| p | 1. Symbol for peta-; phosphorus; pressure or partial pressure; proline; product; power; frequently with subscripts indicating location and/or chemical species. 2. Followed by a subscript, 1) refers to the plasma concentration of the substance indicated by the subscript; 2) permeability constant. 3. A blood group designation. 4. Symbol for probability; when followed by the sign for "less than" (<) this indicates that a test statistic, e.g., a chi-square test gives a result unlikely to occur by chance. 5. <abbreviation> Pupil; optic papilla. 6. In polynucleotide symbolism, phosphoric ester or phosphate. 7. Symbol for pico-; momentum (in italics). 8. In cytogenetics, symbol for the short arm of a chromosome. Origin: fr. Fr. Petit, small (05 Mar 2000) |
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| P and P test | A test formerly used by some to control anticoagulant therapy with bishydroxycoumarin and indandione drugs. Synonym: P and P test. (05 Mar 2000) |
| P antigen | <haematology, immunology> Antigenic determinant on the surface of human red blood cells to which the Donath Landsteiner antibody reacts. This antibody binds in the cold (a cold IgG), but elutes from red cells at 37쵣, is particularly associated with tertiary syphylis and its binding causes paroxysmal nocturnal haemoglobinuria. (18 Nov 1997) |
| p arm of a chromosome | The short arm of a chromosome (from the french petit meaning small). All human chromosomes have 2 arms: the p and q arms. (12 Dec 1998) |
| p blood-group system | A blood group related to the abo, lewis and I systems. at least five different erythrocyte antigens are possible, some very rare, others almost universal. Multiple alleles are involved in this blood group. (12 Dec 1998) |
| P cell | A characteristic specialised cell, with probable pacemaker function, found in the S-A node and A-V junction. (05 Mar 2000) |
| P element | <molecular biology> A class of Drosophila transposon, widely used as a vector for reporter genes, for efficient germ line transformation and for enhancer trap or insertional mutagenesis studies. (18 Nov 1997) |
| P elements | A class of transposable elements in Drosophila responsible for hybrid dysgenesis; utilised as tools for introducing genes into new locations in the genome. (05 Mar 2000) |
| P enzyme | <enzyme> Enzyme that catalyses the sequential removal of glycosyl residues from glycogen to yield one glucose-1-phosphate per reaction. Its activity is controlled by phosphorylation (by phosphorylase kinase). (21 Jun 2000) |
| P face | Method of specimen preparation for the electron microscope in which rapidly frozen tissue is cracked so as to produce a fracture plane through the specimen. The surface of the fracture plane is then shadowed by heavy metal vapour, strengthened by a carbon film and the underlying specimen is digested away, leaving a replica that can be picked up on a grid and examined in the transmission electron microscope. The great advantage of the method is that the fracture plane tends to pass along the centre of lipid bilayers and it is therefore possible to get en face views of membranes that reveal the pattern of Integral membrane proteins. The E face is the outer lamella of the plasma membrane viewed as if from within the cell, the P face the inner lamella viewed from outside the cell. Fracture planes also often pass along lines of weakness such as the interface between cytoplasm and membrane, so that outer and inner membrane surfaces can be viewed. Further information about the structure can be revealed by freeze etching. Extremely rapid freezing followed by deep etching has allowed the structure of the cytoplasm to be studied without the artefacts that might be introduced by fixation. (18 Nov 1997) |
| p in biochemistry | The abbreviation for protein. For example, p53 is a protein (53 kilodaltons in size). (12 Dec 1998) |
| p in population genetics | The frequency of the more common of two different alternative (allelic) versions of a gene. (the frequency of less common allele is q). (12 Dec 1998) |
| P light chain | <protein> Myosin light chain that can be phosphorylated by myosin light chain kinase, as a result of phosphorylation, the myosin is activated. (18 Nov 1997) |
| P loop | See: ATP binding site. (18 Nov 1997) |
| P protein | <protein> Protein found in large amounts in phloem seive tubes. Appears as thin strands when seen in the electron microscope. (18 Nov 1997) |