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This is huge news if true for evaluating soil experiments on Mars. They could give false positives for life if they only look for metabolic products.

by emsign 4mo ago

cogman10 4mo ago
Not as much as you might think. We've found amino acids almost everywhere we look, including astroids [1]. It seems that the building blocks of life pretty naturally and readily form. Which is a pretty strong indicator that life is likely fairly common outside earth. [1] https://www.nasa.gov/news-release/nasas-asteroid-bennu-sample-reveals-mix-of-lifes-ingredients/ https://www.nasa.gov/news-release/nasas-asteroid-bennu-sampl...
- stevenwoo 4mo ago
  Tangentially related, this is a bit trying to sell upcoming book, but the discussion of origins of life was interesting to me. https://www.newscientist.com/article/2526959-how-a-radical-new-view-of-life-could-reveal-its-origin-and-aliens/ https://www.newscientist.com/article/2526959-how-a-radical-n... YMMV but It’s free via my local library and Libby if you are stopped by the subscription nag.
- adrian_b 4mo ago
  The amino acids that can be found everywhere include ten of the simpler amino-acids that are used in proteins (glycine, the 2 acids, the 3 branched, alanine, proline and the 2 alcohols). The other 11 amino-acids from proteins have never been found where life does not exist. They are more complex and they seem to have been developed by living beings long after the appearance of life and the appearance of the genetic code (they seem to have substituted later the simpler amino-acids in certain locations of the map of the original genetic code, which encoded fewer amino-acids). Moreover, while the simple amino-acids, including the ten that are used in proteins, can be found pretty much everywhere, wherever they were not produced by living beings they have been found in racemic mixtures, i.e. in equal amounts of left-handed and right-handed isomers, while in proteins only the left-handed isomers are used, so the living beings normally produce almost only left-handed isomers. Very small quantities of right-handed isomers are produced by some living beings, for other purposes than making proteins. So it is relatively easy to distinguish amino-acids that have been produced by living beings from amino-acids that have been produced in abiotic conditions (i.e. the amino-acids produced in abiotic conditions are recognized by the absence of complex amino-acids and by the presence of great quantities of right-handed isomers).
  - asdff 4mo ago
    I don't see the left handed aspect as necessary for life. To me this just suggests our common ancestor for life on earth made use of this chirality. Another group of organisms somewhere else could have evolved from an ancestor that makes use of right handed chirality. Or one that is hand-blind.
    - adrian_b 4mo ago
      I agree. It seems that the choice between left-handed and right-handed amino-acids was random. However, it is unlikely that other kinds of life forms could use both kinds indiscriminately, because mixing them creates difficulties in the assembling of polymers. So it is likely that amino-acids produced by some extra-terrestrial life form would also be predominantly of only one orientation, but it could happen to be the right-handed variant. Moreover, extra-terrestrial life forms could use very different complex amino-acids, because there are much more of those than the 11 that have been added to the simple amino-acids in the terrestrial proteins.
      - asdff 4mo ago
        That makes sense that the chirality can affect downstream polymer assembly or even folding in the higher order structures. Likely we are all left handed on earth because our left handed ancestor outcompeted the right handed organisms in the primordial soup. Or the right handed organisms just didn't evolve in the first place here on earth and there was nothing to outcompete. There might still be some higher order advantages to shifting chirality one way or another. Certain molecules, such as methamphetamine, have differing bioactivity based on chirality. Maybe this can be regulated in some way such as to control the rate of some other downstream process. In an abstracted sense, chemists here on earth are already this organism as they refine reactions to produce desired chirality and reduce expenditure on undesired chirality. ET could be using different amino acids, or more or fewer. I would hazard to guess there is immense selection to reduce the amino acid set to its most necessary components. This pressure has gotten to the point here on earth where even these necessary components might not all be produced endogenously by the organism who needs them, but consumed from the environment saving energy spent on synthesis. But this requires your neighbor to be producing these AAs, such that you consume them, and you having sufficient feedback mechanisms to not immediately consume all of your neighbor's species and put your own insufficient lineage to extinction.
adrian_b 4mo ago
In the second part of the article there is an explanation which for me is the most plausible, and which would not be applicable to Martian soil. Even if they killed all living beings in the soil, after their death the enzymes that are the catalysts for metabolism would just become dispersed in the soil and they continue to catalyze reactions like those of the Krebs cycle. After many years of storage the molecules of the enzymes will be degraded, i.e. they will break into fragments. That again does not mean much, because the catalytic action of the enzymes is typically caused by very small parts of the enzymes, which can remain intact even after fragmentation. In general, the biggest part of an enzyme is just a scaffold that attaches the enzyme in precise places of a cell, usually on some intracellular membranes, so that a great number of enzymes can be assembled like a production line in a factory, to coordinate the metabolic reactions for maximum efficiency. After death and enzyme fragmentation, even after many years, the catalytic fragments of the enzymes can still catalyze reactions like those of the Krebs cycle. It is also possible that some of the observed chemical reactions are catalyzed by minerals present in the soil and not by remnants of the enzymes from the dead cells, but for now no evidence has been gathered about this. Moreover, there are enzyme residues which are difficult to distinguish from abiotic minerals. Some of the enzymes involved here contain a catalytic part formed by a cluster of iron and sulfur atoms, which are attached to a protein molecule. That iron-sulfur cluster is pretty much identical with a very small fragment of an iron sulfide mineral.

