| nucleic acid | <biochemistry, molecular biology> Linear polymers of nucleotides, linked by 3', 5' phosphodiester linkages. In DNA, deoxyribonucleic acid, the sugar group is deoxyribose and the bases of the nucleotides adenine, guanine, thymine and cytosine. RNA, ribonucleic acid, has ribose as the sugar and uracil replaces thymine. DNA functions as a stable repository of genetic information in the form of base sequence. RNA has a similar function in some viruses but more usually serves as an informational intermediate (mRNA), a transporter of amino acids (tRNA), in a structural capacity or, in some newly discovered instances, as an enzyme. The spontaneous loss of the amino groups of cytosine (yielding uracil), methyl cytosine (yielding thymine) or of adenine (yielding hypoxanthine). It can be argued that the presence of thymine in DNA in place of the uracil of RNA stabilises genetic information against this lesion, since repair enzymes would restore the GU base pair to GC. (18 Nov 1997) |
|---|---|
| nucleic acid base | A purine or pyrimidine; found in naturally occurring nucleic acids such as DNA. (05 Mar 2000) |
| nucleic acid conformation | The characteristic 3-dimensional shape of a nucleic acid or polynucleotide. Its secondary structure is due to the formation of hydrogen bonds between nucleotides, resulting in base pairing and areas with alpha helix structure. (12 Dec 1998) |
| nucleic acid denaturation | Disorganization of secondary structures of nucleic acids through cleavage of hydrogen bonds and hydrophobic linkages. Denatured DNA appears to be a single-stranded flexible structure. The effects of denaturation on RNA are similar though less pronounced and largely reversible. (12 Dec 1998) |
| nucleic acid heteroduplexes | Double-stranded nucleic acid molecules (DNA-DNA or DNA-RNA) which contain regions of nucleotide mismatches (non-complementary). In vivo, these heteroduplexes can result from mutation or genetic recombination; in vitro, they are formed by nucleic acid hybridization. Electron microscopic analysis of the resulting heteroduplexes facilitates the mapping of regions of base sequence homology of nucleic acids. (12 Dec 1998) |
| nucleic acid hybridization | Widely used technique which exploits the ability of complementary sequences in single-stranded dnas or rnas to pair with each other to form a double helix. Hybridization can take place between two complimentary DNA sequences, between a single-stranded DNA and a complementary RNA, or between two RNA sequences. The technique is used to detect and isolate specific sequences, measure homology, or define other characteristics of one or both strands. (kendrew, encyclopedia of molecular biology, 1994, p503; dorlands, 28th ed, p781) (12 Dec 1998) |
| nucleic acid precursors | Use for nucleic acid precursors in general or for which there is no specific heading. (12 Dec 1998) |
| nucleic acid probe | A nucleic acid fragment, labelled by a radioisotope, biotin, etc., that is complementary to a sequence in another nucleic acid (fragment) and that will, by hydrogen binding to the latter, locate or identify it and be detected; a diagnostic technique based on the fact that every species of microbe possesses some unique nucleic acid sequences which differentiate it from all others, and thus can be used as identifying markers or "fingerprints." (05 Mar 2000) |
| nucleic acid probes | Nucleic acid which complements a specific mRNA or DNA molecule, or fragment thereof; used for hybridization studies in order to identify microorganisms and for genetic studies. (12 Dec 1998) |
| nucleic acid renaturation | The reformation of all, or part of, the native conformation of a nucleic acid molecule after the molecule has undergone denaturation. (12 Dec 1998) |
| nucleic acid synthesis inhibitors | Compounds that inhibit cell production of DNA or RNA. (12 Dec 1998) |
| nucleic acids | Highly complex portions of nucleoproteins that yield a mixture of purines and pyrimidines, a ribose or deoxyribose component, and phosphoric acid on complete hydrolysis. The two general types are ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). (12 Dec 1998) |
