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Thermal Denaturation of Fluctuating DNA Driven by Bending Entropy  [PDF]
J. Palmeri,M. Manghi,N. Destainville
Physics , 2006, DOI: 10.1103/PhysRevLett.99.088103
Abstract: A statistical model of homopolymer DNA, coupling internal base pair states (unbroken or broken) and external thermal chain fluctuations, is exactly solved using transfer kernel techniques. The dependence on temperature and DNA length of the fraction of denaturation bubbles and their correlation length is deduced. The thermal denaturation transition emerges naturally when the chain fluctuations are integrated out and is driven by the difference in bending (entropy dominated) free energy between broken and unbroken segments. Conformational properties of DNA, such as persistence length and mean-square-radius, are also explicitly calculated, leading, e.g., to a coherent explanation for the experimentally observed thermal viscosity transition.
Denaturation Patterns in Heterogeneous DNA  [PDF]
Marco Zoli
Quantitative Biology , 2010, DOI: 10.1103/PhysRevE.81.051910
Abstract: The thermodynamical properties of heterogeneous DNA sequences are computed by path integral techniques applied to a nonlinear model Hamiltonian. The base pairs relative displacements are interpreted as time dependent paths whose amplitudes are consistent with the model potential for the hydrogen bonds between complementary strands. The portion of configuration space contributing to the partition function is determined, at any temperature, by selecting the ensemble of paths which fulfill the second law of thermodynamics. For a short DNA fragment, the denaturation is signaled by a succession of peaks in the specific heat plots while the entropy grows continuously versus $T$. Thus, the opening of the double strand with bubble formation appears as a smooth crossover due to base pair fluctuation effects which are accounted for by the path integral method. The multistep transition is driven by the AT-rich regions of the DNA fragment. The base pairs path ensemble shows an enhanced degree of cooperativity at about the same temperatures for which the specific heat peaks occur. These findings establish a link between microscopic and macroscopic signatures of the transition. The fractions of mean base pair stretchings are computed by varying the AT base pairs content and taking some threshold values for the occurrence of the molecule denaturation.
Statistical Mechanics of Torque Induced Denaturation of DNA  [PDF]
Simona Cocco,Remi Monasson
Physics , 1999, DOI: 10.1103/PhysRevLett.83.5178
Abstract: A unifying theory of the denaturation transition of DNA, driven by temperature T or induced by an external mechanical torque Gamma is presented. Our model couples the hydrogen-bond opening and the untwisting of the helicoidal molecular structure. We show that denaturation corresponds to a first-order phase transition from B-DNA to d-DNA phases and that the coexistence region is naturally parametrized by the degree of supercoiling sigma. The denaturation free energy, the temperature dependence of the twist angle, the phase diagram in the T,Gamma plane and isotherms in the sigma, Gamma plane are calculated and show a good agreement with experimental data.
Bubbles and denaturation in DNA  [PDF]
Titus S. van Erp,Santiago Cuesta-Lopez,Michel Peyrard
Physics , 2006, DOI: 10.1140/epje/i2006-10032-2
Abstract: The local opening of DNA is an intriguing phenomenon from a statistical physics point of view, but is also essential for its biological function. For instance, the transcription and replication of our genetic code can not take place without the unwinding of the DNA double helix. Although these biological processes are driven by proteins, there might well be a relation between these biological openings and the spontaneous bubble formation due to thermal fluctuations. Mesoscopic models, like the Peyrard-Bishop-Dauxois model, have fairly accurately reproduced some experimental denaturation curves and the sharp phase transition in the thermodynamic limit. It is, hence, tempting to see whether these models could be used to predict the biological activity of DNA. In a previous study, we introduced a method that allows to obtain very accurate results on this subject, which showed that some previous claims in this direction, based on molecular dynamics studies, were premature. This could either imply that the present PBD should be improved or that biological activity can only be predicted in a more complex frame work that involves interactions with proteins and super helical stresses. In this article, we give detailed description of the statistical method introduced before. Moreover, for several DNA sequences, we give a thorough analysis of the bubble-statistics as function of position and bubble size and the so-called $l$-denaturation curves that can be measured experimentally. These show that some important experimental observations are missing in the present model. We discuss how the present model could be improved.
