Mechanical properties of DNA molecule, such as bending and longitudinal stiffnesses, the effect of its interactions with different polypeptides, as well as its behaviour in nanodevices are considered. In the past ten years, many experiments on DNA stretching have been conducted using atomic-force microscopy and other methods. The results of these experiments show that DNA molecule stretching response cannot be described by common polymer models such as worm-like chain or freely-joined chain and the stretched state of DNA is an object for many discussions. In the recent paper, single DNA molecule stretching is simulated within the framework of the elaborated coarse-grained model. The results enable us to suggest that stretching of the DNA double helix is non-uniform, its length increases due to increasing of the part of strongly stretched sites. Therefore, stretched form of DNA is double-helical with strongly stretched and weekly stretched sites, it does not experience force- induced melting.
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