| nucleic acids, nucleotides, and nucleosides | Complex compounds of high molecular weight occurring in living cells. These are basically of two types, ribonucleic (RNA) and deoxyribonucleic (DNA) acids, both of which consist of nucleotides (nucleoside phosphates linked together by phosphate bridges). (12 Dec 1998) |
| regulatory sequences, nucleic acid | DNA sequences involved in regulating the expression of other genes. (12 Dec 1998) |
|---|---|
| repetitive sequences, nucleic acid | Nucleotide sequences present in multiple copies in the genome. They include direct, inverted, tandem, and terminal repeat sequences and the alu family repeat (named for the restriction endonuclease cleavage enzyme alu I). (12 Dec 1998) |
| minus-strand nucleic acid | <molecular biology> An RNA or DNA strand which has the opposite sense of (would be complementary to) the mRNA of a virus. (12 Jan 1998) |
| sequence homology, nucleic acid | The sequential correspondence of nucleotide triplets in a nucleic acid molecule which permits nucleic acid hybridization. Sequence homology is important in the study of mechanisms of oncogenesis and also as an indication of the evolutionary relatedness of different organisms. The concept includes viral homology. (12 Dec 1998) |
| in situ nucleic acid hybridization | <molecular biology> The use of a DNA or RNA probe to detect the complementary DNA sequence. (12 Dec 1998) |
| Rambourg's chromic acid-phosphotungstic acid stain | <technique> A stain for glycoproteins, used with an electron microscope, with which ultrathin tissue sections reveal complex carbohydrates in the same locations as shown by Rambourg's periodic acid-chromic methenamine-silver stain. (05 Mar 2000) |
| a1-acid glycoprotein | <biology> Plasma protein of mammals and birds, 38% carbohydrate. In humans a single chain glycoprotein of 39 kD. Increased levels are associated with inflammation, pregnancy and various diseases. (18 Nov 1997) |
| abscisic acid | <biochemistry> A lipid hormone that inhibits cell growth in plants, it is associated with fruit drop, leaf death and seed dormancy. It is synthesised in the plastids from carotenoids. This hormone helps plants deal with water loss, and its effects can be reversed with gibberellins. (06 May 1997) |
| abscisic acid 8'-hydroxylase | <enzyme> Catalyses conversion of abscisic acid to 8'-hydroxyabscisic acid, which rearranges to phaseic acid Registry number: EC 1.14.99.- Synonym: aba 8'-hydroxylase (26 Jun 1999) |
| acetic acid | <chemical> The acid most commonly associated with vinegar, it is the most commercially important organic acid and is used to manufacture a wide range of chemical products, such as plastics and Acetobacter but, except for making vinegar, is usually made through synthetic processes. Derivatives of acetic acid which may be formed by substitution reactions. Mono- and di-substituted, as well as, halogenated compounds have been synthesised. Experimentally, alpha- and n2- substituted acetic acids have been examined for their anti-inflammatory activity and effect on the central nervous system respectively. Additionally, limited exposure data has been collected on dibromo and dichloroacetic acids to determine whether they pose health effects. Synonym: ethanoic acid. (26 Jun 1999) |
| acetoacetic acid | CH3COCH2COOH;one of the ketone bodies, formed in excess and appearing in the urine in starvation or diabetes. Synonym: diacetic acid. (05 Mar 2000) |
| acetohydroxamic acid | C2H5NO2; N-Hydroxyacetamide;an inhibitor of urease, used as adjunctive therapy in chronic urea-splitting urinary infections. (05 Mar 2000) |
| acetrizoic acid | <chemical> A water-soluble, iodinated radiographic contrast medium, used as sodium acetrizoate in hysterosalpingography. Pharmacological action: contrast media. Chemical name: Benzoic acid, 3-(acetylamino)-2,4,6-triiodo- (12 Dec 1998) |
| acetylsalicylic acid | <drug> An odourless, white, slightly bitter drug used to reduce pain, fever, inflammation and sometimes to prevent blood clotting. Also called aspirin. Some people cannot tolerate it because it can cause stomach bleeding, however. It is soluble in both water and alcoholand melts at 132 to 136 degrees C. (06 May 1997) |
| acetyltannic acid | An astringent used for treatment of diarrhoea. Synonym: diacetyltannic acid, tannylacetate. (05 Mar 2000) |