Mean field theory for the intermolecular and intramolecular conformational transitions of a single flexible polyelectrolyte chain

Cell-Fate Determination from Embryo to Cancer Development: Genomic Mechanism Elucidated

Elucidation of the genomic mechanism that guides the cell-fate change is one of the fundamental issues of biology. We previously demonstrated that whole genome expression is coordinated by the emergence of a critical point at both the cell-population and single-cell levels through the physical principle of self-organized criticality. In this paper, we further examine the genomic mechanism that determines the cell-fate changes from embryo to cancer development. The state of the critical point, acting as the organizing center of the cell fate, determines whether the genome resides in a super- or sub-critical state. In the super-critical state, a specific stochastic perturbation can spread over the entire system through the "genome engine", an autonomous critical-control genomic system, whereas in the sub-critical state, the perturbation remains at a local level. The cell-fate changes when the genome becomes super-critical. We provide a consistent framework to develop a time-evolutional transition theory for the biological regulation of the cell-fate change.

DNA condensation at freestanding cationic lipid bilayers

We describe a previously unreported coil-globule transition of DNA electrostatically bound to a freestanding fluid cationic lipid membrane. The collapse of a DNA coil into a compact globule takes place after the DNA molecule attaches in an extended conformation to the membrane. DNA condensation is favored at a higher cationic lipid content, while at lower membrane charge densities coexistence of DNA random coils, partially collapsed conformations, and globules is observed.

Effective charge and coil-globule transition of a polyelectrolyte chain

Considering the adsorption of counterions on an isolated polyelectrolyte (PE) chain and using a variational theory, phase boundaries and the critical point for the first-order coil-globule transition are calculated. The transition is induced cooperatively by counterion adsorption and chain conformations and the calculation is done self-consistently. The size of the PE chain is a single-valued function of charge. The discontinuous transition of the coil size is accompanied by a discontinuous transition of the charge. Phase boundaries for the coil-globule transitions induced by both Coulomb strength (inverse temperature or dielectric constant) and ionic strength (salt) show that the PE chain collapses at a substantially lower Coulomb strength in the presence of salt. In the expanded state of the coil, an analytical formula is derived for the effective charge of the chain for conditions where the coupling between chain conformations and counterion adsorption is weak. In general, the dielectric heterogeneity of the solvent close to the polymer backbone is found to play a crucial role in the charge regularization and the chain collapse.