Chirality (Introduction)
by David Turell 
, Wednesday, November 30, 2011, 16:17 (4922 days ago)
An excellent review of the problem of chirality; all essential amino acids are left-handed.
The article has no answers, only negative findings:
http://sandwalk.blogspot.com/2009/04/can-watery-asteroids-explain-why-life.html
Chirality; new findings
by David Turell , Tuesday, December 17, 2019, 18:38 (1982 days ago) @ David Turell
Another new study of chirality:
https://phys.org/news/2019-12-corkscrew-lasers-chiral-molecules.html
"Many of the molecular building blocks of life have two versions that are mirror images of one another, known as enantiomers. Although seemingly identical, the two enantiomers can have completely different chemical behaviour—a fact that has major implications in our day-to-day lives. For example, while one version of the organic compound carvone smells like spearmint, the mirror form smells like caraway seed. In pharmacology and drug design it can be essential to be able to distinguish between the two enantiomers and separate them if necessary, since the consequences can be life-changing. For instance, while one enantiomer of beta blockers selectively targets the heart, the other acts only on the cell membranes of the eye.
***
"Molecules that exist in mirror versions of each other are called chiral after the Ancient Greek word for hand, referring to the fact that the right and left hand are mirror versions of each other. For so-far unknown reasons, life often favors one version: While proteins are almost always left-handed, sugars are usually right-handed. (my bold)
"'Traditionally, chiral analysis has been restricted to liquids but we are seeing a growing rise in gas-phase methods as they offer far greater sensitivity," says DESY scientist Andrey Yachmenev, lead author of the study. "The ability to cool gases down close to absolute zero affords us better control of our sample, and this in turn can be exploited to efficiently separate the enantiomers and produce higher yields of one enantiomer instead of the other."
"At the heart of their approach is a specially designed laser-setup composed of an optical centrifuge, a corkscrew-shaped laser pulse that can spin molecules incredibly fast, over a trillion times per second. When combined with an additional electric field, the entire setup becomes chiral and the two enantiomers behave differently, displaying unique quantum dynamics.
"'The interaction of the laser field with a chiral molecule creates what we call a field-induced diastereomer," explains co-author Emil Zak from DESY. Diastereomers are different configurations of the same compound that are not mirror versions of each other. The distinct characteristics of diastereomers can be utilized to separate the enantiomers in space.
***
"The scheme has been computationally demonstrated on the prototypical chiral molecule propylene oxide (C3H6O), which was incidentally also the first complex organic chiral molecule to be detected in interstellar space. Efforts are now underway to perform experiments at DESY and capitalize on the electrostatic deflection techniques pioneered in the Controlled Molecule Imaging group led by Jochen Küpper at the Center for Free-Electron Laser Science CFEL, a joint institution of DESY, Max Planck Society, and Universität Hamburg.
"'Manipulating chiral molecules in the gas-phase is undergoing a period of exciting development, both for practical applications used in industry, and for providing new insights into what is a very fundamental aspect of nature," says Yachmenev. "The origin of chirality and life's handedness is one of the great mysteries, but we are gradually getting closer to a deeper and more complete understanding.'"
Comment: We do not understand why chirality makes for different functions although we certainly recognize that protein shape makes fur specific function. Chirality makes origin of life not a result of chance. Why are amino acids left handed and sugars right handed?
Chirality; new findings
by David Turell , Wednesday, May 14, 2025, 18:23 (8 days ago) @ David Turell
Handedness defines function:
https://www.quantamagazine.org/how-the-universe-differs-from-its-mirror-image-20250514/
"Louis Pasteur discovered while experimenting with some expired wine that certain molecules can be chiral. They can come in distinct left-handed and right-handed structural forms that are impossible to superimpose. Pasteur found that, while they contain all the same components, the mirror versions of chiral molecules can serve distinct chemical functions.
***
"Lactose, the sugar found in milk, is chiral. While either version can be synthesized, the sugars produced and consumed by living organisms are always the right-handed ones. In fact, life as we know it uses only right-handed sugars — hence why the genetic staircase of DNA always twists to the right. The root of this “homochirality” remains one of the biggest mysteries clouding the origins of life.
"Worse, if it had contained any bacteria with the opposite handedness, her immune system and antibiotics would have been ill suited to put up a fight. A group of prominent scientists recently cautioned against the synthesis of mirror-image biomolecules(opens a new tab) for this reason — if any were to escape the lab, they could evade every one of life’s defense mechanisms.
***
"Nowadays, physicists consider chirality a fundamental property of all elementary particles, just like charge or mass. The particles that don’t have mass are always traveling at the speed of light, and they also all carry an intrinsic angular momentum as though they’re spinning like a top. If the particles are flying in the direction of your thumb, their spin follows the direction your fingers curl — on either your right hand or your left.
"The situation is a bit more complicated for massive particles, such as electrons and quarks. Because a massive particle travels more slowly, a speedy observer could overtake it and effectively reverse its direction of motion, thus flipping its apparent handedness. For this reason, when describing the chirality of massive particles, physicists often refer to the mathematical description of the particle’s quantum properties. When you rotate a particle, its quantum wave function shifts left or right depending on its chirality.
"Almost every elementary particle has a twin through the looking glass. A negatively charged left-handed electron is mirrored by the anti-positron, a negatively charged right-handed particle.