This is huge news if true for evaluating soil experiments on Mars. They could give false positives for life if they only look for metabolic products.

by emsign 4mo ago

This is huge news if true for evaluating soil experiments on Mars. They could give false positives for life if they only look for metabolic products.

cogman10 4mo ago

Not as much as you might think. We've found amino acids almost everywhere we look, including astroids [1]. It seems that the building blocks of life pretty naturally and readily form. Which is a pretty strong indicator that life is likely fairly common outside earth. [1] https://www.nasa.gov/news-release/nasas-asteroid-bennu-sample-reveals-mix-of-lifes-ingredients/ https://www.nasa.gov/news-release/nasas-asteroid-bennu-sampl...

stevenwoo 4mo ago
Tangentially related, this is a bit trying to sell upcoming book, but the discussion of origins of life was interesting to me. https://www.newscientist.com/article/2526959-how-a-radical-new-view-of-life-could-reveal-its-origin-and-aliens/ https://www.newscientist.com/article/2526959-how-a-radical-n... YMMV but It’s free via my local library and Libby if you are stopped by the subscription nag.
adrian_b 4mo ago
The amino acids that can be found everywhere include ten of the simpler amino-acids that are used in proteins (glycine, the 2 acids, the 3 branched, alanine, proline and the 2 alcohols). The other 11 amino-acids from proteins have never been found where life does not exist. They are more complex and they seem to have been developed by living beings long after the appearance of life and the appearance of the genetic code (they seem to have substituted later the simpler amino-acids in certain locations of the map of the original genetic code, which encoded fewer amino-acids). Moreover, while the simple amino-acids, including the ten that are used in proteins, can be found pretty much everywhere, wherever they were not produced by living beings they have been found in racemic mixtures, i.e. in equal amounts of left-handed and right-handed isomers, while in proteins only the left-handed isomers are used, so the living beings normally produce almost only left-handed isomers. Very small quantities of right-handed isomers are produced by some living beings, for other purposes than making proteins. So it is relatively easy to distinguish amino-acids that have been produced by living beings from amino-acids that have been produced in abiotic conditions (i.e. the amino-acids produced in abiotic conditions are recognized by the absence of complex amino-acids and by the presence of great quantities of right-handed isomers).
- asdff 4mo ago
  I don't see the left handed aspect as necessary for life. To me this just suggests our common ancestor for life on earth made use of this chirality. Another group of organisms somewhere else could have evolved from an ancestor that makes use of right handed chirality. Or one that is hand-blind.
  - adrian_b 4mo ago
    I agree. It seems that the choice between left-handed and right-handed amino-acids was random. However, it is unlikely that other kinds of life forms could use both kinds indiscriminately, because mixing them creates difficulties in the assembling of polymers. So it is likely that amino-acids produced by some extra-terrestrial life form would also be predominantly of only one orientation, but it could happen to be the right-handed variant. Moreover, extra-terrestrial life forms could use very different complex amino-acids, because there are much more of those than the 11 that have been added to the simple amino-acids in the terrestrial proteins.
    - asdff 4mo ago
      That makes sense that the chirality can affect downstream polymer assembly or even folding in the higher order structures. Likely we are all left handed on earth because our left handed ancestor outcompeted the right handed organisms in the primordial soup. Or the right handed organisms just didn't evolve in the first place here on earth and there was nothing to outcompete. There might still be some higher order advantages to shifting chirality one way or another. Certain molecules, such as methamphetamine, have differing bioactivity based on chirality. Maybe this can be regulated in some way such as to control the rate of some other downstream process. In an abstracted sense, chemists here on earth are already this organism as they refine reactions to produce desired chirality and reduce expenditure on undesired chirality. ET could be using different amino acids, or more or fewer. I would hazard to guess there is immense selection to reduce the amino acid set to its most necessary components. This pressure has gotten to the point here on earth where even these necessary components might not all be produced endogenously by the organism who needs them, but consumed from the environment saving energy spent on synthesis. But this requires your neighbor to be producing these AAs, such that you consume them, and you having sufficient feedback mechanisms to not immediately consume all of your neighbor's species and put your own insufficient lineage to extinction.

adrian_b 4mo ago

In the second part of the article there is an explanation which for me is the most plausible, and which would not be applicable to Martian soil. Even if they killed all living beings in the soil, after their death the enzymes that are the catalysts for metabolism would just become dispersed in the soil and they continue to catalyze reactions like those of the Krebs cycle. After many years of storage the molecules of the enzymes will be degraded, i.e. they will break into fragments. That again does not mean much, because the catalytic action of the enzymes is typically caused by very small parts of the enzymes, which can remain intact even after fragmentation. In general, the biggest part of an enzyme is just a scaffold that attaches the enzyme in precise places of a cell, usually on some intracellular membranes, so that a great number of enzymes can be assembled like a production line in a factory, to coordinate the metabolic reactions for maximum efficiency. After death and enzyme fragmentation, even after many years, the catalytic fragments of the enzymes can still catalyze reactions like those of the Krebs cycle. It is also possible that some of the observed chemical reactions are catalyzed by minerals present in the soil and not by remnants of the enzymes from the dead cells, but for now no evidence has been gathered about this. Moreover, there are enzyme residues which are difficult to distinguish from abiotic minerals. Some of the enzymes involved here contain a catalytic part formed by a cluster of iron and sulfur atoms, which are attached to a protein molecule. That iron-sulfur cluster is pretty much identical with a very small fragment of an iron sulfide mineral.