v.l.n.r. A-, B- and Z-DNA
A DNA, B-DNA and Z-DNA are the double helix conformations in the DNA known to be biologically active. There are also many other conformations, but A-DNA, B-DNA and Z-DNA are the best known.
The B form, which is thought to be the most common, has been described by James D. Watson and Francis Crick. The positioning of the base pairs along the axis per revolution depends strongly on the forces that each base exerts on its adjacent chain. The B-shape spins 360 ° per 10.6 base pair without stress. However, many biological processes can cause tension. A DNA segment with excessive or insufficient spiralization is called positive or negative "superspiralized" (a superhelix). DNA in a cell is typically negatively superpiralized, as a result of which the double helix can break apart from the RNA transcription. Conditions for the formation of A and Z shapes
The other two known forms of the double helix shape, the A and Z shape, differ little in their geometric shape and dimensions. The A-form appears to occur only in dried form, as used in crystallographic trials and possibly occurring in hybrid pairings with DNA and RNA strands. The DNA-segmented methylation segments can be taken by the cell for regulation. Hereby, the strings rotate counterclockwise around the helix axis and in a stretched shape. Table with the properties of the different helix shapes
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