| r | Commonly used abbreviation for respiration(s). For example, in a medical chart, you might see scrawled bp90/60 t98.6 hr 60/reg r15 , which is short hand signifying that the blood pressure is 90/60 mm hg, the temperature (t) is 98.6 degrees fahrenheit, the heart rate (hr) is 60/min and regular, and the respirations (r) 15/min. (this example would be entirely normal for an adult or older child). Symbol for a ring chromosome, a structurally abnormal chromosome in which the end of each chromosome arm has been lost and the broken arms have been reunited in ring formation. (12 Dec 1998) |
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| R antigen | Those that produce active haemolysins (O and S) which cause a zone of clear haemolysis on the blood agar medium in the area of the colony; beta-haemolytic streptococci are divided into groups (A to O) on the basis of cell wall C carbohydrate (see Lancefield classification); Group A (in the strains pathogenic for man) comprises more than 50 types (designated by Arabic numerals) determined by cell wall M protein, which seems to be associated closely with virulence and is produced chiefly by strains with matt or mucoid colonies, in contrast to nonvirulent, glossy colony-producing strains; other surface protein antigens such as R and T (T substance), and the nucleoprotein fraction (P substance) seem to be of less importance. The more than 20 extracellular substances elaborated by strains of beta-haemolytic streptococci include erythrogenic toxin (elaborated only by lysogenic strains), deoxyribonuclease (streptodornase), haemolysins (streptolysins O and S), hyaluronidase, and streptokinase. Synonym: haemolytic streptococci. (05 Mar 2000) |
| R body | <biology, microbiology> A protein structure, visible by optical microscopy, found in various bacteria, probably related to plasmid presence. Found both in free living pseudomonads and in various bacteria endosymbiotic in Paramecium. Has toxic activity against Paramecium and confers killer characteristics on Paramecium that ingest bacteria containing the structure. (18 Nov 1997) |
| R enzyme | <enzyme> An enzyme with action similar to that of isoamylase; it cleaves 1,6-alpha-glucosidic linkages in pullalan, amylopectin, and glycogen, and in alpha-and beta-amylase limit-dextrins of amylopectin and glycogen. Compare: isoamylase. Synonym: limit dextrinase, pullulanase, R enzyme. (05 Mar 2000) |
| r factors | A class of plasmids that transfer antibiotic resistance from one bacterium to another by conjugation. (12 Dec 1998) |
| r group | <chemistry> A chemical abbreviation that normally denotes an alkyl group, but is occasionally used to refer to other organic groups. (09 Oct 1997) |
| R loop | <molecular biology> A single stranded loop section of DNA formed by the association of a section of ssRNA with the other strand of the DNA in this region whereby one DNA strand is displaced as the loop. Mature mRNA can be used to form loops from exons with the intervening double stranded linear regions being introns. (23 Aug 1998) |
| R plasmid | <molecular biology> A plasmid that confers resistance to one or more antibiotics or other poisonous compounds in a bacterium. (17 Dec 1997) |
| R plasmids | Plasmid's carrying genes responsible for antibiotic (or antibacterial drug) resistance among bacteria (notably Enterobacteriaceae); they may be conjugative or nonconjugative plasmid's, the former possessing transfer genes (resistance transfer factor) lacking in the latter. Synonym: R factors, R plasmids, resistance factors, resistance-transferring episomes. (05 Mar 2000) |
| R recombinase | <enzyme> From zygosaccharomyces rouxii; a yeast site-specific recombinase Registry number: EC 2.7.7.- Synonym: arg recombinase, r protein (26 Jun 1999) |
| R wave | The first positive (upward) deflection of the QRS complex in the electrocardiogram; successive upward deflections within the same QRS complex are labelled R', R'', etc. (05 Mar 2000) |
| R-banding | See: R-banding stain. (05 Mar 2000) |
| R-banding stain | <technique> A reverse Giemsa chromosome banding method that produces bands complementary to G-bands; induced by treatment with high temperature, low pH, or acridine orange staining; often used together with G-banding on human karyotype to determine whether there are deletions. (05 Mar 2000) |
| R-on-T phenomenon | A premature ventricular (QRS) complex in the electrocardiogram interrupting the T wave of the preceding beat; often predisposes to serious ventricular arrhythmias. (05 Mar 2000) |
| R-R interval | The time elapsing between two consecutive R waves in the electrocardiogram. (05 Mar 2000) |