The Thermodynamics of Life

Now I’m a big fan of alternative biochemistry theories in the search for extraterrestrial life. It seems logical to think that given the size of the universe and the number of possible environments out there, life might have found more than one way to organise itself. However, thanks to some clever thermodynamics, it looks quite likely that at least some alien life out there might not be so “alien” after all…

Ever since the famous Miller-Urey experiment, it’s been known that amino acids, the building blocks of proteins, can be formed with relative ease by simple natural processes. In the experiment, 10 of the 20 amino acids used by life were created readily in conditions mimicking the atmosphere of the early planet Earth. Other theories of abiotic amino acid synthesis include interstellar environments such as molecular cloud cores and protostellar disks, as well as hydrothermal vents (though the latter idea is still disputed).

Higgs and Pudritz (McMaster University, Canada), in this paper, show that those same 10 amino acids are created readily, regardless of the source. The reason? Simple thermodynamics! In fact, thermodynamics can predict the order of abundance of those molecules. It can predict it so accurately, in fact, that a nearly exact match is evident between theoretical predictions and the observed abundances in meteorites. There are lots of things that can be debated in most theories regarding life’s origins, but let’s face it; you can’t argue with thermodynamics. It governs chemistry ubiquitously.

It’s likely then, that the earliest proteins used those 10 amino acids, with the others evolving later — in keeping with evolutionary theories. So the question of exactly where life first started has relatively little impact on the chemistry that life would have used. Fascinating.

The implications are profound. And that isn’t a word I use lightly. Simply, if these 10 amino acids were the basis of life on Earth, and they form so favourably, then there’s a very good chance that life on other planets may have originally used the same ten amino acids. The fundamentals of early biochemistry may well be universal! Now that’s exciting!

Of course, there are countless paths life could take from the same humble beginnings. But the fact remains that life here on Earth might have a lot in common with life elsewhere. The differences, I have little doubt, will be so great that we can scarcely imagine… But it’s just possible that the similarities might be equally surprising.

To quote directly from the paper:

Our results also indicate that a certain degree of universality would be expected in the types of organic molecules seen on other earth-like planets. Should life exist elsewhere, it would not be surprising if it used at least some of the same amino acids we do. Simple sugars, lipids and nucleobases might also be shared.

…the combined actions of thermodynamics and subsequent natural selection suggest that the genetic code we observe on the Earth today may have significant features in common with life throughout the cosmos.

ResearchBlogging.orgPaul G. Higgs, Ralph E. Pudritz (2009). A thermodynamic basis for prebiotic amino acid synthesis and the nature of the first genetic code. Astrobiology (accepted) arXiv: 0904.0402

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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22 Responses to The Thermodynamics of Life

  1. invaderxan says:

    Re: Amino Acid Images
    I’m really glad you like them, thank you so much! When I write about molecules (which I do fairly often), I like to have a good visual representation of what it is I’m writing about. With some molecules, the best way to do so, I’ve found, really is to create the images myself. Perhaps I should take commissions…
    Anyway, thanks a lot for your feedback, and if you do have time, I hope you enjoy my blog.

  2. Anonymous says:

    Re: Amino Acid Images
    Thanks very much for replying! :-)
    I think they’re really great images.
    The best I’ve ever seen! (and I’ve seen lots!)
    They’re a brilliant compromise between fully space-filling models (which I do like, but which can be too “full” to easily see how each atom attaches to the others) and ball-and-stick models (which are often too skinny to make a firm impression on the mind).
    I think your serine and proline are just perfect : full enough to make a firm impression – but not too full (and slightly transparent, too!) so that you can very easily see what attaches to what, and where. Brilliant!
    Also, they just look really nice!
    I think they’re wonderful! :-)
    I’d love to see you do more!
    Nice website too.
    I’d like to read around if I get time.
    I found this place on a google image search for amino acid pictures – when(happily) trying “serine” as the search term.
    All the best!

  3. mygxptgp says:

    Perhaps the least unusual “alternative” biochemistry would be one with differing chirality of its biomolecules. In known Earth-based life, amino acids are almost universally of the L form and sugars are of the D form. Molecules of opposite chirality have identical chemical properties to their mirrored forms, so life that used D amino acids and/or L sugars may be possible.


  4. island001 says:

    Great, I would recommend it, because this is all related intricately to the final theory of everything.

