355 research outputs found
Entropy involved in fidelity of DNA replication
Information has an entropic character which can be analyzed within the
Statistical Theory in molecular systems. R. Landauer and C.H. Bennett showed
that a logical copy can be carried out in the limit of no dissipation if the
computation is performed sufficiently slowly. Structural and recent
single-molecule assays have provided dynamic details of polymerase machinery
with insight into information processing. We introduce a rigorous
characterization of Shannon Information in biomolecular systems and apply it to
DNA replication in the limit of no dissipation. Specifically, we devise an
equilibrium pathway in DNA replication to determine the entropy generated in
copying the information from a DNA template in the absence of friction. Both
the initial state, the free nucleotides randomly distributed in certain
concentrations, and the final state, a polymerized strand, are mesoscopic
equilibrium states for the nucleotide distribution. We use empirical stacking
free energies to calculate the probabilities of incorporation of the
nucleotides. The copied strand is, to first order of approximation, a state of
independent and non-indentically distributed random variables for which the
nucleotide that is incorporated by the polymerase at each step is dictated by
the template strand, and to second order of approximation, a state of
non-uniformly distributed random variables with nearest-neighbor interactions
for which the recognition of secondary structure by the polymerase in the
resultant double-stranded polymer determines the entropy of the replicated
strand. Two incorporation mechanisms arise naturally and their biological
meanings are explained. It is known that replication occurs far from
equilibrium and therefore the Shannon entropy here derived represents an upper
bound for replication to take place. Likewise, this entropy sets a universal
lower bound for the copying fidelity in replication.Comment: 25 pages, 5 figure
Revolución e iglesia en Nicaragua a través del relato de vida de Fernando Cardenal
En este artículo vamos a tratar sobre la figura de Fernando Cardenal, jesuita nicaragüense que, durante su noviciado en Medellín, conoció de cerca la pobreza de sus habitantes. Juró dedicar el resto de su vida a combatirla. Su paso por la clandestinidad, la dirección de la Cruzada de alfabetización, su cargo en el Ministerio de Educación, su expulsión de la Compañía de Jesús (y posterior reingreso), así como su salida del Frente Sandinista son la consecuencia de aquel juramento . A todo ello nos referimos en la presente publicación
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