"Similarly, our universe differs from its mirror image. The weak force — the force that’s responsible for radioactive decay — is felt only by left-handed particles. This means that some particles will decay in the normal world while their counterparts in the mirror would not.
"Plus, there’s one particle that seems not to show up in the mirror at all. The neutrino has only ever been observed in its left-handed form. Particle physicists are investigating whether the right-handed neutrino exists or if neutrinos’ mirror images are simply identical, which could help explain why the universe contains something rather than nothing."
Comment: chirality seems to be the key to everything. That specificity seems designed. Since both handedness types are naturally available why does biochemistry make such choices?
Chirality; new findings
by David Turell , Thursday, May 15, 2025, 18:37 (7 days ago) @ David Turell
Handedness defines function:
https://www.quantamagazine.org/how-the-universe-differs-from-its-mirror-image-20250514/
"Louis Pasteur discovered while experimenting with some expired wine that certain molecules can be chiral. They can come in distinct left-handed and right-handed structural forms that are impossible to superimpose. Pasteur found that, while they contain all the same components, the mirror versions of chiral molecules can serve distinct chemical functions.
***
"Lactose, the sugar found in milk, is chiral. While either version can be synthesized, the sugars produced and consumed by living organisms are always the right-handed ones. In fact, life as we know it uses only right-handed sugars — hence why the genetic staircase of DNA always twists to the right. The root of this “homochirality” remains one of the biggest mysteries clouding the origins of life.
"Worse, if it had contained any bacteria with the opposite handedness, her immune system and antibiotics would have been ill suited to put up a fight. A group of prominent scientists recently cautioned against the synthesis of mirror-image biomolecules(opens a new tab) for this reason — if any were to escape the lab, they could evade every one of life’s defense mechanisms.***
"Nowadays, physicists consider chirality a fundamental property of all elementary particles, just like charge or mass. The particles that don’t have mass are always traveling at the speed of light, and they also all carry an intrinsic angular momentum as though they’re spinning like a top. If the particles are flying in the direction of your thumb, their spin follows the direction your fingers curl — on either your right hand or your left.
"The situation is a bit more complicated for massive particles, such as electrons and quarks. Because a massive particle travels more slowly, a speedy observer could overtake it and effectively reverse its direction of motion, thus flipping its apparent handedness. For this reason, when describing the chirality of massive particles, physicists often refer to the mathematical description of the particle’s quantum properties. When you rotate a particle, its quantum wave function shifts left or right depending on its chirality.
"Almost every elementary particle has a twin through the looking glass. A negatively charged left-handed electron is mirrored by the anti-positron, a negatively charged right-handed particle.
"Similarly, our universe differs from its mirror image. The weak force — the force that’s responsible for radioactive decay — is felt only by left-handed particles. This means that some particles will decay in the normal world while their counterparts in the mirror would not.
"Plus, there’s one particle that seems not to show up in the mirror at all. The neutrino has only ever been observed in its left-handed form. Particle physicists are investigating whether the right-handed neutrino exists or if neutrinos’ mirror images are simply identical, which could help explain why the universe contains something rather than nothing."
Comment: chirality seems to be the key to everything. That specificity seems designed. Since both handedness types are naturally available why does biochemistry make such choices?
Not answered
Chirality; new findings
by David Turell , Wednesday, May 21, 2025, 17:44 (14 hours, 29 minutes ago) @ David Turell
A new study;
https://www.sciencedaily.com/releases/2025/05/250520161843.htm
"By investigating what properties these early membranes may have had, scientists can better understand how life began and evolved into the diversity of organisms we have today.
"An important feature of membranes is what they allow to pass through and what they stop from entering the cell.
"This influences which molecules are involved in the biological processes that keep cells ticking.
***
"The researchers focused on a few types of molecules essential for all life: the sugars that make up the backbone of DNA and RNA and the building blocks of proteins, known as amino acids.
"The researchers were interested in these molecules not only because they are so pervasive across life, but they also twist in specific ways.
***
"In biology, chirality is important for how molecules interact.
"For example, all the sugars in DNA and RNA need to have the same chirality (all be right-handed) to assemble into the backbone of a DNA or RNA strand.
"However, why life chose one chirality over the other has remained a lingering question.
"The researchers propose that early membranes may have played a key part in selecting the right-handed sugars and left-handed amino acids that all life uses today.
"They analyzed what was able to pass through membranes with properties similar to those of archaea, a major group of microbes.
"The researchers also tested a membrane they designed that mixes archaeal and bacterial properties.
"For both types of membranes, the right-handed DNA and RNA sugars more easily passed through, while the left-handed versions had trouble permeating.
"There was more variability among amino acids. Some left-handed amino acids were more likely to pass through the membrane with mixed bacterial and archaeal properties.
"This included the amino acid alanine, which is thought to be one of the first amino acids used by life.
"While this study doesn't paint a complete picture of the amino acids our cells use today, these findings demonstrate how differences in membranes strongly affect which amino acids are able to pass through.
"The authors add, "All known life uses a specific stereochemistry: left-handed amino acids and right-handed DNA. Understanding how this evolved is a long-standing mystery key for understanding the origin of life. Our experiments show that a specific type of membrane -- the structure that encloses cells -- acts as a sieve that selects for the stereochemistry life uses.'"
Comment: still no answers as to why life is so selective in uses of chirality. And it complicates studying origin of life research.