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New discoveries and research in abiogenesis
- Thread starter shunyadragon
- Start date
A bit technical, but an excellent article on the resolution of the problem of homochirality in the chemical abiogenesis of life.
Origin of Homochirality in Biosystems
Origin of Homochirality in Biosystems
Søren Toxvaerd
Abstract
Experimental data for a series of central and simple molecules in biosystems show that some amino acids and a simple sugar molecule have a chiral discrimination in favor of homochirality. Models for segregation of racemic mixtures of chiral amphiphiles and lipophiles in aqueous solutions show that the amphiphiles with an active isomerization kinetics can perform a spontaneous break of symmetry during the segregation and self-assembly to homochiral matter. Based on this observation it is argued that biomolecules with a sufficiently strong chiral discrimination could be the origin of homochirality in biological systems.
Keywords: Origin of chirality, Origin of Life, Prebiotic self-assambly
Go to:
1. Introduction
The homochirality of amino acids and sugar molecules in biosystems is a necessity for life, and the preservation of homochirality over long periods of time in a prebiotic fluid environment is the problem. It is the problem because it is not sufficient to obtain homochirality. Due to the active isomerization kinetics in fluid systems [1, 2], which in general drives a chiral system toward a racemic composition, it is of utmost importance to determine the condition and mechanism for preservation of homochirality in prebiotic systems. From a thermodynamical and physico-chemical point of view biosystems consist of big molecules of homochiral units and in a soft condensed state in an aqueous solution. If the origin of life is not based on an extremely rare event we therefore need an explanation of how to maintain homochirality in such a prebiotic state for millions of years. If the creation of ”simple” biosystems is obtained by a steady state synthesis, the prebiotic fluid state must necessarily have been rather constant over very long times in order to build up the very unique and complicated templates for life, where RNA is probable the original template. Even in a deterministically driven self-organisation such template-molecule is not established “overnight”. This is why a mechanism ensuring the preservation of homochirality for a very long time is needed. A period of time which is much longer than the time in which an (diluted) aqueous solution of an amino acid will racemize [1], i.e. in the order of thousands of years. Sugar molecules are much less stable than amino acids and racemize within hours or days depending on the physico-chemical conditions [2]; however, both key-molecules are central in all biosystems. Almost all theories dealing with homochirality have concentrated on explaining its origin, but, irrespective of whether L-amino acids float to us from Space or are obtained by a kind of autocatalysis, it is irrelevant, as we need to ensure its stability during long periods of time within the fluid state when biosystems were synthesized probably around 4 billion years ago. Finally it shall be emphasized that it is not sufficient to explain the origin and preservation of one of the homociral species in biosystems, e.g. D-sugars. One needs to explain the preservation of D-sugars as well as L-amino acids in a prebiotic fluid state.
The strong chiral discrimination of some of the central biomolecules offers such an explanation not only for a spontaneously break of symmetry and the origin of chirality [4], but also for the preservation of the homochiral states of D-sugar and L-amino acids.
Origin of Homochirality in Biosystems
Origin of Homochirality in Biosystems
Søren Toxvaerd
Abstract
Experimental data for a series of central and simple molecules in biosystems show that some amino acids and a simple sugar molecule have a chiral discrimination in favor of homochirality. Models for segregation of racemic mixtures of chiral amphiphiles and lipophiles in aqueous solutions show that the amphiphiles with an active isomerization kinetics can perform a spontaneous break of symmetry during the segregation and self-assembly to homochiral matter. Based on this observation it is argued that biomolecules with a sufficiently strong chiral discrimination could be the origin of homochirality in biological systems.
