RESUMO
This paper presents an exploratory analysis of the mitochondrial DNA (mtDNA) of 32 species in the subphylum Vertebrata, divided in 7 taxonomic classes. Multiple stochastic parameters, such as the Hurst and detrended fluctuation analysis (DFA) exponents, Shannon entropy, and Chargaff ratio are computed for each DNA sequence. The biological interpretation of these parameters leads to defining a triplet of novel indices. These new functions incorporate the long-range correlations, the probability of occurrence of nucleic bases, and the ratio of pyrimidines-to-purines. Results suggest that relevant regions in mtDNA can be located using the proposed indices. Furthermore, early results from clustering algorithms indicate that the indices introduced might be useful in phylogenetic studies.
RESUMO
We have studied theoretically the compressibility modulus B of DNA and complexation adsorption isotherms of DNA and lipids, as a function of DNA spacing d(DNA) and NaCl electrolyte concentration, respectively, in isoelectric states of lamellar DNA/cationic lipid (CL) self-assemblies. The electrostatic free energy derived from the Poisson-Boltzmann theory predicts partial agreement with measured B values for interhelical separations d(DNA)>33 A when use is made of a fit of hydration repulsion from bulk DNA hexagonal phases in solution. For lower interchain separations the prediction worsens due to the hydration interaction that overcomes the electrostatic contribution. An exact match of the system's counterion electrochemical potentials and the coions of salt in aqueous phase leads to the electrostatic part of the free energy that renders isotherms of d(DNA) versus ionic strength in qualitative consistency with general trends of available experimental data of CL-DNA complexes.
Assuntos
Biofísica/métodos , DNA/química , Eletroquímica/métodos , Lipídeos/química , Adsorção , Entropia , Íons , Focalização Isoelétrica , Substâncias Macromoleculares , Modelos Estatísticos , Conformação Molecular , Conformação de Ácido Nucleico , Eletricidade Estática , Termodinâmica , Água/químicaRESUMO
The total force between two like charged surfaces is investigated as a function of counterion concentration in aqueous solution and surfaces distance of separation. A smooth and a discrete density of surface charge sigma(s) lead to differences in the force distance curve at high sigma(s), which are negligible for low surface charge. The total force per unit area with divalent counterions is an oscillating function of sigma(s). At fixed surfaces separation and region of attraction (increasing sigma(s)), there is a variation in its strength that results from a competition between the ideal kinetic and ion-ion correlation force components as predicted from the anisotropic hypernetted chain approximation.