Siam Physics Congress 2017

Ionic effects on the DNA denaturation and DNA unzipping

25 May 2017, 16:35

15m

Ballroom 1

Oral Atomic Physics, Quantum Physics, Molecular and Chemical Physics A15: Atomics

Speaker

Dr Sitichoke Amnuanpol (Physics department, Thammasat University)

Description

The double-stranded DNA (dsDNA) that is separated and unwound changes its structure to the single-stranded DNA (ssDNA) in response either to the thermal energy or to the external forces. For the former the thermally induced dsDNA-to-ssDNA transition, called DNA denaturation, occurs in the polymer chain reactions. For the latter the force induced dsDNA-to-ssDNA transition, called DNA unzipping, separates two strands and opens a room for RNA polymerase to transcribe the sequence of base pairs. In DNA denaturation increasing the temperature higher than melting temperature, $T>T_m$, results in ssDNA. In DNA unzipping pulling the strands with the force stronger than critical force, $F>F_c$, also results in ssDNA. In the temperature-force phase diagram the critical force $F_c(T)$ is a boundary between the low temperature, small force phase of dsDNA and the high temperature, large force phase of ssDNA. The Na${}^{+}$ concentration dependence of $T_m$ and $F_c(T)$ is studied by using the correspondence between the statistical mechanics and the time imaginary quantum mechanics. In the language of quantum mechanics the ssDNA emerges naturally as a delocalized state. Both melting temperature $T_m$ and critical force $F_c(T)$ are found to rise with increasing the Na${}^{+}$ concentration in qualitative agreement with the calorimetric experiments measuring $T_m$ and the single molecule experiments measuring $F_c$. The enhancement of DNA stability in the presence of Na${}^{+}$ ions establishes a notion of the electrostatic stiffening.