Keywords: Origin of chirality, Origin of Life, Prebiotic self-assambly
Go to:
1. Introduction
The homochirality of amino acids and sugar molecules in biosystems is a necessity for life, and the preservation of homochirality over long periods of time in a prebiotic fluid environment is the problem. It is the problem because it is not sufficient to obtain homochirality. Due to the active isomerization kinetics in fluid systems [1, 2], which in general drives a chiral system toward a racemic composition, it is of utmost importance to determine the condition and mechanism for preservation of homochirality in prebiotic systems. From a thermodynamical and physico-chemical point of view biosystems consist of big molecules of homochiral units and in a soft condensed state in an aqueous solution. If the origin of life is not based on an extremely rare event we therefore need an explanation of how to maintain homochirality in such a prebiotic state for millions of years. If the creation of ”simple” biosystems is obtained by a steady state synthesis, the prebiotic fluid state must necessarily have been rather constant over very long times in order to build up the very unique and complicated templates for life, where RNA is probable the original template. Even in a deterministically driven self-organisation such template-molecule is not established “overnight”. This is why a mechanism ensuring the preservation of homochirality for a very long time is needed. A period of time which is much longer than the time in which an (diluted) aqueous solution of an amino acid will racemize [1], i.e. in the order of thousands of years. Sugar molecules are much less stable than amino acids and racemize within hours or days depending on the physico-chemical conditions [2]; however, both key-molecules are central in all biosystems. Almost all theories dealing with homochirality have concentrated on explaining its origin, but, irrespective of whether L-amino acids float to us from Space or are obtained by a kind of autocatalysis, it is irrelevant, as we need to ensure its stability during long periods of time within the fluid state when biosystems were synthesized probably around 4 billion years ago. Finally it shall be emphasized that it is not sufficient to explain the origin and preservation of one of the homociral species in biosystems, e.g. D-sugars. One needs to explain the preservation of D-sugars as well as L-amino acids in a prebiotic fluid state.
The strong chiral discrimination of some of the central biomolecules offers such an explanation not only for a spontaneously break of symmetry and the origin of chirality [4], but also for the preservation of the homochiral states of D-sugar and L-amino acids.
https://phys.org/news/2020-08-life-chemical-evolution-tiny-gulf.html
Origins of life: Chemical evolution in a tiny Gulf Stream
by Ludwig Maximilian University of Munich
Hot fluids meet a cold sea: Local temperature gradients in porous volcanic rock on the early Earth could have facilitated the self-replication of RNA strands. Credit: Picture Alliance
Chemical reactions driven by the geological conditions on the early Earth might have led to the prebiotic evolution of self-replicating molecules. Scientists at Ludwig-Maximilians Universitaet (LMU) in Munich now report on a hydrothermal mechanism that could have promoted the process.
Life is a product of evolution by natural selection. That's the take-home lesson from Charles Darwin's book "The Origin of Species," published over 150 years ago. But how did the history of life on our planet begin? What kind of process could have led to the formation of the earliest forms of the biomolecules we now know, which subsequently gave rise to the first cell? Scientists believe that, on the (relatively) young Earth, environments must have existed, which were conducive to prebiotic, molecular evolution. A dedicated group of researchers is engaged in attempts to define the conditions under which the first tentative steps in the evolution of complex polymeric molecules from simple chemical precursors could have been feasible. "To get the whole process started, prebiotic chemistry must be embedded in a setting in which an appropriate combination of physical parameters causes a non-equilibrium state to prevail," explains LMU biophysicist Dieter Braun. Together with colleagues based at the Salk Institute in San Diego, he and his team have now taken a big step toward the definition of such a state. Their latest experiments have shown the circulation of warm water (provided by a microscopic version of the Gulf Stream) through pores in volcanic rock can stimulate the replication of RNA strands. The new findings appear in the journal Physical Review Letters.
As the carriers of hereditary information in all known lifeforms, RNA and DNA are at the heart of research into the origins of life. Both are linear molecules made up of four types of subunits called bases, and both can be replicated—and therefore transmitted. The sequence of bases encodes the genetic information. However, the chemical properties of RNA strands differ subtly from those of DNA. While DNA strands pair to form the famous double helix, RNA molecules can fold into three-dimensional structures that are much more varied and functionally versatile. Indeed, specifically folded RNA molecules have been shown to catalyze chemical reactions both in the test-tube and in cells, just as proteins do. These RNAs therefore act like enzymes, and are referred to as 'ribozymes." The ability to replicate and accelerate chemical transformations motivated the formulation of the "RNA world' hypothesis. This idea postulates that, during early molecular evolution, RNA molecules served both as stores of information like DNA, and as chemical catalysts. The latter role is performed by proteins in today's organisms, where RNAs are synthesized by enzymes called RNA polymerases.
Ribozymes that can link short RNA strands together—and some that can replicate short RNA templates—have been created by mutation and Darwinian selection in the laboratory. One of these "RNA polymerase' ribozymes was used in the new study.
