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Thursday, March 2, 2017

Biochemical 'fossil' shows how life may have emerged without phosphate

Biochemical 'fossil' shows how life may have emerged without phosphate

Date:
March 2, 2017
Source:
Cell Press
Summary:
One major mystery about life's origin is how phosphate became an essential building block of genetic and metabolic machinery in cells, given its poor accessibility on early Earth. Researchers have used systems biology approaches to tackle this long-standing conundrum, providing compelling, data-driven evidence that primitive life forms may not have relied on phosphate at all. Instead, a few simple, abundant molecules could have supported the emergence of a sulfur-based, phosphate-free metabolism.
This is a schematic depiction of how an early metabolism could have expanded from an initial set of prebiotic molecules, with thioester (S) vs. phosphate (P) as the main driving force.
Credit: Joshua Goldford and Daniel Segrè
One major mystery about life's origin is how phosphate became an essential building block of genetic and metabolic machinery in cells, given its poor accessibility on early Earth. In a study published on March 9 in the journal Cell, researchers used systems biology approaches to tackle this long-standing conundrum, providing compelling, data-driven evidence that primitive life forms may not have relied on phosphate at all. Instead, a few simple, abundant molecules could have supported the emergence of a sulfur-based, phosphate-free metabolism, which expanded to form a rich network of biochemical reactions capable of supporting the synthesis of a broad category of key biomolecules.
"The significance of this work is that future efforts to understand life's origin should take into account the concrete possibility that phosphate-based processes, which are essential today, may not have been around when the first life-like processes started emerging," says senior study author Daniel Segrè (@dsegre) of Boston University. "An early phosphate-independent metabolism capable of producing several key building blocks of living systems is in principle viable."
Phosphate is essential for all living systems and is present in a large proportion of known biomolecules. A sugar-phosphate backbone forms the structural framework of nucleic acids, including DNA and RNA. Moreover, phosphate is a critical component of adenosine triphosphate (ATP), which transports chemical energy within cells, and a compound called NADH, which has several essential roles in metabolism. But it is unclear how phosphate could have assumed these central roles on primordial Earth, given its scarcity and poor accessibility.
In light of this puzzle, some have proposed that early metabolic pathways did not rely on phosphate. In many of these scenarios, sulfur and iron found on mineral surfaces are thought to have fulfilled major catalytic and energetic functions prior to the appearance of phosphate. One notable origin-of-life scenario suggests that the role of ATP was originally assumed by sulfur-containing compounds called thioesters, which are widely involved in protein, carbohydrate, and lipid metabolism. Despite the availability of iron and sulfur on early Earth, concrete evidence supporting these scenarios has been lacking.
To test the feasibility of the "iron-sulfur world hypothesis" and the "thioester world scenario," Segrè and his team used computational systems biology approaches originally developed for large-scale analyses of complex metabolic networks. The researchers used a large database to assemble the complete set of all known biochemical reactions. After exploring this so-called "biosphere-level metabolism," the researchers identified a set of eight phosphate-free compounds thought to have been available in prebiotic environments. They then used an algorithm that simulated the emergence of primitive metabolic networks by compiling all possible reactions that could have taken place in the presence of these eight compounds, which included formate, acetate, hydrogen sulfide, ammonium, carbon dioxide, water, bicarbonate, and nitrogen gas.
This analysis revealed that a few simple prebiotic compounds could support the emergence of a rich, phosphate-independent metabolic network. This core network, consisting of 315 reactions and 260 metabolites, was capable of supporting the biosynthesis of a broad category of key biomolecules such as amino acids and carboxylic acids. Notably, the network was enriched for enzymes containing iron-sulfur clusters, bolstering the idea that modern biochemistry emerged from mineral geochemistry. Moreover, thioesters rather than phosphate could have enabled this core metabolism to overcome energetic bottlenecks and expand under physiologically realistic conditions.
"Before our study, other researchers had proposed a sulfur-based early biochemistry, with hints that phosphate may not have been necessary until later," Segrè says. "What was missing until now was data-driven evidence that these early processes, rather than scattered reactions, could have constituted a highly connected and relatively rich primitive metabolic network."
Although this non-experimental evidence does not definitively prove that life started without phosphate, it provides compelling support for the iron-sulfur world hypothesis and the thioester world scenario. At the same time, the study calls into question the "RNA world hypothesis," which proposes that self-replicating RNA molecules were the precursors to all current life on Earth. Instead, the results support the "metabolism-first hypothesis," which posits that a self-sustaining phosphate-free metabolic network predated the emergence of nucleic acids. In other words, nucleic acids could have been an outcome of early evolutionary processes rather than a prerequisite for them.
"Evidence that an early metabolism could have functioned without phosphate indicates that phosphate may have not been an essential ingredient for the onset of cellular life," says first author Joshua Goldford of Boston University. "This proto-metabolic system would have required an energy source and may have emerged either on the Earth's surface, with solar energy as the main driving force, or in the depth of the oceans near hydrothermal vents, where geochemical gradients could have driven the first life-like processes."
In future studies, the researchers will continue to apply systems biology approaches to study the origin of life. "My hope is that these findings will motivate further studies of the landscape of possible historical paths of metabolism, as well as specific experiments for testing the feasibility of a phosphate-free sulfur-based core biochemistry," Segrè says. "The idea of analyzing metabolism as an ecosystem-level or even planetary phenomenon, rather than an organism-specific one, may also have implications for our understanding of microbial communities. Furthermore, it will be interesting to revisit the question of how inheritance and evolution could have worked prior to the appearance of biopolymers."

