[HN Gopher] The Chiral Puzzle of Life
___________________________________________________________________
The Chiral Puzzle of Life
Author : bookofjoe
Score : 47 points
Date : 2020-05-24 20:07 UTC (2 hours ago)
(HTM) web link (iopscience.iop.org)
(TXT) w3m dump (iopscience.iop.org)
| prvc wrote:
| >a small, but persistent, chiral bias
|
| >If this mechanism dominates, then the handedness of living
| systems should be universal.
|
| No matter how large the bias (unless it's "astronomically" close
| to 1), there will be, by the law of large numbers, some world
| populated by life of the opposite chirality to the favoured one,
| due to it arriving first there, given the size of the universe.
| 6nf wrote:
| Yup I don't think the author meant that all life in the entire
| universe must be the same chirality, just that the bias would
| be widespread across the universe
| aazaa wrote:
| The origin of homochiral building blocks (amino acids, sugars) is
| certainly an old mystery. But it doesn't seem to be a very deep
| one. By that I mean that there are many physical processes that
| could have initially led to a small preference. Natural selection
| then would do the rest.
|
| The deeper mystery is how self-replicating chemical systems ever
| came about in the first place. There are several fairly steep
| hurdles to overcome, and so far nobody has put forward a
| compelling, testable hypothesis leading from the "primordial
| soup" to anything even distantly resembling the simplest
| organisms.
| kleer001 wrote:
| RNA-world seems pretty compelling to me.
|
| Self replication and catalysis. That sounds like enough to go
| on.
| api wrote:
| There are many hypotheses but they are quite hard to test. The
| problem is that any such process is likely to have involved
| millions of years (at a minimum) of essentially random search
| among initial building blocks before something "takes."
|
| How do you even try to replicate that? We could perhaps fast
| forward it in a lab but that is going to make it contrived.
|
| The best we can probably do is to work backward from the
| simplest life to a credible model of prebiotic replicating
| molecular systems and then back from there to random organics
| plus energy. Then try to do isolated experiments to assign
| probability bounds and then try to estimate time and
| probability. This is not a true replication or a direct
| observation but it could at least provide a credible model.
| TeMPOraL wrote:
| I remember a coherent-sounding (to a somewhat smart layman)
| theory being presented in "The Vital Question". It involved
| alkaline vents (like these: [0]). As I remember it, the idea
| was that the nonviolent flow of matter and the porous rock of
| the vent created a natural chemical reactor, where gunk could
| accumulate in the pores, until it slowly chanced into a
| primitive pump, primitive membrane and primitive division;
| eventually, some of that gunk learned how to close a membrane
| around itself, with stuff from the alkaline vent on the
| inside, and could now survive out in the open, continuously
| pumping to keep the gradient. Evolution continued from there.
|
| --
|
| [0] -
| https://en.wikipedia.org/wiki/Lost_City_Hydrothermal_Field
| sova wrote:
| Is it not pure speculation to assume that the world was present
| before living beings inhabited it? Who made these observations
| of a purely physicalist realm that predates beings with
| awareness? It may be true, but its unconfirmable, so we have to
| ask questions about what we can confirm. Chirality in the
| present is confirmable. A world made of physical matter and
| mind is confirmable. But strong questions about ontological
| declarations of life from purely physicalist material
| speculative histories are not only hard to answer, they assume
| more than they reveal. Edit: must have hit a
| nerve
| [deleted]
| dvt wrote:
| I don't think you hit a nerve; your post is not only
| confusing, but it seems wrong.
|
| > Is it not pure speculation to assume that the world was
| present before living beings inhabited it?
|
| You need to carefully define terms here. What do you mean by
| "world," what do you mean by "living beings," and what do you
| mean by "inhabited." In any case, the answer to the question
| you pose is almost certainly answerable in the negative.
|
| > But strong questions about ontological declarations of life
| from purely physicalist material speculative histories are
| not only hard to answer, they assume more than they reveal.
|
| I'm not a materialist, but this isn't correct. In fact, a
| major criticism of physicalism is that it's _too reductive_
| -- not that it has no explanatory power. It has a lot of it;
| that 's partly why most professional philosophers are
| materialists.
| peter303 wrote:
| Perhaps there is slightly slightly different ground energy state
| of the two different chiralities and Nature selected the slightly
| lower one. I have not seen evidence supporting this hypothesis.
|
| A similar mystery is why DNA chose a base64 nucleic coding system
| for 21 amino acids and a few punctuations. Some of the codons are
| redundant and some unused. (There appears to be a fossil base16
| coding system inside it.) And synthetic biologists have modified
| it into a working base216 system with additional nucleic acids
| and amino acids. Perhaps again there is some ground energy
| argument as to why this universal 3-billion year old coding
| system is as complex as it is and no more complex.
| fqrley wrote:
| Asimov wrote a book on the subject:
| https://en.wikipedia.org/wiki/The_Left_Hand_of_the_Electron
| philsnow wrote:
| There's a bit of a callout to the handed chirality of life on
| Earth in Daniel Suarez' "Change Agent"
| https://www.amazon.com/Change-Agent-Daniel-Suarez/dp/1101984...
|
| Like all of his books, it's a quick read that feels a bit like a
| movie screenplay. Fast and fun, each book of his has a well-
| enough-developed hook, but overall I liked Daemon and Freedom
| best.
| djaque wrote:
| That's a really interesting idea that cosmic rays caused the
| chiral asymmetry. Any biologists want to chime in on how this
| fits in with other ideas on the problem?
| [deleted]
___________________________________________________________________
(page generated 2020-05-24 23:00 UTC)