A, BandZ develops ofthe DNA moleculeIn the deoxyribonucleic acid (DNA) molecule various combinations ofmonomeric compounds— nucleotides— connected together inalong chain are provided toencode the information about the framework ofproteins. Two chains ofdeoxyribonucleotides connect with every other adhering to acertain rule— the rule ofcomplementarity (adenine creates hydrogen bonds and also pairs with thymine and also guanine with cytosine) toform adouble helix. The resulting molecule deserve to beextremely long. Atthe human cells nuclei 2meters ofDNA isstored inavolume of40cubic micrometers (1).

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DNA structure indifferent forms

The DNA molecule exist indifferent forms under various conditions. The ordinary type ofDNA, theB form, predominates inthe cell. B-DNA nitrogenous bases are virtually perpendicular tothe helical axis, and each basic pair istwisted 36degrees loved one tothe surrounding bases. Each complete turn ofthe helix includes 3.4nm or10base bag (9.7 and also 10.6 indifferent crystals) (2).

The diameter ofthe B-DNA helix (the distance in between phosphorus atoms ofone complementary base pair) equals 2nm, and also purine and pyrimidine bases accounting 3/5 and also 2/5 ofthis distance, respectively. The depths ofthe young and major grooves room 0.85nm and 0.75nm, respectively. Atthe same time, the significant groove isapproximately 2 times broader (1.2nm) than the minor groove (3).

Ithas been presented that inthe higher salt concentrations orwith the enhancement ofnon-electrolytes (e.g., ethanol), the DNA structure may adjust from theB totheA form. The deoxyribose ring transforms its conformation from the C2-endo tothe C3-endo form. The bases incline towards the axis byapproximately 13o. Inthis form, there room 11base bag per turn (4).


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The A-DNA and B-DNA structures differ considerably inthat inthe B-form, the basic pairs room tilted with respect tothe helix axis byalmost half ofits radius. Asaresult, acavity appears along the axis ofthe molecule, the significant groove i do not care deeper and an ext narrow, conversely, the minor groove becomes wider and flatter (5). The BtoA revolution occurs no only as soon as the relative humidity ofthe sample islowered but additionally when the heteroduplex with RNA isformed. A-DNA appears more stable early out tothe additionalOH group inthe ribose; thus, inthe procedure ofreplication, A-DNA constantly exists inthe cell during transcription, reverse transcription, and RNA-primer annealing.

Inaddition totheA andB creates ofDNA, aZ type ofdouble-stranded DNA has likewise been reported. Uneven theA andB forms, Z-DNA isaleft-handed double helical framework with a4.4-nm turn length and also 12base pairs every turn. Under conditions oflow humidity and inthe existence ofcertain salts, some components ofthe DNA molecule wealthy inpurine-pyrimidine order (stretches ofalternatingG and also Csequences) are particularly prone toconversion right into theZ form. The presence ofZ-DNA ischaracteristic ofsome enhancers (6, 7). This form may monitor the action ofRNA polymerase since ofthe an unfavorable super coiling ofthe DNA molecule.

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Other creates ofthe DNA dual helix, such asH, B`, С, and Dforms, have likewise been described. However, these develops ofDNA room rare and also are not asphysiologically pertinent asthe forms described above.


Peterson CL and Laniel MA., Curr Biol. 2004 Jul 27;14(14):R546-51 Baikalov I. Et al., J Mol Biol. 1993 Jun 5;231(3):768-84. Lipanov A. Et al., J Mol Biol. 2000 Jul 28;300(5):1113-31. Auffinger P. Et al., J Mol Biol. 1995 may 5;248(3):662-78. Eisenstein M. Et al., Science. 1987 Nov 6;238(4828):773-7. Wong B. Et al., Proc Natl Acad Sci U S A. 2007 Feb 13;104(7):2229-34 Shin SI et al., DNA Res. 2016 Jul 3. Pii: dsw031.