A very small piece or portion of anything. [L. particula, dim. of pars, part]
alpha p. (a) a p. consisting of two neutrons and two protons, with a positive charge (2e+); emitted energetically from the nuclei of unstable isotopes of high atomic number (elements of mass number from 82 up); identical to the helium nucleus.alpha ray;
beta p. an electron, either positively (positron, beta+) or negatively (negatron, beta-) charged, emitted during beta decay of a radionuclide. See also cathode rays, under ray.beta ray;
chromatin p.'s fine bluish dots thought to represent remnants of the nucleus, occasionally seen in stained erythrocytes.
core p. p. released by partial enzymatic digestion of chromatin.
Dane p.'s the larger spherical forms of hepatitis-associated antigens; they comprise the virion of hepatitis B virus, containing a 27-nm "core" in which DNA-dependent DNA polymerase and circular, double-stranded DNA have been found.
defective interfering p. an incomplete virus that is unable to replicate and interferes with replication of an infectious virus.
D.I. p. abbreviation for defective interfering p.
electron transport p.'s (ETP) fragments of mitochondria still capable of transporting electrons.submitochondrial p.'s;
elementary p. 1. platelet 2. one of the units occurring on the matrical surface of mitochondrial cristae; the head of the p., which measures about 9 nm, attaches to the membrane of the crista by a stalk 5 nm in length; the p.'s may be concerned with the electron transport system.
kappa p.'s inheritable cytoplasmic symbionts, once thought to be p.'s mainly or exclusively of DNA, occurring in some strains of Paramecium; capable of producing a product lethal to other strains.
signal recognition p. (SRP) a small RNA-protein complex that interacts with the signal sequence of nascent secretory proteins. Binding of the signal recognition p. results in arrest of translation until interaction with docking protein, an integral part of the endoplasmic reticulum membrane.
submitochondrial p.'s electron transport p.'s
Zimmermann's elementary p. platelet
Browse Medical References: