Collective force generated by multiple biofilaments can exceed the sum of forces due to individual ones

Collective dynamics and force generation by cytoskeletal filaments are crucial in many cellular processes. Investigating growth dynamics of a bundle of N independent cytoskeletal filaments pushing against a wall, we show that chemical switching (ATP/GTP hydrolysis) leads to a collective phenomenon that is currently unknown. Obtaining force-velocity relations for different models that capture chemical switching, we show, analytically and numerically, that the collective stall force of N filaments is greater than N times the stall force of a single filament. Employing an exactly solvable toy model, we analytically prove the above result for N=2. We, further, numerically show the existence of this collective phenomenon, for N>=2, in realistic models (with random and sequential hydrolysis) that simulate actin and microtubule bundle growth. We make quantitative predictions for the excess forces, and argue that this collective effect is related to the non-equilibrium nature of chemical switching.Comment: New J. Phys., 201

Giant number fluctuations in microbial ecologies

Statistical fluctuations in population sizes of microbes may be quite large depending on the nature of their underlying stochastic dynamics. For example, the variance of the population size of a microbe undergoing a pure birth process with unlimited resources is proportional to the square of its mean. We refer to such large fluctuations, with the variance growing as square of the mean, as Giant Number Fluctuations (GNF). Luria and Delbruck showed that spontaneous mutation processes in microbial populations exhibit GNF. We explore whether GNF can arise in other microbial ecologies. We study certain simple ecological models evolving via stochastic processes: (i) bi-directional mutation, (ii) lysis-lysogeny of bacteria by bacteriophage, and (iii) horizontal gene transfer (HGT). For the case of bi-directional mutation process, we show analytically exactly that the GNF relationship holds at large times. For the ecological model of bacteria undergoing lysis or lysogeny under viral infection, we show that if the viral population can be experimentally manipulated to stay quasi-stationary, the process of lysogeny maps essentially to one-way mutation process and hence the GNF property of the lysogens follows. Finally, we show that even the process of HGT may map to the mutation process at large times, and thereby exhibits GNF.Comment: 18 pages, 5 figure

Dilution of Social Media Privacy: Security Vulnerabilities and Psychological Implications

In the contemporary society, Facebook, WhatsApp, Twitter, and Instagram are not merely words, but are synonymous to a person’s identity. Though the extensive use of social media is capable of rendering a huge amount of benefits in terms of ease of communication, lightening marketing reach and so on, the graver sides of the same requires thorough research to evaluate its role in modelling the psychological structure of the society and the possible threats it poses to the new generation who are glued to the use of social media platforms on a daily basis. This paper aims to perform a deep dive into the psychological effects of social media platforms on the young population and attempts to experimentally relate the same with dilution of social media privacy as a possible side effect. At the same time, possible alternatives and corrective measures to such a problem are also suggested

Effects of bursty synthesis in organelle biogenesis

A fundamental question of cell biology is how cells control the number of organelles. The processes of organelle biogenesis, namely de novo synthesis, fission, fusion, and decay, are inherently stochastic, producing cell-to-cell variability in organelle abundance. In addition, experiments suggest that the synthesis of some organelles can be bursty. We thus ask how bursty synthesis impacts intracellular organelle number distribution. We develop an organelle biogenesis model with bursty de novo synthesis by considering geometrically distributed burst sizes. We analytically solve the model in biologically relevant limits and provide exact expressions for the steady-state organelle number distributions and their means and variances. We also present approximate solutions for the whole model, complementing with exact stochastic simulations. We show that bursts generally increase the noise in organelle numbers, producing distinct signatures in noise profiles depending on different mechanisms of organelle biogenesis. We also find different shapes of organelle number distributions, including bimodal distributions in some parameter regimes. Notably, bursty synthesis broadens the parameter regime of observing bimodality compared to the `non-bursty' case. Together, our framework utilizes number fluctuations to elucidate the role of bursty synthesis in producing organelle number heterogeneity in cells.Comment: 32 pages, 4 figure

Bandgap Engineering of ZnO Nanostructures through Hydrothermal Growth

he optical, electronic and magnetic properties changes with the reduction of particle sizes, this is because the nano sized structures exhibits certain unique properties different from their bulk counterpart. Bandgap engineering for nano structures is one of the prominent area of research now. All though the bandgap increases with the reduction in the particle size, however there are several other ways by which the band gap can be changed. Fast crystallization method has been reported here and is compared with the conventional method. Absorption spectra are obtained using UV-vis optical spectrometer and from the absorption spectra tauc plot is drawn to find out the band gap theoretically. The band gap of nano particles and nano rods grown with the same nano particles as seeds are found to be different. The work shows a comparative study on the resultant bandgap for ZnO nano particles and ZnO nano rods grown with hydrothermal method. It is observed that the fast crystallization method results in decreases of band gap by around .8 eV compared to conventional method.Keywords:ZnO, nano particle, nano rod,bandga

