa; family Lepidosirenidae with Lepidosiren, sister group to tetrapods, known for mucus-cocoon aestivation and a 40 Gb genome.

Protoscience

Protoscience is a philosophy of science term for a research field that is not yet an established science but may become one, as when alchemy led to chemistry.

Protospacer adjacent motif

The protospacer adjacent motif (PAM) is a short DNA sequence, usually 2–5 nucleotides long, next to a CRISPR target that most CRISPR-Cas systems require for spacer acquisition and cleavage.

Protostar

A protostar is a mass of interstellar gas and dust collapsing to form a star, gathering mass through an accretion disk until hydrogen fusion can power it.

Protostome

Protostomia (protostomes) is the bilaterian animal clade of Ecdysozoa and Lophotrochozoa, about 97% of animal species, defined by blastopore-forms-mouth development and strongly supported by phylogenomics, unlike Deuterostomia.

Prototheca moriformis algal oil

Prototheca moriformis algal oil is a refined high-oleic edible oil made by fermenting the microalga Prototheca moriformis, developed by Corbion and recognized as safe in the US.

Protothecosis

Protothecosis, infection by Prototheca algae (achlorophyllous, Trebouxiophyceae), causing human cutaneous, bursal, and disseminated disease and bovine mastitis; first human case 1964; amphotericin B is the mainstay drug.

Prototype

A prototype is an early, tangible version of a product or system built to test ideas, expose flaws, and gather feedback before committing to full-scale production or development.

Prototype (video game)

Prototype (2009) is Radical Entertainment's open-world action game, published by Activision Blizzard for Xbox 360, PS3, and PC, starring shapeshifter Alex Mercer in virus-infected Manhattan, with consume/disguise mechanics and a 2015 Biohazard Bundle re-release.

Prototype 2

Prototype 2 is a 2012 open-world action game by Radical Entertainment and Activision, casting the player as soldier James Heller hunting Alex Mercer in a ruined New York.

Prototype Fast Breeder Reactor

The Prototype Fast Breeder Reactor (PFBR) is a 500 MWe sodium-cooled fast breeder reactor at Kalpakkam, Tamil Nadu, India, designed by IGCAR and built by BHAVINI.

Prototype Fast Reactor

The Prototype Fast Reactor (PFR) was a sodium-cooled fast reactor at Dounreay, Scotland, built by the UK Atomic Energy Authority and operated from 1974 to 1994.

Sep 29, 2026

Prototype filter

A prototype filter is a normalized low-pass filter with a 1 rad/s corner frequency and 1 Ω impedances, serving as the template for deriving practical low-pass, high-pass, band-pass, and band-stop filters.

Prototype-based programming

Prototype-based programming is a style of object-oriented programming in which objects reuse behavior by delegating to prototype objects instead of classes, as in JavaScript and Self.

Sep 29, 2026

Prototypical network

A prototypical network is a metric-based few-shot learning method that classifies examples by comparing their embeddings to one prototype per class, introduced by Snell, Swersky, and Zemel at NIPS 2017.

Prototypical networks

Prototypical networks are a metric-based meta-learning method for few-shot classification, introduced by Jake Snell, Kevin Swersky, and Richard Zemel at NIPS 2017, which classifies queries by distance to class prototypes.

Protozoa

Protozoa: heterotrophic single-celled eukaryotes that move and ingest food; not a valid taxon but a polyphyletic assemblage spanning amoebae, flagellates, ciliates, and sporozoa, including malaria parasites (282 million cases, 610,000 deaths in 2024).

Protozoan infection

Protozoan infection: disease caused by single-celled parasites such as Plasmodium, Giardia, Entamoeba, and Leishmania. Spread fecal-orally or by insect vectors; malaria causes about 610,000 deaths yearly; diagnosed by stool O&P tests and blood smears.