Observations of an Impurity-driven Hysteresis Behavior in Ice Crystal Growth at Low Pressure  [PDF]
Kenneth G. Libbrecht
Physics , 2008,
Abstract: We describe observations of a novel hysteresis behavior in the growth of ice crystals under near-vacuum conditions. Above a threshold supersaturation, we find that the ice growth rate often exhibits a sudden increase that we attribute to an impurity-driven growth instability. We examine possible mechanisms for this instability, which can be used to produce clean, faceted ice surfaces.
The dynamics of the DNA denaturation transition  [PDF]
Titus S. van Erp,Michel Peyrard
Physics , 2012, DOI: 10.1209/0295-5075/98/48004
Abstract: The dynamics of the DNA denaturation is studied using the Peyrard-Bishop-Dauxois model. The denaturation rate of double stranded polymers decreases exponentially as function of length below the denaturation temperature. Above Tc, the rate shows a minimum, but then increases as function of length. We also examine the influence of sequence and solvent friction. Molecules having the same number of weak and strong base-pairs can have significantly different opening rates depending on the order of base-pairs.
There and (slowly) back again: Entropy-driven hysteresis in a model of DNA overstretching  [PDF]
Stephen Whitelam,Sander Pronk,Phillip L. Geissler
Quantitative Biology , 2006, DOI: 10.1529/biophysj.107.117036
Abstract: When pulled along its axis, double-stranded DNA elongates abruptly at a force of about 65 pN. Two physical pictures have been developed to describe this overstretched state. The first proposes that strong forces induce a phase transition to a molten state consisting of unhybridized single strands. The second picture instead introduces an elongated hybridized phase, called S-DNA, structurally and thermodynamically distinct from standard B-DNA. Little thermodynamic evidence exists to discriminate directly between these competing pictures. Here we show that within a microscopic model of DNA we can distinguish between the dynamics associated with each. In experiment, considerable hysteresis in a cycle of stretching and shortening develops as temperature is increased. Since there are few possible causes of hysteresis in a system whose extent is appreciable in only one dimension, such behavior offers a discriminating test of the two pictures of overstretching. Most experiments are performed upon nicked DNA, permitting the detachment (`unpeeling') of strands. We show that the long-wavelength progression of the unpeeled front generates hysteresis, the character of which agrees with experiment only if we assume the existence of S-DNA. We also show that internal melting (distinct from unpeeling) can generate hysteresis, the degree of which is strongly dependent upon the nonextensive loop entropy of single-stranded DNA.
Supercoil formation in DNA denaturation  [PDF]
A. Kabakcioglu,E. Orlandini,D. Mukamel
Quantitative Biology , 2008,
Abstract: We generalize the Poland-Scheraga (PS) model to the case of a circular DNA, taking into account the twisting of the two strains around each other. Guided by recent single-molecule experiments on DNA strands, we assume that the torsional stress induced by denaturation enforces formation of supercoils whose writhe absorbs the linking number expelled by the loops. Our model predicts that, when the entropy parameter of a loop satisfies $c \le 2$, denaturation transition does not take place. On the other hand for $c>2$ a first-order denaturation transition is consistent with our model and may take place in the actual system, as in the case with no supercoils. These results are in contrast with other treatments of circular DNA melting where denaturation is assumed to be accompanied by an increase in twist rather than writhe on the bound segments.
Denaturation transition of stretched DNA  [PDF]
Andreas Hanke,Martha G. Ochoa,Ralf Metzler
Quantitative Biology , 2007, DOI: 10.1103/PhysRevLett.100.018106
Abstract: We generalize the Poland-Scheraga model to consider DNA denaturation in the presence of an external stretching force. We demonstrate the existence of a force-induced DNA denaturation transition and obtain the temperature-force phase diagram. The transition is determined by the loop exponent $c$ for which we find the new value $c=4\nu-1/2$ such that the transition is second order with $c=1.85<2$ in $d=3$. We show that a finite stretching force $F$ destabilizes DNA, corresponding to a lower melting temperature $T(F)$, in agreement with single-molecule DNA stretching experiments.
Denaturation of Heterogeneous DNA  [PDF]
D. Cule,T. Hwa
Physics , 1997, DOI: 10.1103/PhysRevLett.79.2375
Abstract: The effect of heterogeneous sequence composition on the denaturation of double stranded DNA is investigated. The resulting pair-binding energy variation is found to have a negligible effect on the critical properties of the smooth second order melting transition in the simplest (Peyrard-Bishop) model. However, sequence heterogeneity is dramatically amplified upon adopting a more realistic treatment of the backbone stiffness. The model yields features of ``multi-step melting'' similar to those observed in experiments.
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