Learning chemical networks give life a chiral twist
Chirality preference in a living matter may arise spontaneously to
optimize energy harvesting

Date:
April 26, 2022
Source:
Institute for Basic Science
Summary:
A study shows that the preference of biological molecules for left
or right-handedness -- a hallmark of living matter -- could emerge
spontaneously as prebiotic chemical networks adapt to optimize
energy harvesting. The proposed mechanism of symmetry breaking is
general and can apply to other transitions in living matter that
lead to increased complexity.



FULL STORY ==========================================================================
When holding a right hand in front of a mirror, one can see a reflected
image of a left hand and vice versa. In 1848, Louis Pasteur discovered
that organic molecules are much like our hands: they come in mirror-image
pairs of left- and right-handed variants. Nowadays, we know that this handedness or chirality (from the Greek word for "hand") is a hallmark
of organic molecules.


========================================================================== Organic molecules are rich in carbon atoms, which form bonds to create
either a right or a left "nano-hand." Yet, puzzlingly, life almost
always selects to exclusively use one of the two mirror-image twins --
a phenomenon called homochirality. For example, terrestrial life is
based on left-handed amino acids and right-handed sugars.

While many explanations were suggested, how and why homochirality
emerged remains an enigma. Chiral symmetry breaking, which is a
phenomenon where a 50- 50 ratio mixture of left and right-handed
molecules departs to favor one over the other, is of great research
interest in biochemistry. Understanding the origin of homochirality is
highly important for investigating the origin of life, as well as more practical applications such as the synthesis of chiral drug molecules.

* A model proposes a novel explanation for the emergence of
homochirality
in life -- a longstanding puzzle about the origin of life on Earth.

It is widely believed that life originated in habitats rich in energy
sources - - such as hydrothermal vents in the depths of primordial
oceans. Considering possible primordial Earth scenarios, Prof. Tsvi Tlusty
and Dr. William Pin~eros from the Center for Soft and Living Matter within
the Institute for Basic Science, South Korea, envisioned a complex network
of chemical reactions that exchange energy with the environment. When
the team used a mathematical model and system simulation to emulate a well-stirred solution of different chemical elements in a container,
they surprisingly found out that such systems naturally tend to break
the molecular mirror symmetry.

* Homochirality emerges spontaneously in prebiotic chemical networks
that
adapt to optimize energy harvesting from the environment.

Previously it was believed that chiral symmetry breaking requires multiple loops of auto-catalysis, which increasingly produces one enantiomer of
a molecule while inhibiting the formation of the other. However, the
IBS team's results showed that the underlying mechanism of symmetry
breaking is very general, as it can occur in large reaction systems
with many random molecules and does not require sophisticated network architectures. It was found that this sharp transition to homochirality
stems from the self-configuration of the reaction network in order to
achieve more efficient harvesting of energy from the environment.

The model developed by Pin~eros and Tlusty showed that highly-dissipating systems and large energy differences are more prone to inducing chiral
symmetry breaking. Furthermore, the calculations revealed that such
transitions are almost inevitable, so it is reasonable to believe they
may generically occur in random chemical reaction systems. Thus, the
energy harvesting optimization- based model demonstrated by the group
explains how homochirality could have spontaneously arisen from the harsh, energy-rich environment of the early planet Earth.

* The proposed mechanism of symmetry breaking is a general one and can
apply to other transitions in living matter that lead to increased
complexity.

Moreover, the model proposes a general mechanism that explains how
the complexity of a system can grow as it better adapts to exploit a
varying environment. This suggests that chiral symmetry breaking is an
inherent hallmark of any complex system (such as life) that is capable
of configuring itself to adapt to an environment. These findings may furthermore explain spontaneous symmetry breakings in much more complex biological processes, such as cell differentiation and the emergence of
new genes.

This study was published in the journal Nature Communications.


========================================================================== Story Source: Materials provided by Institute_for_Basic_Science. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. William D. Pin~eros, Tsvi Tlusty. Spontaneous chiral symmetry
breaking in
a random driven chemical system. Nature Communications, 2022; 13
(1) DOI: 10.1038/s41467-022-29952-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220426101707.htm

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