Acquisition of the capacity for self-replication of RNA is viewed as the crucial process in prebiotic molecular evolution. In order to simulate conditions under which the process could have become established, Braun and his colleagues set up an experiment in which a 5-mm cylindrical chamber serves as the equivalent of a pore in a volcanic rock. On the early Earth, porous rocks would have been exposed to natural temperature gradients. Hot fluids percolating through rocks below the seafloor would have encountered cooler waters at the sea-bottom, for instance. This explains why submarine hydrothermal vents are the environmental setting for the origin of life most favored by many researchers. In tiny pores, temperature fluctuations can be very considerable, and give rise to heat transfer and convection currents. These conditions can be readily reproduced in the laboratory. In the new study, the LMU team verified that such gradients can greatly stimulate the replication of RNA sequences.
One major problem with ribozyme-driven scenario for replication of RNA is that the initial result of the process is a double-stranded RNA. To achieve cyclic replication, the strands must be separated ('melted'), and this requires higher temperatures, which are likely to unfold—and inactivate—the ribozyme. Braun and colleagues have now demonstrated how this can be avoided. "In our experiment, local heating of the reaction chamber creates a steep temperature gradient, which sets up a combination of convection, thermophoresis and Brownian motion," says Braun. Convection stirs the system, while thermophoresis transports molecules along the gradient in a size-dependent manner. The result is a microscopic version of an ocean current like the Gulf Stream. This is essential, as it transports short RNA molecules into warmer regions, while the larger, heat-sensitive ribozyme accumulates in the cooler regions, and is protected from melting. Indeed, the researchers were astonished to discover that the ribozyme molecules aggregated to form larger complexes, which further enhances their concentration in the colder region. In this way, the lifetimes of the labile ribozymes could be significantly extended, in spite of the relatively high temperatures. "That was a complete surprise," says Braun.
The lengths of the replicated strands obtained are still comparatively limited. The shortest RNA sequences are more efficiently duplicated than the longer, such that the dominant products of replication are reduced to a minimal length. Hence, true Darwinian evolution, which favors synthesis of progressively longer RNA strands, does not occur under these conditions. "However, based on our theoretical calculations, we are confident that further optimization of our temperature traps is feasible," says Braun. A system in which the ribozyme is assembled from shorter RNA strands, which it can replicate separately, is also a possible way forward.
Origins of life: Chemical evolution in a tiny Gulf Stream
by Ludwig Maximilian University of Munich
Hot fluids meet a cold sea: Local temperature gradients in porous volcanic rock on the early Earth could have facilitated the self-replication of RNA strands. Credit: Picture Alliance
Chemical reactions driven by the geological conditions on the early Earth might have led to the prebiotic evolution of self-replicating molecules. Scientists at Ludwig-Maximilians Universitaet (LMU) in Munich now report on a hydrothermal mechanism that could have promoted the process.
Life is a product of evolution by natural selection. That's the take-home lesson from Charles Darwin's book "The Origin of Species," published over 150 years ago. But how did the history of life on our planet begin? What kind of process could have led to the formation of the earliest forms of the biomolecules we now know, which subsequently gave rise to the first cell? Scientists believe that, on the (relatively) young Earth, environments must have existed, which were conducive to prebiotic, molecular evolution. A dedicated group of researchers is engaged in attempts to define the conditions under which the first tentative steps in the evolution of complex polymeric molecules from simple chemical precursors could have been feasible. "To get the whole process started, prebiotic chemistry must be embedded in a setting in which an appropriate combination of physical parameters causes a non-equilibrium state to prevail," explains LMU biophysicist Dieter Braun. Together with colleagues based at the Salk Institute in San Diego, he and his team have now taken a big step toward the definition of such a state. Their latest experiments have shown the circulation of warm water (provided by a microscopic version of the Gulf Stream) through pores in volcanic rock can stimulate the replication of RNA strands. The new findings appear in the journal Physical Review Letters.
As the carriers of hereditary information in all known lifeforms, RNA and DNA are at the heart of research into the origins of life. Both are linear molecules made up of four types of subunits called bases, and both can be replicated—and therefore transmitted. The sequence of bases encodes the genetic information. However, the chemical properties of RNA strands differ subtly from those of DNA. While DNA strands pair to form the famous double helix, RNA molecules can fold into three-dimensional structures that are much more varied and functionally versatile. Indeed, specifically folded RNA molecules have been shown to catalyze chemical reactions both in the test-tube and in cells, just as proteins do. These RNAs therefore act like enzymes, and are referred to as 'ribozymes." The ability to replicate and accelerate chemical transformations motivated the formulation of the "RNA world' hypothesis. This idea postulates that, during early molecular evolution, RNA molecules served both as stores of information like DNA, and as chemical catalysts. The latter role is performed by proteins in today's organisms, where RNAs are synthesized by enzymes called RNA polymerases.