Story Source:
Materials provided by Cell PressNote: Content may be edited for style and length.

Journal Reference:
  1. Goldford et al. Remnants of an Ancient Metabolism without PhosphateCell, 2017 DOI: 10.1016/j.cell.2017.02.001

Cite This Page:
Cell Press. "Biochemical 'fossil' shows how life may have emerged without phosphate." ScienceDaily. ScienceDaily, 2 March 2017. <www.sciencedaily.com/releases/2017/03/170302133445.htm>.

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How to Digitally Record/Video a UFO sighting:


Como registar digitalmente ou gravar um vídeo de um avistamento de um UFO:




Stabilize the camera on a tripod. If there is no tripod, then set it on top of a stable, flat surface. If that is not possible lean against a wall to stabilize your body and prevent the camera from filming in a shaky, unsteady manner.

Estabilize a camera com um tripé. Se não tiver um tripé, então coloque-a em cima de uma superfície estável. Se não for possível, então encoste-se a uma parede para estabilizar o corpo e evitar que a camera registe de maneira tremida e instável.

Provide visual reference points for comparison. This includes the horizon, treetops, lampposts, houses, and geographical landmarks (i.e., Horsetooth Reservoir, Mt. Adams, etc.) Provide this in the video whenever is appropriate and doesn’t detract from what your focus is, the UFO.

Forneça pontos visuais de referência para comparação. Isso inclui o horizonte, cimo das árvores, postes de iluminação, pontos de referência geográficos (como o Reservatório de Horsetooth, Mone Adams, etc) Forneça esses pontos no vídeo sempre que for apropriado e não se distraia do que é o seu foco, o UFO/a Nave.

Narrate your videotape. Provide details of the date, time, location, and direction (N,S,E,W) you are looking in. Provide your observations on the weather, including approximate temperature, windspeed, any visible cloud cover or noticeable weather anomalies or events. Narrate on the shape, size, color, movements, approximate altitude of the UFO, etc and what it appears to be doing. Also include any unusual physical, psychological or emotional sensations you might have. Narrate any visual reference points on camera so they correlate with what the viewer will see, and thereby will be better able to understand.

Faça a narração do vídeo. Forneça pormenores sobre a data, hora, local e direcção (Norte, Sul, Este, Oeste) que está a observar. Faça observações sobre as condições atmosféricas, incluindo a temperatura aproximada, velocidade do vento, quantidade de nuvens, anomalias ou acontecimentos meteorológicos evidentes. Descreva a forma, o tamanho, a cor, os movimentos, a altitude aproximada onde se encontra o UFO/nave, etc e o que aparenta estar a fazer. Inclua também quaisquer aspectos pouco habituais de sensações físicas, psicológicas ou emocionais que possa ter. Faça a narração de todos os pontos de referência visual que o espectador irá ver e que, deste modo, será capaz de compreender melhor.

Be persistent and consistent. Return to the scene to videotape and record at this same location. If you have been successful once, the UFO sightings may be occurring in this region regularly, perhaps for specific reasons unknown, and you may be successful again. You may also wish to return to the same location at a different time of day (daylight hours) for better orientation and reference. Film just a minute or two under “normal” circumstances for comparison. Write down what you remember immediately after. As soon as you are done recording the experience/event, immediately write down your impressions, memories, thoughts, emotions, etc. so it is on the record in writing. If there were other witnesses, have them independently record their own impressions, thoughts, etc. Include in this exercise any drawings, sketches, or diagrams. Make sure you date and sign your documentation.

Seja persistente e não contraditório. Volte ao local da cena e registe o mesmo local. Se foi bem sucedido uma vez, pode ser que nessa região ocorram avistamentos de UFOs/naves com regularidade, talvez por razões específicas desconhecidas, e talvez possa ser novamente bem sucedido. Pode também desejar voltar ao mesmo lugar a horas diferentes do dia (durante as horas de luz)para ter uma orientação e referência melhor. Filme apenas um ,inuto ou dois em circunstâncias “normais” para ter um termo de comparação. Escreva tudo o que viu imediatamente após o acontecimento. Logo após ter feito o registo da experiência/acontecimento, escreva imediatamente as impressões, memórias, pensamentos, emoções, etc para que fiquem registadas por escrito. Se houver outras testemunhas, peça-lhes para registar independentemente as suas próprias impressões, pensamentos, etc. Inclua quaisquer desenhos, esbolos, diagramas. Certifique-se que data e assina o seu documento/testemunho.

Always be prepared. Have a digital camera or better yet a video camera with you, charged and ready to go, at all times. Make sure you know how to use your camera (and your cell phone video/photo camera) quickly and properly. These events can occur suddenly, unexpectedly, and often quite randomly, so you will need to be prepared.

Esteja sempre preparado, Tenha sempre uma camera digital, melhor ainda, uma camera vídeo consigo, carregada e pronta a usar sempre que necessário. Certifique-se que sabe como lidar com a sua camera (ou com o seu celular/camera fotográfica) rápida e adequadamente. Esses acontecimentos podem acontecer súbita e inesperadamente e, por vezes, acidentalmente, por isso, necessita estar preparado.

Look up. Be prepared. Report. Share.

Olhe para cima, Esteja preparado, Relate, Partilhe.

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