Post n.3 Recent publications
At the
beginning of the 1980s, Mario Ageno, in Lectures on Biophysics, after examining
the thought of Oparin and Haldane and the ideas of Sidney Fox, Harada, Herrera
and Calvin, wrote: "What we have said so far about the so-called
'theories' of the origin of life, proposed over the last fifty years and in
part still enjoying a certain amount of credit among some, is sufficient to
demonstrate the futility of this race to see who is the cleverest and most
brilliant in the hunt for ideas. It is clear that these ideas are always
patently inadequate in the face of the complexity of the problem, even if they
can sometimes help to illuminate some very particular aspect of it. In order to
acquire substantial and lasting results, one must set out on a different path:
that of the patient collection of clues, of the testimonies still present in
today's world of life, of their critical elaboration into coherent hypotheses
and of a continuous comparison of these hypotheses with the 'experiment'.
Well, one of
the evidences still present is that life is asymmetrical. How did the amino
acids Destro and Levo separate? Why was Ribose Right and not Ribose Levo
chosen? And why were only 20 of the many
amino acids present in prebiotic times chosen and why those? And how did the
genetic code originate?
Solving these
problems requires years of work and so we fall back on the brilliant idea, in
the hope that it might help to shed some light on some very particular aspects.
I do not know
how the processes of self-promotion of molecules were discovered. I have always
known that if a chemical-physical process takes place, it is because it
decreases its energy (technically its free energy).
The article
contains some publications of the last
20 years. Source: Le Scienze online.
From interstellar clouds the first molecules for life
on Earth
by Yasemin Saplakoglu/Quanta
Magazine
A laboratory experiment has successfully reproduced a mechanism by which parts of proteins could have formed spontaneously on cosmic dust, suggesting their role in the early stages of the origin of life, on our planet or elsewhere
Perhaps at the origin of life there was a hybrid of
RNA and protein
by Davide
Castelvecchi/Nature
According to
the standard theory, in an RNA world, life may have existed in the form of
complex proto-RNA strands capable of copying themselves and competing with
other strands. Later, these 'RNA enzymes' might have developed the ability to
build proteins and eventually transfer their genetic information into a more
stable DNA. How this could have happened was an open question, partly because
catalysts made of RNA alone are much less efficient than the protein-based
enzymes found in all living cells today. 'Although [RNA]-based catalysts have
been discovered, their catalytic power is poor,' says Thomas Carell, an organic
chemist at the Ludwig Maximilian Universität in Munich, Germany. [...]
Carell's team
constructed a synthetic RNA molecule that includes two modified nucleosides by
joining two pieces of RNA commonly found in living cells. At the first of the
exotic sites, the synthetic molecule could bind to an amino acid, which then
moved laterally to bind to the second adjacent exotic nucleoside. The team then
separated the original RNA strands and inserted a new one with its own amino
acid. This was in the correct position to form a strong covalent bond with the
amino acid previously attached to the second strand. The process continued step
by step, growing a short chain of amino acids - a mini-protein called a peptide
- that attached itself to the RNA. The formation of bonds between amino acids
requires energy, which the researchers provided by priming the amino acids with
various reagents in the solution
Loren
Williams, a chemist-biophysicist at the Georgia Institute of Technology in
Atlanta, agrees. "If the origins of RNA and proteins are linked and their
emergence is not independent, then the maths shifts radically in favour of an
RNA-protein world and not an RNA world," he says.
18 January 2021
Primordial life and the threat of water
by Michael
Marshall/Natur
Water is
indispensable for survival, but for the development of early life it posed a
very serious threat because it can break down DNA and other essential
molecules. How was this apparent paradox overcome? The solution was small pools
in which water was intermittently present.
Emerging
evidence led many researchers to abandon the idea that life appeared in the
oceans, and to focus instead on land-based environments, in places that were
now dry and now wet. This shift in perspective is not shared by all, but
scientists in favour of the idea of a beginning on land argue that it solves a
long-known paradox: water is essential for life, but also destructive to its
main components.
From an asteroid energy and ingredients for the origin
of life
A simulation
of the primordial Earth hit by an asteroid shows that fundamental compounds
such as amino acids can be produced in mixtures of simple inorganic compounds
such as iron, nickel, water, as well as nitrogen and carbon dioxide, thanks to
the energy released by the impact (Red.)
Did life originate from a genetic hybrid?
by Andy
Extance/Scientific American
A new
experiment that attempted to recreate conditions on the primordial Earth
suggests that RNA and DNA, the molecules that contain genetic information, may
have formed at the same time. The result contrasts with the 'RNA world'
hypothesis, according to which RNA was the precursor to DNA, a popular theory
but one that has yet to be fully convinced.
Cosmic rays and the shape of life
by Charlie
Wood/Quanta Magazine
It is one of
the great unsolved mysteries of biology: why in all living organisms are the
DNA and RNA helices always wound only to the right? According to two
astrophysicists, it may have been cosmic rays in the early stages of life's
history that gave an evolutionary advantage to this particular structure of the
molecules containing the genetic information
The origins of metabolism at the dawn of life
by John
Rennie/Quanta Magazine
The chemical reactions that characterise cell metabolism today are extremely complex. A study has now found that their ancestral, much simpler versions could have taken place as early as the 'primordial soup' from which life originated, to become progressively more sophisticated over the course of evolution
Even Mansy,
despite his enthusiasm for this work, is cautious about interpretation.
'Metabolism,' he explains, 'is not just about the formation of constituent
parts. Rather, it is a kind of energy flow that maintains the low entropy state
of a cell'. According to him, evidence that some form of proto-metabolism
helped the precursors of cells to survive better (even if, strictly speaking,
those precursors were not really alive) is still lacking, among other things. 'Until
we start to understand how these kinds of chemical reactions can give a
selective advantage to one encapsulated chemical system over another,' he
comments, 'I don't know where this is leading us.
An artificial primordial soup to support the RNA world
by Davide
Castelvecchi/Nature
A laboratory
experiment has demonstrated a chemical pathway that produces the four bases of
ribonucleic acid under conditions similar to those on the primordial Earth,
reinforcing the hypothesis that the first life forms on the planet were based
on this molecule
An alternative hypothesis on the origin of life
by Martina
Saporiti
The oceans
would not have been the crucible of chemical reactions from which life arose,
but small bodies of water. New research reinforces a hypothesis already put
forward by Darwin
A new ingredient fundamental to life
(Science Photo Library / AGF)
The
composition of the earliest RNAs that marked the transition from the simplest
chemicals to the earliest forms of life on Earth may have been slightly
different than that of current RNAs(red)
RNA and the origin of life
© Science Photo Library / AGF
Created for
the first time is a ribozyme - an RNA strand that functions like an enzyme -
capable of self-replication, as it can also make a copy of folded RNAs, and not
just linear ones. A point in favour of the hypothesis that life originated in
an 'RNA world'(red)
by Milena
Castigli September 8, 2017
The primordial
soup that gave rise to life on Earth did not need any 'flaming' to form the
first proteins, but only the continuous bubbling of hundreds of precursor
molecules, joined together by reactions very common in those primitive
environmental conditions.
The
researchers recreated the primordial soup in the laboratory using mainly amino
acids and hydroxy acids, the most abundant ingredients at that time.
The scientists
were thus able to observe that against all odds the elements came together like
bricks, spontaneously forming the precursors of proteins: the depsipeptides.
Their evolution was then accelerated by 'drying' them at 85 degrees and
throwing them back into the broth, in order to simulate the cyclical process
that depsipeptides might have undergone when the puddles on Earth dried out and
filled with water again.
Without any
effort, the first peptides were thus obtained whose chains, joined and folded,
go on to form proteins. The study was published in the journal of the American
Academy of Sciences (Pnas). Source: Ansa.
A new theory on the origin of life
It would have
been the combined action of peptides and ribonucleic acid (RNA) that triggered
the processes from which life on Earth originated. This is supported by a new
theory that challenges the so-called RNA world hypothesis, according to which
ribonucleic acid alone was sufficient to trigger life. (Red)
28 July 2015
Self-replication and the origin of life
A new model
explains how increasingly complex polymers capable of self-replication may have
developed from simple molecules. The model may fill gaps in the explanation of
how life arose from the primordial soup in which the first organic molecules
formed
9 September
2014
A step forward in explaining the origin of life
© Robert Postma/First Light/Corbis
Sophisticated computer simulations of Stanley Miller's classic experiments on the formation of complex organic compounds from simple molecules in the 'primordial soup' of the ancient Earth have shown the central role of electric fields in the environment. The result indirectly strengthens the 'RNA world' theory and has interesting implications for the search for extraterrestrial life forms(red)
Particularly
significant is the explanation for the formation of formamide, as it has
recently been shown that this molecule, when subjected to UV irradiation,
allows the formation of guanine. Guanine was the only one of the four
nucleotide bases that could not be produced merely by providing heat to the
'primordial soup', so much so that scholars of the origin of life had dubbed
guanine 'the missing G'.
An even richer 'primordial soup
Jeffrey Bada, rediscovered samples of the
results of Miller's 1958 experiments, and subjected them to new analysis, first
in 2008, already finding more amino acids than originally identified by Miller,
and then again recently, obtaining results that indicate that the variety of
organic compounds present in Earth's distant past was much greater than
previously thought, and also found that the amino acids produced in Miller's
hydrogen sulphide experiment are similar in structure and ratio to those found
in meteorites, a result that supports the hypothesis that processes such as
those in these experiments are widespread in the universe.
03 February 2010
A theory against the 'primordial soup
Thermodynamic constraints imply that chemosynthesis is strictly necessary for carbon and energy metabolism in all organisms growing from simple chemical compounds, and presumably it was also necessary in the first cells capable of autonomous life. The textbooks recite that life originated from the primordial soup in which the first cells formed by fermenting the organic substances present therein to generate energy in the form of ATP; we provide an alternative theory that life originated from gases, H2, CO2, N2, and H2S, and that the energy for the earliest forms of life came from exploiting the geochemical gradients present in the ocean floor in hydrothermal springs, probably interconnected by a myriad of compartments or pores.
Was the primordial atmosphere reducing?
Experiments
with chondrites suggest that the atmosphere of the early Earth was devoid of
oxygen and rich in methane and ammonia
Using
primitive meteorites (chondrites) as a model, a team of geophysicists and
planetary scientists at Washington University in St. Louis performed outgassing
calculations and showed that Earth's primordial atmosphere was reductive, full
of methane, ammonia, hydrogen and water vapour
Did life originate from a mineral?
Some of the
initial processes that helped form life on Earth are said to be due to a
mineral containing borax
Life flourishing at the bottom of the oceans
by Cindy Lee
Van Dove/Nature
The importance
of microbial chemosynthesis near hot springs also prompts us to rethink our
ideas about the extreme conditions life can adapt to, the origin of life on this
planet and also the potential for life elsewhere in the universe.
Life
from rocks
The first living beings formed from the only
available raw materials: air, water and rock.
A series of fascinating experiments is revealing
that minerals play a crucial part in the basic chemical reactions from which
life must have originated.
The
left hand of life
Life's preference for left-handed molecules
could be the result of its own self-promotion
In a study published in the journal 'Nature',
researchers describe their experiment in which they used peptides, chains made
up of a few amino acids, to understand why life is dominated by homochirality.
The peptides used in the experiments could be combined to give rise to four
different products, two homochiral, composed only of left or right-handed amino
acids, and two heterochiral, composed of peptides of different orientations.
After mixing their peptides, the researchers
almost always obtained homochiral products and observed that this occurs
because homochiral molecules, once produced, tend to stimulate the production
of those similar to them, a behaviour not observed in heterochiral molecules.
Life-bearing
giants
Only solar systems like ours, where giant
planets are found, can harbour life
According to the results of a recent study, the
search for life on other worlds should focus on solar systems similar to our
own with giant planets. In fact, it seems that it was Jupiter that 'shipped'
the water necessary for carbon-based life to Earth.
Next Post: Life
beyond the Earth. (end of october-november)
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