14,907 research outputs found
A lattice polymer study of DNA renaturation dynamics
DNA renaturation is the recombination of two complementary single strands to
form a double helix. It is experimentally known that renaturation proceeds
through the formation of a double stranded nucleus of several base pairs (the
rate limiting step) followed by a much faster zippering. We consider a lattice
polymer model undergoing Rouse dynamics and focus on the nucleation of two
diffusing strands. We study numerically the dependence of various nucleation
rates on the strand lengths and on an additional local nucleation barrier. When
the local barrier is sufficiently high, all renaturation rates considered scale
with the length as predicted by Kramers' rate theory and are also in agreement
with experiments: their scaling behavior is governed by exponents describing
equilibrium properties of polymers. When the local barrier is lowered
renaturation occurs in a regime of genuine non-equilibrium behavior and the
scaling deviates from the rate theory prediction.Comment: 13 pages, 6 figures. To appear in Journal of Statistical Mechanic
Investigation of DNA denaturation in Peyrard-Bishop-Dauxois model by molecular dynamics method
The phase transition of duplex into the denaturated
state is studied in the Peyrard-Bishop-Dauxois model by the method of direct
molecular-dynamical modeling. The temperature dependencies of the total energy
and heat capacity of the duplex are calculated. The approach applied can be
used to calculate the statistical properties of the duplexes of any length and
nucleotide composition.Comment: 6 pages, 4 figure
Free energy landscape and characteristic forces for the initiation of DNA unzipping
DNA unzipping, the separation of its double helix into single strands, is
crucial in modulating a host of genetic processes. Although the large-scale
separation of double-stranded DNA has been studied with a variety of
theoretical and experimental techniques, the minute details of the very first
steps of unzipping are still unclear. Here, we use atomistic molecular dynamics
(MD) simulations, coarse-grained simulations and a statistical-mechanical model
to study the initiation of DNA unzipping by an external force. The calculation
of the potential of mean force profiles for the initial separation of the first
few terminal base pairs in a DNA oligomer reveal that forces ranging between
130 and 230 pN are needed to disrupt the first base pair, values of an order of
magnitude larger than those needed to disrupt base pairs in partially unzipped
DNA. The force peak has an "echo," of approximately 50 pN, at the distance that
unzips the second base pair. We show that the high peak needed to initiate
unzipping derives from a free energy basin that is distinct from the basins of
subsequent base pairs because of entropic contributions and we highlight the
microscopic origin of the peak. Our results suggest a new window of exploration
for single molecule experiments.Comment: 25 pages, 6 figures , Accepted for publication in Biophysical Journa
Breathing dynamics in heteropolymer DNA
While the statistical mechanical description of DNA has a long tradition,
renewed interest in DNA melting from a physics perspective is nourished by
measurements of the fluctuation dynamics of local denaturation bubbles by
single molecule spectroscopy. The dynamical opening of DNA bubbles (DNA
breathing) is supposedly crucial for biological functioning during, for
instance, transcription initiation and DNA's interaction with selectively
single-stranded DNA binding proteins. Motivated by this, we consider the bubble
breathing dynamics in a heteropolymer DNA based on a (2+1)-variable master
equation and complementary stochastic Gillespie simulations, providing the
bubble size and the position of the bubble along the sequence as a function of
time. We utilize new experimental data that independently obtain stacking and
hydrogen bonding contributions to DNA stability. We calculate the spectrum of
relaxation times and the experimentally measurable autocorrelation function of
a fluorophore-quencher tagged base-pair, and demonstrate good agreement with
fluorescence correlation experiments. A significant dependence of opening
probability and waiting time between bubble events on the local DNA sequence is
revealed and quantified for a promoter sequence of the T7 phage. The strong
dependence on sequence, temperature and salt concentration for the breathing
dynamics of DNA found here points at a good potential for nanosensing
applications by utilizing short fluorophore-quencher dressed DNA constructs.Comment: 11 pages, 8 figure
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Continuous Flow vs. Static Chamber μPCR Devices on Flexible Polymeric Substrates
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Two types of μPCR devices, a continuous flow and a static chamber device, fabricated on flexible polymeric substrates are compared in the current computational study. Laminar flow, heat transfer in both solid and fluid, mass conservation of species, and reaction kinetics of PCR are coupled using COMSOL. The comparison is performed under same conditions; same material stack (based on flexible polymeric films with integrated microheaters), same species initial concentrations, amplification of the same volume of fluid sample, and implementation of the same PCR protocol. Performance is quantified in terms of DNA amplification, energy consumption, and total operating time. The calculations show that the efficiency of DNA amplification is higher in the continuous flow device. However, the continuous flow device requires (~6 times) greater energy consumption which is justified by the smaller thermal mass of the static chamber device. As regards the speed, the total time required for the static chamber μPCR is comparable to the time for the continuous flow μPCR
Finding the optimum activation energy in DNA breathing dynamics: A Simulated Annealing approach
We demonstrate how the stochastic global optimization scheme of Simulated
Annealing can be used to evaluate optimum parameters in the problem of DNA
breathing dynamics. The breathing dynamics is followed in accordance with the
stochastic Gillespie scheme with the denaturation zones in double stranded DNA
studied as a single molecule time series. Simulated Annealing is used to find
the optimum value of the activation energy for which the equilibrium bubble
size distribution matches with a given value. It is demonstrated that the
method overcomes even large noise in the input surrogate data.Comment: 9 pages, 4 figures, iop article package include
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