The Role of Methylation in the Intrinsic Dynamics of B- and Z-DNA

Methylation of cytosine at the 5-carbon position (5mC) is observed in both prokaryotes and eukaryotes. In humans, DNA methylation at CpG sites plays an important role in gene regulation and has been implicated in development, gene silencing, and cancer. In addition, the CpG dinucleotide is a known hot spot for pathologic mutations genome-wide. CpG tracts may adopt left-handed Z-DNA conformations, which have also been implicated in gene regulation and genomic instability. Methylation facilitates this B-Z transition but the underlying mechanism remains unclear. Herein, four structural models of the dinucleotide d(GC)5 repeat sequence in B-, methylated B-, Z-, and methylated Z-DNA forms were constructed and an aggregate 100 nanoseconds of molecular dynamics simulations in explicit solvent under physiological conditions was performed for each model. Both unmethylated and methylated B-DNA were found to be more flexible than Z-DNA. However, methylation significantly destabilized the BII, relative to the BI, state through the Gp5mC steps. In addition, methylation decreased the free energy difference between B- and Z-DNA. Comparisons of α/γ backbone torsional angles showed that torsional states changed marginally upon methylation for B-DNA, and Z-DNA. Methylation-induced conformational changes and lower energy differences may contribute to the transition to Z-DNA by methylated, over unmethylated, B-DNA and may be a contributing factor to biological function

A Review on the Mechanical Modeling of Composite Manufacturing Processes

© 2016, The Author(s). The increased usage of fiber reinforced polymer composites in load bearing applications requires a detailed understanding of the process induced residual stresses and their effect on the shape distortions. This is utmost necessary in order to have more reliable composite manufacturing since the residual stresses alter the internal stress level of the composite part during the service life and the residual shape distortions may lead to not meeting the desired geometrical tolerances. The occurrence of residual stresses during the manufacturing process inherently contains diverse interactions between the involved physical phenomena mainly related to material flow, heat transfer and polymerization or crystallization. Development of numerical process models is required for virtual design and optimization of the composite manufacturing process which avoids the expensive trial-and-error based approaches. The process models as well as applications focusing on the prediction of residual stresses and shape distortions taking place in composite manufacturing are discussed in this study. The applications on both thermoset and thermoplastic based composites are reviewed in detail

The Role Of Reactive Oxygen Species And Oxidative Stress In Carbon Monoxide Toxicity: An In-Depth Analysis

The underlying mechanism of the central nervous system (CNS) injury after acute carbon monoxide (CO) poisoning is interlaced with multiple factors including apoptosis, abnormal inflammatory responses, hypoxia, and ischemia/reperfusion-like problems. One of the current hypotheses with regard to the molecular mechanism of CO poisoning is the oxidative injury induced by reactive oxygen species, free radicals, and neuronal nitric oxide. Up to now, the relevant mechanism of this injury remains poorly understood. The weakening of antioxidant systems and the increase of lipid peroxidation in the CNS have been implicated, however. Accordingly, in this review, we will highlight the relationship between oxidative stress and CO poisoning from the perspective of forensic toxicology and molecular toxicology

An In Vitro and In Vivo Evaluation of Tensile Strength and Durability of Seven Suture Materials in Various pH and Different Conditions: An Experimental Study in Rats

Development in material engineering provide many kinds of suture materials to medical fields. The choice of utilization depends on the surgeons decision, the durability, absorbtion times, tensile strength of the suture, and operation site in means of organ and tissue. In this study we aimed to investigate 7 different suture materials in vivo and in vitro conditions to evaluate the properties and durability. Basal tensile strength (TS) values of all sutures were measured and 168 Wistar albino rats were utilised in vivo groups. The sutures were placed in the bladder, stomach, intestine and bile duct (after obstructive jaundice). Urine and bile of rat, pH 1 and pH 10 were used as in vitro conditions. Seven different suture materials (Maxon, Vicryl, Plain Catgut, Surgical Silk, Polypropylene, Caprosyn and Biosyn) were investigated in 9 different in vitro and in vivo conditions. All sutures were chosen to be in size 5/0. In the following 5th day the sutures were tested related to durability and stability. Results were compared stastically using the Mann-Whitney U test and p < 0.05 was considered as stastically significant. Among all the suture materials only polypropylene proved to preserve its stability in vivo and in vitro surveys. Cat-gut and caprosyn lost its TS in all medias. Silk and biosyn lost its TS in all conditions except the stomach and intestines. Maxon also lost its TS in all condition except urine. Utilisation of caprosyn and biosyn in urinary procedures reduces stone formation and infections. The suture of choice in biliary tract should be vicryl, maxon or biosyn since polypropylene preserves its stability that could result in stone formation. In intestinal operations polypropylene, vicryl, and silk could be preferred