Ribozymes that can link short RNA strands together—and some that can replicate short RNA templates—have been created by mutation and Darwinian selection in the laboratory. One of these "RNA polymerase' ribozymes was used in the new study.
Acquisition of the capacity for self-replication of RNA is viewed as the crucial process in prebiotic molecular evolution. In order to simulate conditions under which the process could have become established, Braun and his colleagues set up an experiment in which a 5-mm cylindrical chamber serves as the equivalent of a pore in a volcanic rock. On the early Earth, porous rocks would have been exposed to natural temperature gradients. Hot fluids percolating through rocks below the seafloor would have encountered cooler waters at the sea-bottom, for instance. This explains why submarine hydrothermal vents are the environmental setting for the origin of life most favored by many researchers. In tiny pores, temperature fluctuations can be very considerable, and give rise to heat transfer and convection currents. These conditions can be readily reproduced in the laboratory. In the new study, the LMU team verified that such gradients can greatly stimulate the replication of RNA sequences.
One major problem with ribozyme-driven scenario for replication of RNA is that the initial result of the process is a double-stranded RNA. To achieve cyclic replication, the strands must be separated ('melted'), and this requires higher temperatures, which are likely to unfold—and inactivate—the ribozyme. Braun and colleagues have now demonstrated how this can be avoided. "In our experiment, local heating of the reaction chamber creates a steep temperature gradient, which sets up a combination of convection, thermophoresis and Brownian motion," says Braun. Convection stirs the system, while thermophoresis transports molecules along the gradient in a size-dependent manner. The result is a microscopic version of an ocean current like the Gulf Stream. This is essential, as it transports short RNA molecules into warmer regions, while the larger, heat-sensitive ribozyme accumulates in the cooler regions, and is protected from melting. Indeed, the researchers were astonished to discover that the ribozyme molecules aggregated to form larger complexes, which further enhances their concentration in the colder region. In this way, the lifetimes of the labile ribozymes could be significantly extended, in spite of the relatively high temperatures. "That was a complete surprise," says Braun.
The lengths of the replicated strands obtained are still comparatively limited. The shortest RNA sequences are more efficiently duplicated than the longer, such that the dominant products of replication are reduced to a minimal length. Hence, true Darwinian evolution, which favors synthesis of progressively longer RNA strands, does not occur under these conditions. "However, based on our theoretical calculations, we are confident that further optimization of our temperature traps is feasible," says Braun. A system in which the ribozyme is assembled from shorter RNA strands, which it can replicate separately, is also a possible way forward.
rational experiences
Veteran Member
When humans claim I am comparing my life. 2 adult human being parents, with sperm and an ovary who have sexual intercourse for any human to be an observer, from a fully owned and living human being life is why the argument about God O the circle of life was stated.
If a scientist compared what I own and how I live to DNA/RNA strand in the bodies of mass that they study, then by artificial comparison they would then try to remove us from the natural form that we live owning. Seeing we do not exist as a human life in any of those forms, rationally.
So you would wonder at why a living conscious human being would claim it was their human beginnings, yet science does make those types of claims.
Humans gave a very simple explanation of self human bio life human presence in a God theme, how the gases burning/cooling in a spatial vacuum, sitting upon the face of water, due to evaporation in a light heavenly body was why life was actually alive and living. In a rational use of human self bio conscious statement for self continuance versus fake comparisons off mass against natural form.
Why that type of scientific thinking was once quantified as Satanic for the forms of their studies involve burning mass bodies.
If a scientist compared what I own and how I live to DNA/RNA strand in the bodies of mass that they study, then by artificial comparison they would then try to remove us from the natural form that we live owning. Seeing we do not exist as a human life in any of those forms, rationally.
So you would wonder at why a living conscious human being would claim it was their human beginnings, yet science does make those types of claims.
Humans gave a very simple explanation of self human bio life human presence in a God theme, how the gases burning/cooling in a spatial vacuum, sitting upon the face of water, due to evaporation in a light heavenly body was why life was actually alive and living. In a rational use of human self bio conscious statement for self continuance versus fake comparisons off mass against natural form.
Why that type of scientific thinking was once quantified as Satanic for the forms of their studies involve burning mass bodies.