Página 7 dos resultados de 60878 itens digitais encontrados em 0.043 segundos
Resultados filtrados por Publicador: National Academy of Sciences

‣ Implementation of cell-free biological networks at steady state

Niederholtmeyer, Henrike; Stepanova, Viktoria; Maerkl, Sebastian J.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
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Transcription and translation can be performed in vitro, outside of cells, allowing the assembly of artificial genetic networks. This bottom-up approach to engineering biological networks in a completely defined and minimal environment is instructive to define the rules and limitations of network construction. It is, however, still challenging to implement complex genetic networks in vitro because the reactions are usually performed in a batch format, where reaction products accumulate and synthesis rates decline over time. Here, we addressed this problem by developing a microfluidic device to perform in vitro transcription and translation reactions in continuous mode, where synthesis rates stay constant. This allowed us to build and implement a genetic oscillator that showed sustained oscillations for extended periods of times.

‣ Emerging predictable features of replicated biological invasion fronts

Giometto, Andrea; Rinaldo, Andrea; Carrara, Francesco; Altermatt, Florian
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Biological dispersal is a key driver of several fundamental processes in nature, crucially controlling the distribution of species and affecting their coexistence. Despite its relevance for important ecological processes, however, the subject suffers an acknowledged lack of experimentation, and current assessments point at inherent limitation to predictability even in the simplest ecological settings. We show, by combining replicated experimentation on the spread of the ciliate Tetrahymena sp. with a theoretical approach based on stochastic differential equations, that information on local unconstrained movement and reproduction of organisms (including demographic stochasticity) allows reliable prediction of both the propagation speed and range of variability of invasion fronts over multiple generations.

‣ Decoupling catalytic activity from biological function of the ATPase that powers lipopolysaccharide transport

Sherman, David J.; Lazarus, Michael B.; Murphy, Lea; Liu, Charles; Walker, Suzanne; Ruiz, Natividad; Kahne, Daniel
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Gram-negative bacteria contain an unusual outer membrane that prevents the entry of most currently available antibiotics. This membrane contains a complex glycolipid, LPS, on the exterior. It is not understood how such a large molecule, which can contain hundreds of sugars and six fatty acyl chains, is transported across the cell envelope from its site of synthesis in the cytoplasmic membrane to the cell surface. Using a combination of genetics, biochemistry, and structural biology, we characterized residues in the protein that powers LPS transport to gain mechanistic insight into how ATP hydrolysis is coupled to the biological function of the transporter. These tools help us understand how to design antibiotics targeting this essential pathway.

‣ Spatially robust estimates of biological nitrogen (N) fixation imply substantial human alteration of the tropical N cycle

Sullivan, Benjamin W.; Smith, W. Kolby; Townsend, Alan R.; Nasto, Megan K.; Reed, Sasha C.; Chazdon, Robin L.; Cleveland, Cory C.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Biological nitrogen fixation (BNF) is the largest natural source of new nitrogen (N) to terrestrial ecosystems. Tropical forest ecosystems are a putative global hotspot of BNF, but direct, spatially explicit measurements in the biome are virtually nonexistent. Nonetheless, robust estimates of tropical forest BNF are critical for understanding how these important ecosystems may respond to global change and assessing human perturbations to the N cycle. Here, we introduce a spatial sampling method to assess BNF and present evidence that tropical forest BNF is much lower than previously assumed. Our results imply that humans have roughly doubled N inputs to the tropical forest biome relative to N inputs through BNF.

‣ Realized niche shift during a global biological invasion

Tingley, Reid; Vallinoto, Marcelo; Sequeira, Fernando; Kearney, Michael R.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
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Species’ distributions result from dispersal and physiological constraints, interactions with other species, and ultimately, evolution. Biological invasions result from the deliberate or accidental movement of species between regions they would not reach through natural dispersal and can cause major conservation, economic, and human health issues. However, invasions also provide fascinating insights into species’ distribution limits. We investigate the invasion of the cane toad from South America to Australia by comparing the results of two modeling approaches: one considering physiological constraints and the other considering the joint influences of physiology, dispersal, and biotic interactions. Our findings demonstrate that the cane toad is limited in its native distribution by biotic interactions but, in Australia, is free to fill its climatic potential.

‣ Expansion of the fusion stalk and its implication for biological membrane fusion

Risselada, Herre Jelger; Bubnis, Gregory; Grubmüller, Helmut
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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We focus on computing lipidic fusion pathway energetics and interpret them in a biological context. We illustrate that the progression of fast synaptic fusion may not rely on the point-like forces that are being transmitted to the membrane via the transmembrane domains of SNARE molecules. Our work bridges the many present gaps between diverse but related experiments and their interpretation, thus providing a coherent and integrative picture.

‣ Ribonucleotide reductases reveal novel viral diversity and predict biological and ecological features of unknown marine viruses

Sakowski, Eric G.; Munsell, Erik V.; Hyatt, Mara; Kress, William; Williamson, Shannon J.; Nasko, Daniel J.; Polson, Shawn W.; Wommack, K. Eric
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Within aquatic ecosystems viruses facilitate horizontal gene transfer, biogeochemical cycling, and energy transfer by infecting and lysing microbial host cells. Despite their critical role in ecosystem function we understand little of the biological, ecological, and evolutionary features of most viruses in nature. We identify ribonucleotide reductase (RNR) genes as superior markers of viral diversity. RNR genes are distributed over a broad range of viruses. The most abundant RNR genes in marine environments are from novel groups only distantly related to known viruses. Frequency distributions of RNR clades within viral metagenome sequence libraries support predictions made by the “kill the winner” hypothesis, indicating that specialist podoviruses specifically adapted to infecting abundant heterotrophic bacterioplankton predominate within the virioplankton.

‣ Biological evidence supports an early and complex emergence of the Isthmus of Panama

Bacon, Christine D.; Silvestro, Daniele; Jaramillo, Carlos; Smith, Brian Tilston; Chakrabarty, Prosanta; Antonelli, Alexandre
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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The formation of the Isthmus of Panama, which linked North and South America, is key to understanding the biodiversity, oceanography, atmosphere, and climate in the region. Despite its importance across multiple disciplines, the timing of formation and emergence of the Isthmus and the biological patterns it created have been controversial. Here, we analyze molecular and fossil data, including terrestrial and marine organisms, to show that biotic migrations across the Isthmus of Panama began several million years earlier than commonly assumed. An earlier evolution of the Isthmus has broad implications for the mechanisms driving global climate (e.g., Pleistocene glaciations, thermohaline circulation) as well as the rich biodiversity of the Americas.

‣ Photosynthetic metabolism of C3 plants shows highly cooperative regulation under changing environments: A systems biological analysis

Luo, Ruoyu; Wei, Haibin; Ye, Lin; Wang, Kankan; Chen, Fan; Luo, Lijun; Liu, Lei; Li, Yuanyuan; Crabbe, M. James C.; Jin, Li; Li, Yixue; Zhong, Yang
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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We studied the robustness of photosynthetic metabolism in the chloroplasts of C3 plants under drought stress and at high CO2 concentration conditions by using a method called Minimization of Metabolic Adjustment Dynamic Flux Balance Analysis (M_DFBA). Photosynthetic metabolism in the chloroplasts of C3 plants applies highly cooperative regulation to minimize the fluctuation of metabolite concentration profiles in the face of transient perturbations. Our work suggests that highly cooperative regulation assures the robustness of the biological system and that there is closer cooperation under perturbation conditions than under normal conditions. This results in minimizing fluctuations in the profiles of metabolite concentrations, which is the key to maintaining a system's function. Our methods help in understanding such phenomena and the mechanisms of robustness for complex metabolic networks in dynamic processes.

‣ Low early-life social class leaves a biological residue manifested by decreased glucocorticoid and increased proinflammatory signaling

Miller, Gregory E.; Chen, Edith; Fok, Alexandra K.; Walker, Hope; Lim, Alvin; Nicholls, Erin F.; Cole, Steve; Kobor, Michael S.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Children reared in unfavorable socioeconomic circumstances show increased susceptibility to the chronic diseases of aging when they reach the fifth and sixth decades of life. One mechanistic hypothesis for this phenomenon suggests that social adversity in early life programs biological systems in a manner that persists across decades and thereby accentuates vulnerability to disease. Here we examine the basic tenets of this hypothesis by performing genome-wide transcriptional profiling in healthy adults who were either low or high in socioeconomic status (SES) in early life. Among subjects with low early-life SES, there was significant up-regulation of genes bearing response elements for the CREB/ATF family of transcription factors that conveys adrenergic signals to leukocytes, and significant down-regulation of genes with response elements for the glucocorticoid receptor, which regulates the secretion of cortisol and transduces its antiinflammatory actions in the immune system. Subjects from low-SES backgrounds also showed increased output of cortisol in daily life, heightened expression of transcripts bearing response elements for NF-κB, and greater stimulated production of the proinflammatory cytokine interleukin 6. These disparities were independent of subjects' current SES...

‣ Biological soil crusts accelerate the nitrogen cycle through large NO and HONO emissions in drylands

Weber, Bettina; Wu, Dianming; Tamm, Alexandra; Ruckteschler, Nina; Rodríguez-Caballero, Emilio; Steinkamp, Jörg; Meusel, Hannah; Elbert, Wolfgang; Behrendt, Thomas; Sörgel, Matthias; Cheng, Yafang; Crutzen, Paul J.; Su, Hang; Pöschl, Ulrich
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Text
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Biological soil crusts (biocrusts), occurring on ground surfaces in drylands throughout the world, are among the oldest life forms consisting of cyanobacteria, lichens, mosses, and algae plus heterotrophic organisms in varying proportions. They prevent soil erosion and nurture ecosystems by fixing carbon and nitrogen from the atmosphere. Here, we show that the fixed nitrogen is processed within the biocrusts, and during this metabolic activity, nitrogen oxide and nitrous acid are released to the atmosphere. Both of these gases are highly relevant, as they influence the radical formation and oxidizing capacity of the lower atmosphere, also interacting with climate change. In drylands, biocrusts appear to play a key role both in nitrogen fixation and the release of atmospheric reactive nitrogen.