| 释义 |
plectonemic, a. Biol.|plɛktəʊˈniːmɪk|
[f. Gr. πλεκτός twisted + νῆµα thread + -ic.]
Of, pertaining to, or designating two or more like helices coiled together side by side in such a way that they cannot be fully separated unless they are unwound. Opp. paranemic a.
1941A. H. Sparrow et al. in Canad. Jrnl. Res. C. XIX. 325 Kuwada..describes two types of double-stranded spirals: (1) orthospirals, which are formed when the two threads being coiled have one end free so that internal twisting does not occur; (2) anorthospirals, which result when two strands with both ends fixed are coiled together and in consequence have a twist compensating for each gyre of the spiral... Orthospirals are interlocked and cannot be separated without untwisting; anorthospirals are independent and can readily be pulled apart or fitted into each other... The term ‘paranemic’ (para = beside) instead of anorthospiral will be used here since it is simpler and its implications are clear. Instead of orthospiral ‘plectonemic’ (plektos = twisted) will be used as this has the advantage of indicating the relationship of the strands. 1950[see paranemic a.]. 1953Watson & Crick in Cold Spring Harbor Symp. Quant. Biol. XVIII. 129/2 We therefore believe that if a helical structure is present [in DNA], the relationship between the helices will be plectonemic. 1971Nature 22 Jan. 241/1 Tropocollagen..consists of three protein chains with similar, specific and very characteristic amino-acid compositions, twisted into a plectonemic triple helix of about 100 turns. 1974[see paranemic a.].
Hence plectoˈnemically adv.
1953Cold Spring Harbor Symp. Quantitative Biol. XVIII. 128/2 Apart from breaking the chains there are only two sorts of ways to separate two chains coiled plectonemically. 1966Mahler & Cordes Biol. Chem. iv. 140 DNA in its B lattice configuration..consists of two right-handed helical polynucleotide chains of opposite polarity, plectonemically coiled around the same axis to form a double helix. 1979Nature 26 Apr. 780/3 Sasisekharan et al...have..proposed that the two strands of DNA do not coil plectonemically round one another. |