  5. invaderxan says:

    Interesting… Thanks for the links. I’ll look over them properly later, when I have the time…

  6. island001 says:

    What a surprise, I’ve been saying all of this for years:
    And then these guys figured it out:
    And after that, I realized how it applies to other life in the habitable zone:
    And there is a LOT more to it than anybody even realizes yet.
    I’d recommend this book:
    And these papers:
    Schneider, Eric D. and James J. Kay, 1994. “Life as a manifestation of the second law of thermodynamics.” Mathematical and Computer Modelling 19(6-8): 25-48.
    Schneider, E.D, Kay, J.J., 1994 “Complexity and Thermodynamics: Towards a New Ecology”, Futures 24 (6) pp.626-647, August 1994
    Schneider, E.D, Kay, J.J., 1995, “Order from Disorder: The Thermodynamics of Complexity in Biology”, in Michael P. Murphy, Luke A.J. O’Neill (ed), “What is Life: The Next Fifty Years. Reflections on the Future of Biology”, Cambridge University Press, pp. 161-172

  7. invaderxan says:

    Re: Non-biological amino acids
    Oh, that’s an interesting point — and one which eluded me totally!
    It would certainly be worth noting how the non-biological ones compare in terms of abundance. If any are comparable to the infamous 10, then it’s conceivable alien life might have incorporated those. Indeed, though my biochemical knowledge is pretty weak, I know that there are a number of “non-standard” amino acids even in terrestrial biochemistry.
    Logically, there’s no reason why any amino acids should be exluded from astrobiological searches given that, chemically, they all react in the same way (albeit with some energetic differences).
    Thought provoking. Thank you.

  8. Anonymous says:

    Non-biological amino acids
    This is an interesting paper. However, the researchers specifically excluded the “non-biological” amino acids that are found along with the 10 biological ones without providing much of an explanation of why they did so. Inclusion of these amino acids in their analysis would have been more interesting because the argument that they could never be included in the genetic code is not very clear, or is not clearly stated in the paper itself.

  9. invaderxan says:

    Oh, now that is interesting. Thanks. :)
    I’ve seen a few theories on D vs L enantiomers. One I rather like involves early proteins assembling via surface chemistry on diamonds and silicate crystals…

  10. Heh, rather interesting coincidence. I just came across this blog post that argues that there may be an intrinsic bias towards left-handed life.
    Of course, even given that, I don’t think it’s implausible that right-handed biospheres could exist. Although an early biosphere would, presumably, if that study’s conclusions are valid (for example, if that’s not simply a quirk of isovaline) have a preponderance of left-handed life, and that majority would give them an intrinsic advantage, if some early, crucial, advance happened to occur in a right-handed protocell rather than a left-handed one, right-handed life could gain the upper hand.

  11. invaderxan says:

    At least I won’t be the only unproductive one then! :P

  12. ryttu3k says:

    I get less done every winter AND get sick during it ;_; I swear, my marks / attendence rates / general mood are, like, a reverse bell curve.
    And heh. Since our winters are your summers, we can both be spaced out at the same time!

  13. invaderxan says:

    See, I’m totally the opposite. Cold keeps me alert and focussed. On the other hand, a couple of degrees too high and I start to lose concentration. Especially if it’s humid — I swear, I get less done in Summer!

  14. ryttu3k says:

    Oh, that’s not the problem, it’s basically everything I did last year, and that WAS fine XD It’s just that these lectures make me want to go to sleep!
    Also, the air conditioning in the lecture theatre is set WAY too high, even when it’s cold outside, and I suspect that I’m cold-blooded because my brain starts to shut down in cold weather ;_;

  15. invaderxan says:

    *sigh* And that’s the biggest problem in teaching. So many teachers don’t try and make it interesting. A boring lecturer could talk about the most exciting topic in the world and put students to sleep.
    Tell you what, let’s make a wager. I bet you that I can find something interesting about any concept that seems dull at first glance! What say? ;)

  16. invaderxan says:

    Good point!
    Thermodynamically, any two enantiomers are essentially identical. Chiral centres make little difference to enthalpic changes, at least in small molecules like these.
    Though I haven’t read much on the subject, no, there’s no obvious reason why life chose one chirality over the other…

  17. ryttu3k says:

    I have no doubt it does! My last chemistry teacher managed to make the way the periodic table is put together sound like epic poetry! It’s just got DULL this term since there’s no effort to make it interesting.

  18. invaderxan says:

    Surprisingly, it might do without you realising it! The thermodynamics here are actually pretty basic. Free energy change of formation (ΔGf) and similar.
    You just need to keep in mind — the examples your lecturer gives might not be very inspiring to you, but everything you’re learning has some really cool application! :)

  19. invaderxan says:

    You’re not the only one. Biochemistry always used to put me to sleep!

  20. The chirality issue is still applicable, though, right? That is, there’s probably no inherent preference one way or the other, so you could still end up with a planet with life that has a basis much like ours except with opposite chirality?

  21. ryttu3k says:

    …Ooh. That’s very cool. (If only Introductory Chemistry A had chemistry like this, I may actually do well in it!)

  22. That’s pretty interesting. I was always into astrobiology, but I didn’t like studying biochemistry :-P

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