Microbiology terms - P
- palindrome
- A nucleotide sequence on a DNA molecule in which the same sequence is
found on each strand, but in the opposite direction.
- pandemic
- A worldwide epidemic.
- parasite
- An organism able to live on and cause damage to another organism.
- passive immunity
- Immunity resulting from transfer of antibodies or immune cells from an
immune to a nonimmune individual. Compare with active immunity
- pasteurization
- A process using mild heat to reduce the microbial level in heat-sensitive
materials.
- pathogen
- An organism able to inflict damage on a host it infects.
- pathogenicity
- The ability of a parasite to inflict damage on the host.
- pellicle
- A relatively rigid layer of proteinaceous elements just beneath the plasma
membrane in many protozoa and algae. The plasma membrane is sometimes
considered part of the pellicle.
- peptide bond
- A type of covalent bond joining amino acids in a polypeptide.
- peptidoglycan
- The rigid layer of the cell walls of Bacteria, a thin sheet composed of
N-acetylglucosamine, N-acetylmuramic acid, and a few amino acids. Also
called murein.
- periplasmic space
- The area between the cytoplasmic membrane and the cell wall in
gram-negative Bacteria, containing certain enzymes involved in nutrition.
- peritrichous flagellation
- Having flagella attached to many places on the cell surface.
- person to person epidemic
- An epidemic resulting from person to person contact, characterized by a
gradual rise and fall in number of cases.
- PFU
- Stands for plaque-forming unit.
- phage
- See bacteriophage.
- phagemid
- A cloning vector that can replicate either as a plasmid or as a bacteriophage.
- phagocyte
- A body cell able to ingest and digest foreign particles.
- phagocytosis
- Ingestion of particulate material such as bacteria by protozoa and phagocytic
cells of higher organisms.
- phenotype
- The observable properties of an organism. Compare with genotype.
- phosphodiester bond
- A type of covalent bond linking nucleotides together in a polynucleotide.
- phospholipid
- Lipids containing a substituted phosphate group and two fatty acid chains on
a glycerol backbone.
- photoautotroph
- An organism able to use light as its sole source of energy and carbon dioxide
as sole carbon source.
- photohetrotroph
- An organism using light as a source of energy and organic materials as
carbon source.
- photophosphorylation
- Synthesis of high-energy phosphate bonds as ATP, using light energy.
- photosynthesis
- The process of using the light energy to synthesize carbohydrates from
carbon dioxide (CO2). In general, photosynthesis can be summaried by the
equation:
CO2 + 2 H2O --> [CH2O] + H2O + O2
See also anoxygenic photosynthesis and oxygenic photosynthesis.
- phototaxis
- Movement toward light.
- phototroph
- In reference to energy source - an organism which uses light as the energy
source to drive the electron flow from the elctron donors (e.g. water,
hydrogen sulfide). Compare with autotroph, lithotroph, heterotroph,
organotroph.
- phycobilin
- Also phycobiliprotein or biliprotein. A water-soluble pigment which occurs
in cyanobacteria and functions as the light-harvesting pigments for
phytosystem II.
- phylogeny
- The ordering of species into higher taxa and the construction of evolutionary
trees based on evolutionary (natural) relationships.
- phytanyl
- A branched-chain hydrocarbon containing 20 carbon atoms, commonly
found in the lipids of Archaea.
- pilus (plural pili)
- A fimbria-like structure that is present on fertile cells, both Hfr and F+, and
is involved in DNA transfer during conjugation. Sometimes called sex pilus.
See also fimbria.
- pinocytosis
- In eukaryotes, phagocytosis of soluble molecules.
- plaque
- A localized area of clearing in a bacterial lawn on an agar plate. The clearing
is due to lysis or inhibited growth of cells which is caused by virus or
bacteriophage infection.
- plaque-forming unit
- Abbreviated as pfu. Refer to any entity which can give rise to a plaque. For
example, if a phage stock solution has 1010 pfu/ml, it means that every ml of
this stock has 1010 phage particles which can form plaques. This
(pfu/ml) is the conventional way to refer the concentration of a phage
preparation. Compare with CFU.
- plasma
- The noncellular portion of blood.
- plasma cell
- A large differentiated and short-lived B lymphocyte specializing in abundant
(but short term) anitbody production.
- plasma membrane
- See cytoplasmic membrane.
- plasmid
- An extrachromosomal genetic element not essential for growth and which
has no extracellular form.
- platelet
- A noncellular disc-shaped structure containing protoplasm found in large
numbers in blood and functioning in the blood clotting process.
- plus-strand nucleic acid
- An RNA or DNA strand which has the same sense as the mRNA of a virus.
- polar
- Possessing hydrophilic characteristics and generally water soluble.
- polar flagellation
- Condition of having flagella attached at one end or both ends of the cell.
- poly-beta-hydroxybutyrate (PHB)
- A common storage material of prokaryotic cells consisting of a polymer of
beta-hydroxybutyrate (PHB) or other beta-alkanoic acids. (PHA).
- polyclonal antiserum
- A mixture of antibodies to a variety of antigens or to a variety of
determinants on a single antigen.
- polymer
- A large molecule formed by polymerization of monomeric units.
