62 research outputs found
Constraints, Histones, and the 30 Nanometer Spiral
We investigate the mechanical stability of a segment of DNA wrapped around a
histone in the nucleosome configuration. The assumption underlying this
investigation is that the proper model for this packaging arrangement is that
of an elastic rod that is free to twist and that writhes subject to mechanical
constraints. We find that the number of constraints required to stabilize the
nuclesome configuration is determined by the length of the segment, the number
of times the DNA wraps around the histone spool, and the specific constraints
utilized. While it can be shown that four constraints suffice, in principle, to
insure stability of the nucleosome, a proper choice must be made to guarantee
the effectiveness of this minimal number. The optimal choice of constraints
appears to bear a relation to the existence of a spiral ridge on the surface of
the histone octamer. The particular configuration that we investigate is
related to the 30 nanometer spiral, a higher-order organization of DNA in
chromatin.Comment: ReVTeX, 15 pages, 18 figure
Hydrolytic and enzymatic degradation of a poly(ĂĄ-caprolactone) network
“NOTICE: this is the author’s version of a work that was accepted for publication in Polymer Degradation and Stability. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Polymer Degradation and Stability, [Volume 97, Issue 8, August 2012, Pages 1241–1248] DOI 10.1016/j.polymdegradstab.2012.05.038Long-term hydrolytic and enzymatic degradation profiles of poly(å-caprolactone) (PCL) networks were obtained. The hydrolytic degradation studies were performed in water and phosphate buffer solution (PBS) for 65 weeks. In this case, the degradation rate of PCL networks was faster than previous results in the literature on linear PCL, reaching a weight loss of around 20% in 60 weeks after immersing the samples either in water or in PBS conditions. The enzymatic degradation rate in Pseudomonas Lipase for 14 weeks was also studied, with the conclusion that the degradation profile of PCL networks is lower than for linear PCL, also reaching a 20% weight loss. The weight lost, degree of swelling, and calorimetric and mechanical properties were obtained as a function of degradation time. Furthermore, the morphological changes in the samples were studied carefully through electron microscopy and crystal size through X-ray diffraction. The changes in some properties over the degradation period such as crystallinity, crystal size and Young¿s modulus were smaller in the case of enzymatic studies, highlighting differences in the degradation mechanism in the two studies, hydrolytic and enzymatic.The authors would like to acknowledge the support of the Spanish Ministry of Science and Education through the DPI2010-20399-004-03 project. JM Meseguer-Duenas and A Vidaurre also would like to acknowledge the support of the CIBER-BBN, an initiative funded by the VI National R&D&i Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program, CIBER Actions and financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund. The translation of this paper was funded by the Universidad Politecnica de Valencia, SpainCastilla Cortázar, MIC.; Más Estellés, J.; Meseguer Dueñas, JM.; Escobar Ivirico, JL.; Marà Soucase, B.; Vidaurre, A. (2012). Hydrolytic and enzymatic degradation of a poly(å-caprolactone) network. Polymer Degradation and Stability. 97(8):1241-1248. https://doi.org/10.1016/j.polymdegradstab.2012.05.038S1241124897
Increasing occurence of tumour cell ? Tumour cell emperipolesis in the regenerating JB-1 ascites tumour
Determination of left ventricular mass in systemic hypertension: comparison of standard and signal averaged electrocardiography.
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