| mannich bases | Ketonic amines prepared from the condensation of a ketone with formaldehyde and ammonia or a primary or secondary amine. A mannich base can act as the equivalent of an alpha,beta unsaturated ketone in synthesis or can be reduced to form physiologically active amino alcohols. (12 Dec 1998) |
|---|---|
| schiff bases | Condensation products of aromatic amines and aldehydes forming azomethines substituted on the n atom, containing the general formula r-n:chr. (12 Dec 1998) |
| histone bases | The alpha-amino acids arginine, histidine, and lysine, which are basic by virtue of the presence in the side chains of a guanidine, imidazole, and amine group, respectively; the term "hexone" is a misnomer since histidine does not have six carbons. (05 Mar 2000) |
| denture bases | The part of a denture that overlies the soft tissue and supports the supplied teeth and is supported in turn by abutment teeth or the residual alveolar ridge. It is usually made of resins or metal or their combination. (12 Dec 1998) |
| ointment bases | Various mixtures of fats, waxes, animal and plant oils and solid and liquid hydrocarbons; vehicles for medicinal substances intended for external application; there are four classes: hydrocarbon base, absorption base, water-removable base and water-soluble base; several are also emollients. (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) |
| 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) |