- polymerase chain reaction (PCR)
- A method for amplifying DNA in vitro, involving the use of oligonucleotide
primers complementary to nucleotide sequences in a target gene and the
copying of the target sequences by the action of DNA polymerase.
- polymorphonuclear leukocyte (PMN)
- Small, actively motile white blood cells containing many lysosomes and
specializing in phagocytosis.
- polynucleotide
- A polymer of nucleotides bonded to one another by phosphodiester bonds.
- polypeptide
- Several amino acids linked together by peptide bonds
- polysaccharide
- A long chain of monosaccharides (sugars) linked by glycosidic bonds.
- porin
- A rotein channel in the lipopolysaccharide layer of gram-negative bacteria.
- porphin
- A cyclic tetrapyrrole in which the four pyrrole groups are linked by their
alpha-carbon atoms via methene (-CH=) bridges; porphin is the partial
compund of porphyrins.
- porphyrin
- A porphin derivatives in which the pyrrole beta-carbons are variously
substitued. Porphyrin can readily chelate vrious metals, the
metalloporphyrins being components of several important biological
pigments, e.g. chlorophylls, cytochromes, haem.
- porter
- A membrane protein that functions to transport substances into and out of
the cell.
- precipitation
- A reaction between antibody and soluble antigen resulting in a visible mass
of antibody-antigen complexes.
- prevalence
- The proportion of individuals in a population having a disease.
- Pribnow box
- The consensus sequence TATAAT located approximately 10 base pairs
upstream from the transcriptional start site.
- primary antibody response
- Antibodies made upon first exposure to antigen; mostly of the class IgM.
- primary metabolite
- A metabolite excreted during the growth phase.
- primary producer
- An organism that uses light to synthesize new organic material from carbon
dioxide.
- primary structure
- In an informational macromolecule, such as a polypeptide or a nucleic acid,
the pricise sequence of monomeric units.
- primary transcript
- An unprocessed RNA molecule which is the direct product of transcription.
- primer
- A molecule (usually a polynucleotide) to which DNA polymerase can attach
the first nucleotide during DNA replication.
- prion
- Derived from "proteinaceous infectious particle"; an infectious agent whose
extracellular form consists entirely of protein and without any nucleic acid.
The causal agent of the sheep/goats disease "scrapie". Compare with virion
and virus.
- probe
- See nucleic acid probe.
- prochlorophyte
- A prokaryotic oxygenic phototroph that contains chlorophylls a and b but
which lack phycobilins.
- prokaryote
- A cell or organism lacking a unit membrane-bound (true) nucleus and other
organelles, usually having its DNA in a single circular molecule.
- promoter
- The site on DNA where the RNA polymerase binds and begins
transcription.
- prophage
- The state of the genome of a temperate virus when it is replicating in
synchrony with that of the host, typically integrated into the host genome.
- prophylactic
- Treatment, usually immunologic or chemotherapeutic, designed to protect an
individual from a future attack by a pathogen.
- prosthecae
- A cytoplasmic extrusion often forming a distinct appendage, bounded by the
cell wall such as a bud, hypha. or stalk.
- prosthetic group
- The tightly bound, nonprotein portion of an enzyme; not the same as
coenzyme.
- protein
- A polymeric molecule consisting of one or more polypeptides
- proton motive force (PMF)
- An energized state of a membrane created by expulsion of protons through
action of an electron transport chain. See also chemiosmosis.
- protoplasm
- The complete cellular contents, cytoplasmic membrane, cytoplasm, and
nucleus; usually considered to be the living portion of the cell, thus excluding
those layers peripheral to the cytoplasmic membrane.
- protoplast
- A cell from which the wall has been removed.
- prototroph
- The parent from which an auxotrophic mutant has been derived. Contrast
with auxotroph.
- protist
- A member of the Protista.
- Protista
- 1. A taxon (kingdom) which includes the algae, fungi and protozoa
(collectively, the eukaryotic protists), and the prokaryotes.
2. A kingdom comprising the eukaryotic protists.
- protozoa
- Unicellular eukaryotic microorganisms that lack cell walls.
- provirus
- See prophage.
- pseudomonad
- Member of the genus Pseudomonas, a large group of gram-negative,
obligately respiratory (never fermentative) Bacteria.
- pseudopodium (plural: pseudopodia)
- The protrusion of an amoeboid cell formed by the extrusion or streaming of
the cytoplasm (but still enclosed in the membrane) for the purpose of
movement or feeding.
- psychrophile
- An organism able to grow at low temperatures and showing a growth
temperature optimum of <15 C.
- psychrotolerant
- An organism able to grow at low temperature but having a growth
temperature optimum of > 15 °C.
- public health
- The health of the population as a whole.
- pure culture
- A culture containing a single kind of microorganism.
- purple sulfur bacteria
- A group of phototrophic prokaryotes containing bacteriochlorophylls a or b
and characterized by the ability to oxideze hydrogen sulfide (H2S) and store
elemental sulfur inside the cells.
- pyogenic
- Pus-forming; causing abscesses.
- pyrite
- A common iron ore. FeS2.
- pyrogenic
- Fever-inducing.
- pus
- A viscous, yellowish-white fluid formed in infected tissue, consisting chiefly
of leukocytes, cellular debris, and liquified tissue elements.
Compiled by Tsute Chen, Converted by Ben Hoyt