Broad-tailed force distributions and velocity ordering in a heterogeneous membrane model for collective cell migration

Correlated velocity patterns and associated large length-scale transmission of traction forces have been observed in collective live cell migration as a response to a "wound". We argue that a simple physical model of a force-driven heterogeneous elastic membrane sliding over a viscous substrate can qualitatively explain a few experimentally observed facts: (i) the growth of velocity ordering which spreads from the wound boundary to the interior, (ii) the exponential tails of the traction force distributions, and (iii) the swirling pattern of velocities in the interior of the tissue.Comment: 7 pages and 5 figure

EXTRACTION, MODIFICATION, AND CHARACTERIZATION OF NATURAL POLYMERS USED IN TRANSDERMAL DRUG DELIVERY SYSTEM: AN UPDATED REVIEW

The modified/regulated drug delivery system helps to sustain the delivery of the drug for a prolonged period. The modified drug delivery system is primarily aimed at ensuring protection, the effectiveness of the drug, and patient compliance. The transdermal drug delivery system (TDDS) falls within the modified drug delivery system, in which the goal is to deliver the drug at a fixed dose and regulated rate through the skin. Polymers are the backbone of the framework for providing transdermal systems. The polymer should be stable, non-toxic, economical, and provide a sustainable release of the drug. In general, natural polymers used in the TDDS as rate-controlling agents, protective, and stabilizing agents and also used to minimize the frequency of dosing and improve the drug’s effectiveness by localizing at the site of action. Nowadays, manufacturers are likely to use natural polymers due to many issues associated with drug release and side effects with synthetic polymers. Drug release processes from natural polymers include oxidation, diffusion, and swelling. Natural polymers may be used as the basis to achieve predetermined drug distribution throughout the body. The use of natural materials for traditional and modern types of dosage forms are gums, mucilages, resins, and plant waste etc. Thus, the main objective of this review article is to give a brief knowledge about the extraction, modification, characterization, and biomedical application of conventional natural polymers used in the transdermal drug delivery system and their future prospective

Effect of transcription factor resource sharing on gene expression noise

Gene expression is intrinsically a stochastic (noisy) process with important implications for cellular functions. Deciphering the underlying mechanisms of gene expression noise remains one of the key challenges of regulatory biology. Theoretical models of transcription often incorporate the kinetics of how transcription factors (TFs) interact with a single promoter to impact gene expression noise. However, inside single cells multiple identical gene copies as well as additional binding sites can compete for a limiting pool of TFs. Here we develop a simple kinetic model of transcription, which explicitly incorporates this interplay between TF copy number and its binding sites. We show that TF sharing enhances noise in mRNA distribution across an isogenic population of cells. Moreover, when a single gene copy shares it\u27s TFs with multiple competitor sites, the mRNA variance as a function of the mean remains unaltered by their presence. Hence, all the data for variance as a function of mean expression collapse onto a single master curve independent of the strength and number of competitor sites. However, this result does not hold true when the competition stems from multiple copies of the same gene. Therefore, although previous studies showed that the mean expression follows a universal master curve, our findings suggest that different scenarios of competition bear distinct signatures at the level of variance. Intriguingly, the introduction of competitor sites can transform a unimodal mRNA distribution into a multimodal distribution. These results demonstrate the impact of limited availability of TF resource on the regulation of noise in gene expression

Dilution of Social Media Privacy: Security Vulnerabilities and Psychological Implications

In the contemporary society, Facebook, WhatsApp, Twitter, and Instagram are not merely words, but are synonymous to a person’s identity. Though the extensive use of social media is capable of rendering a huge amount of benefits in terms of ease of communication, lightening marketing reach and so on, the graver sides of the same requires thorough research to evaluate its role in modelling the psychological structure of the society and the possible threats it poses to the new generation who are glued to the use of social media platforms on a daily basis. This paper aims to perform a deep dive into the psychological effects of social media platforms on the young population and attempts to experimentally relate the same with dilution of social media privacy as a possible side effect. At the same time, possible alternatives and corrective measures to such a problem are also suggested