Strange Cousins: Molecular Alternatives to DNA, RNA Offer New Insight Into Life’s Origins
ScienceDaily (Apr. 19, 2012) — Living systems owe their existence to a pair of information-carrying molecules: DNA and RNA. These fundamental chemical forms possess two features essential for life: they display heredity — meaning they can encode and pass on genetic information, and they can adapt over time, through processes of Darwinian evolution.
A long-debated question is whether heredity and evolution could be performed by molecules other than DNA and RNA.
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Early Evolution of Life: Study of Ribosome Evolution Challenges ‘RNA World’ Hypothesis
ScienceDaily (Mar. 12, 2012) — In the beginning — of the ribosome, the cell’s protein-building workbench — there were ribonucleic acids, the molecules we call RNA that today perform a host of vital functions in cells. And according to a new analysis, even before the ribosome’s many working parts were recruited for protein synthesis, proteins also were on the scene and interacting with RNA. This finding challenges a long-held hypothesis about the early evolution of life.
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7 Theories on the Origin of Life
Primordial soup
Life on Earth began more than 3 billion years ago, evolving from the most basic of microbes into a dazzling array of complexity over time. But how did the first organisms on the only known home to life in the universe develop from the primordial soup? Here are science’s theories on the origins of life on Earth.
Electric Spark
Electric sparks can generate amino acids and sugars from an atmosphere loaded with water, methane, ammonia and hydrogen, as was shown in the famous Miller-Urey experiment reported in 1953, suggesting that lightning might have helped create the key building blocks of life on Earth in its early days. Over millions of years, larger and more complex molecules could form. Although research since then has revealed the early atmosphere of Earth was actually hydrogen-poor, scientists have suggested that volcanic clouds in the early atmosphere might have held methane, ammonia and hydrogen and been filled with lightning as well.
Community Clay
The first molecules of life might have met on clay, according to an idea elaborated by organic chemist Alexander Graham Cairns-Smith at the University of Glasgow in Scotland. These surfaces might not only have concentrated these organic compounds together, but also helped organize them into patterns much like our genes do now.
The main role of DNA is to store information on how other molecules should be arranged. Genetic sequences in DNA are essentially instructions on how amino acids should be arranged in proteins. Cairns-Smith suggests that mineral crystals in clay could have arranged organic molecules into organized patterns. After a while, organic molecules took over this job and organized themselves.
Deep-Sea Vents
The deep-sea vent theory suggests that life may have begun at submarine hydrothermal vents, spewing key hydrogen-rich molecules. Their rocky nooks could then have concentrated these molecules together and provided mineral catalysts for critical reactions. Even now, these vents, rich in chemical and thermal energy, sustain vibrant ecosystems.
Chilly Start
Ice might have covered the oceans 3 billion years ago, as the sun was about a third less luminous than it is now. This layer of ice, possibly hundreds of feet thick, might have protected fragile organic compounds in the water below from ultraviolet light and destruction from cosmic impacts. The cold might have also helped these molecules to survive longer, allowing key reactions to happen.
RNA World
Nowadays DNA needs proteins in order to form, and proteins require DNA to form, so how could these have formed without each other? The answer may be RNA, which can store information like DNA, serve as an enzyme like proteins, and help create both DNA and proteins. Later DNA and proteins succeeded this “RNA world,” because they are more efficient. RNA still exists and performs several functions in organisms, including acting as an on-off switch for some genes. The question still remains how RNA got here in the first place. And while some scientists think the molecule could have spontaneously arisen on Earth, others say that was very unlikely to have happened.
Other nucleic acids other than RNA have been suggested as well, such as the more esoteric PNA or TNA.
Simple Beginnings
Instead of developing from complex molecules such as RNA, life might have begun with smaller molecules interacting with each other in cycles of reactions. These might have been contained in simple capsules akin to cell membranes, and over time more complex molecules that performed these reactions better than the smaller ones could have evolved, scenarios dubbed “metabolism-first” models, as opposed to the “gene-first” model of the “RNA world” hypothesis.
Panspermia
Perhaps life did not begin on Earth at all, but was brought here from elsewhere in space, a notion known as panspermia. For instance, rocks regularly get blasted off Mars by cosmic impacts, and a number of Martian meteorites have been found on Earth that some researchers have controversially suggested brought microbes over here, potentially making us all Martians originally. Other scientists have even suggested that life might have hitchhiked on comets from other star systems. However, even if this concept were true, the question of how life began on Earth would then only change to how life began elsewhere in space.
Image Credits: NASA/JPL, stock.xchng, Chemistry, MARUM, Eric Rignot & NASA JPL, © Yunxiang987 | Dreamstime.com, © Mark Rasmussen | Dreamstime.com
thenewenlightenmentage:
“Titan is just covered in carbon-bearing material — it’s a giant factory of organic chemicals,” according to Ralph Lorenz of Johns Hopkins University Applied Physics Laboratory. “We are carbon-based life, and understanding how far along the chain of complexity towards life that chemistry can go in an environment like Titan will be important in understanding the origins of life throughout the universe.”
Continue reading “Saturn’s Titan: Clues to the Origins of Life in the Universe?” »
Did Life’s First Cells Evolve in Geothermal Pools?
Based on some fundamental characteristics of cellular proteins, a team of scientists speculates that the last common ancestor of life on Earth got its start in the planet’s natural hot tubs.
Earth started as a violent place, its surface churned by continuous volcanic eruptions and cloaked in an atmosphere that would have been poisonous to today’s life-forms. Furthermore, the thin primeval atmosphere may have provided only scant protection from the young sun’s harsh ultraviolet glare. Given these inhospitable conditions, scientists have long wondered: How did the first cells come to be nearly four billion years ago?
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Scientist Suggests Life Began in Freshwater Pond, not the Ocean
(PhysOrg.com) — For most everyone alive today, it’s almost a fundamental fact. Life began in the ocean and evolved into all of the different organisms that exist today. The idea that this could be wrong causes great discomfort, like discovering as an adult that you were adopted as a child. Nonetheless, a team of diverse scientists led by Armen Mulkidjanian is suggesting that very thing; instead of life beginning in deep thermal vents in the ocean, the prevailing view, they say it perhaps instead started in landlocked freshwater pools created by thermal vapor. Their theory is based, as they explain in their paper published in the Proceedings of the National Academy of Sciences, mostly on the idea that the sea is just too salty to provide the ideal conditions necessary to spur life into existence.
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Debate Bubbles over the Origin of Life
How life began is one of nature’s enduring mysteries. Fossil and biological clues have led scientists to estimate that cells originated on this planet about four billion years ago, but exactly what catalysed their emergence has remained elusive.
In an 1871 letter to botanist Joseph Hooker, Charles Darwin wondered whether life might have begun “in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, etc. present.” Since then, scientists have come to conclude that life began in hydrothermal vents in the deep sea, but a controversial study published this week in Proceedings of the National Academy of Sciences1 argues that Darwin might have been on the right track.
The study, led by Armen Mulkidjanian of Germany’s University of Osnabrück, suggests that inland pools of condensed and cooled geothermal vapour have the ideal characteristics for the origin of life. The conclusion is based mainly on the chemistry of modern cells. Citing an observation made in 1926 by biochemist Archibald Macallum that the composition of the cytoplasm of modern cells differs greatly from that of seawater2, and assuming that cells have changed little over the past four billion years led the researchers to propose that modern cell chemistry would provide clues about the type of environment in which life emerged.
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non-atheist:
In short, yes. And a whole lot of them. Not the least of which is it doesn’t make any sense!
As noted in this article, Baylor Surgeon ‘Dissects’ Darwinism,
Dallas’ Baylor University Medical Center surgeon Joseph Kuhn recently described three serious problems with Darwinian evolution in a…
Apologetic garbage. This is the deception I speak of:
“Evolution has a weakness. It can’t explain the origins of life. By the way, I’m an Apologist at the Institute for Creation Research and therefore, I’m skewed to the metaphysical claims of Christianity. God is the origin of life.”
It’s vomit and nothing more. Abiogenesis is the study of the origins of life. Evolution has never attempted to explain life’s origins. If you want to know the difference between Abiogenesis and Evolution, read here and here.
Scientists Prove Plausibility of New Pathway to Life’s Chemical Building Blocks
ScienceDaily (Jan. 31, 2012) — For decades, chemists considered a chemical pathway known as the formose reaction the only route for producing sugars essential for life to begin, but more recent research has called into question the plausibility of such thinking. Now a group from The Scripps Research Institute has proven an alternative pathway to those sugars called the glyoxylate scenario, which may push the field of pre-life chemistry past the formose reaction hurdle.
The team is reporting the results of their highly successful experiments online ahead of print in the Journal of the American Chemical Society.
“We were working in uncharted territory,” says Ramanarayanan (“Ram”) Krishnamurthy, a Scripps Research chemist who led the research, “We didn’t know what to expect but the glyoxylate scenario with respect to formation of carbohydrates is not a hypothesis anymore, it’s an experimental fact.”
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Avalanche of Reactions at the Origin of Life
Mechanism of evolution of the primordial metabolism discovered
Volcanic-hydrothermal flow channels offer a chemically unique environment, which at first glance appears hostile to life. This environment is defined by cracks in the crust of the earth through which water flows. This water, laden with volcanic gases, contacts a diversity of minerals. It is precisely this extreme environment where the two mechanisms could have emerged that are at the root of all life: The multiplication of biomolecules (reproduction) and the emergence of new biomolecules on the basis of previously-formed biomolecules (evolution).
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