7
$\begingroup$

What sort of xenobiochemistry would support information-carrying macromolecules like DNA if only trace amounts of phosphorus were present on an alien planet? Since the phosphoribosyl backbone of DNA would not be possible in such an environment, what might be a viable substitute?

$\endgroup$
2
  • $\begingroup$ The answer to the question as asked is obviously arsenic, which is the closest to phosphorus in terms of chemical behavior. However, the question is nonsensical. In a world where phosphorus was exceedingly rare, biochemistry would have no reason to develop along the same paths as on Earth, where phosphorus is merely scarce. So, the energy carrying molecule would not be a homologue of ATP. $\endgroup$
    – AlexP
    Sep 1, 2018 at 11:45
  • $\begingroup$ You might want to take a look at this: biology.stackexchange.com/questions/11286/… $\endgroup$
    – John Locke
    Sep 1, 2018 at 13:27

3 Answers 3

8
$\begingroup$

There is a rather controversial example of bacteria here on earth that used Arsenic instead of Phosphorus

http://en.wikipedia.org/wiki/GFAJ-1

Subsequent studies refuted the claim, but it's a starting point. It's plausible that a DNA like molecule could form with Arsenic instead of Phosphorus as Arsenic is directly under Phosphorus on the periodic table. This means it has the same number of valence electons, which is important in molecular bonding, and similar physical properties.

Arsenic is a semi-metal, you could probably use Nitrogen in the same way as both Phosphorous and Nitrogen are non-metals.

$\endgroup$
6
  • $\begingroup$ I've discounted N, but probably shouldn't. Nitrate doesn't seem to behave like phosphate. I'd have to look into why, and whether my gut feeling is accurate. The candidate has to do two things: 1) permit conformations necessary to stabilize a double helix (assuming like DNA), and 2) release free energy necessary to polymerize the building blocks. dATP + DNA(n) -> PPi + DNA(n+1) -> 2 Pi + DNA(n+1). The last step is important because it makes the reverse reaction almost impossible. Of course, the temperature and other factors could profoundly affect behavior. $\endgroup$ Nov 6, 2014 at 20:26
  • $\begingroup$ TBH, that's getting past my understanding of organic chem. $\endgroup$
    – user772
    Nov 6, 2014 at 20:53
  • 1
    $\begingroup$ OK, found a ref for N being limited: chemed.chem.purdue.edu/genchem/topicreview/bp/ch10/…. The reason is it doesn't have any d orbitals, so the bonding complexity is reduced. $\endgroup$ Nov 6, 2014 at 21:03
  • $\begingroup$ How about Arsenate? en.wikipedia.org/wiki/Arsenate#Arsenate_poisoning It appears arsenate and phosphate are relatively interchangeable. Also depends how real you want to get, if the world requires a high level understanding of chemistry to notice a potential flaw, it's probably good enough for everyone else. $\endgroup$
    – user772
    Nov 6, 2014 at 21:08
  • 1
    $\begingroup$ Here is a reference containing one answer to the arsenic loving bacterium. normalesup.org/~adanchin/origine/arsenic.html The author claims arsenic is removed by making insoluble As-S compounds, and scavenging traces of P. $\endgroup$ Nov 6, 2014 at 21:28
2
$\begingroup$

Arsenic, bismuth and antimony should be able to replace phosphorus because they're all in the same group. I haven't tested the chemistry with these yet, though.

$\endgroup$
0
$\begingroup$

Life doesn't need phosphorus. Life that evolved on Earth mostly needs phosphorus though some bacteria use arsenic instead. A genome programmed in peptide nucleic acid does not use phosphorous. A goethite protein matrix bones and teeth don't need phosphorus. That's basically limpet teeth. Look it up if your interested. I find them fascinating. Adenosine triphosphate does need phosphorus, but ATP is not needed in life. It's just an energy carrier because a single oxidized glucose molecule produces far more energy then cells typically need at any given point. ATP is just little bite sized bits of energy. If the cell has a capacitive membrane then glucose can be oxidized directly, all the energy stored, and conducted out in appropriate amounts as needed. For instance, different proteins have different geometries and electrical properties. Electrostatic charge will alter the way the proteins fold depending on the proteins specific geometry and resistance. Proteins touching the part of the membrane that discharges takes exactly the energy needed, with just some minor losses to do it's folding thing.

Ta-da! Metabolism without phosphorus. That's the gist of what atp does. It's able to rapidly charge and discharge with very tiny amounts of energy, but that isn't actually needed. So long as cells can harvest and transform energy from food sunlight or whatever and use that energy to move and read/write it's genetic code for self replication it will work and phosphorus is not needed. Will something evolve to not need phosphorus? Given how rare phosphorus is cosmically I'd say it's likely, but I don't know. I do know it can be artificially made.

Hope this helps.

$\endgroup$
2
  • $\begingroup$ That the GFAJ-1 organism would use arsen instead of phosphor is largly seen as discredited - see en.wikipedia.org/wiki/GFAJ-1#Criticism $\endgroup$
    – Trish
    Aug 15, 2023 at 18:49
  • $\begingroup$ News to me. Thanks for the link. Most of my post is about avoiding an energy currency stepping stone so it still works even if that bacteria is a poser. $\endgroup$ Aug 15, 2023 at 19:37

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .