I'm sure many of you have heard about the bacteria that was found to substitute arsenic instead of phosphorus into its macromolecules. It is a very interesting discovery--the first we have discovered of an organism capable of not only withstanding arsenic but using it in its molecules. There's still a lot that remains to be discovered, but it's a good first step. Be leery of what you read in the media, though. The writers of the paper, in typical scientific fashion, are not particularly explicit in what the "evolutionary and geochemical significance" is. What do you think?
Be leery of what you read in the media, though. The writers of the paper, in typical scientific fashion, are not particularly explicit in what the "evolutionary and geochemical significance" is. What do you think?
How is that typical and why should we be leery because of it? The significances is that it expands on the basics of what life can be made up of, thus expanding on where life can exist. Though these bacteria aren't really anything new we've known about bacteria that can use arsenic for decades.
The significance of it is that before, we were limited to thinking of life on other planets in terms of our own biochemistry and DNA structure - but this discovery shows that much more is possible than what we thought before - and that substitutions in DNA are more easy/possible than we thought. It basically means that life can adapt and evolve in a much different way than we thought it could - meaning that life could exist in many places we once thought impossible. It lends new possibility to life in the methane lakes of Titan, for example.
Phosphorus is present in nucleotides and nucleic acids - which all organisms contain and which carry out very important functions.
ATP - Adenosine Triphosphate contains 3 phosphate groups. Each phosphate group has a negative charge, causing this molecule to be unstable. The thermodynamics are such so that the phosphate group can be transferred and release just enough energy for many processes to occur. This molecule fuels the cell. This molecule would have to become Adenosine Triarsenate with this arsenic. This does not make sense because the arsenate groups would undoubtedly be different from the phosphate groups and the thermodynamics would be messed up, causing the organism to be dysfunctional.
Phosphate groups are also essential for DNA replication and protein synthesis. They are a component in our DNA.
I am not saying that an arsenic-based bacterium does not exist. However, it seems highly unlikely that such an organism evolved a mechanism to substitute arsenic in the DNA and many biomolecules and survived.
Einfach's skepticism are the perfect example of why this is so important, we used to think phosphorus was needed, but it turns out it isn't in all cases. Thus, life can come from a lot more than we thought it could before. there's most likely some other difference in its DNa that hasn't been discovered/mentioned in the media yet - we'll have to wait and see.
Einfach: You are absolutely right about what happens with arsenic. In fact, that's why it's a toxin. If you know about periodic trends, arsenic is just a period under phosphorus, meaning that it has very similar chemical properties, but not similar enough. The body tries to use the arsenic as phosphorus and fails. Somehow, these organisms have managed to adapt into a highly toxic environment.
Note, however, that they still must retain some phosphorus to survive. As it turns out, phosphorus is still needed in some quantity; we have not managed to completely starve the bacteria of phosphorus.
How is that typical and why should we be leery because of it? The significances is that it expands on the basics of what life can be made up of, thus expanding on where life can exist. Though these bacteria aren't really anything new we've known about bacteria that can use arsenic for decades.
The bacteria are new in that they actually incorporate the arsenic into their macromolecules, not just fiddle around with the electrons on the arsenic (oxidation/reduction). So that's why this discovery is considered a new one. Substitution of different molecules is nothing new, though. For example, copper is a substitute for iron in oxygen-carrying molecules for many organisms.
As for being leery, I meant towards media treatment of the subject, which is well-meaning yet misguided at times without reference to the source material. You've found yourself a good source though that explains the experiment very clearly and correctly, so that would be fine.
Each DNA nucleotide has a phosphorus group attached to it, with forms a hydrogen bond with a hydroxide group of an adjacent nucleotide to create a single strand of DNA... RNA is similar, with the phosphorus-OH bonding... These bacteria must use an arsenate group instead...
Phosphorus and Arsenic are in the same group on the periodic table, meaning that they have very similar chemical properties... Due to having the same number of valence electrons...
Personally, I think this is very exciting. As said above, it opens the possibility for MORE life on alien planets. The goldilocks zone just got a lot larger...
@Psychoace - This is true, but phosphorus is unique in its thermodynamic properties. Nitrogen is also in the same column, but you cannot simply substitute Nitrogen for all the phosphorus in your body or vice versa (Combining Nitrogen with Oxygens forms chemicals like Nitric Oxide, Dioxide, etc. whereas a phosphate group is Phosphorus bonded with Oxygens on all sides. Nitric Acid is HNO3). Surely these molecules / molecular groups have very different properties.
While the thermodynamic properties do apparently make it severely unstable it is also hypothesized that pre-bitotic arsenic is not solely arsenic. Arsenic is slightly larger then phosphorus and the bond length is 10% greater. This instability and diminished half-life of the DNA molecule and other arsenic based compounds is the primary conjecture of this theory. While some of the key properties of phosphate such as its thermodynamic instability as well as its kinetic stability make it advantageous for Earth's biological life, arsenic may be more thermodynamically realistic for life on other planets or moons such as Saturn's moon Titan.
Anyway it wasn't something that just happened. Scientists did it themselves.
It was probably stated in that clip that Mage has, but some scientists are discrediting NASA because there were apparently "flaws" in the experimentation with the bacteria. (I read all of this here). First, they say that they are unsure if the bacteria actually used the arsenic or if the arsenic was just staying inside the bacteria. They also said that based on the NASA scientists lab journal, it appears that the bacteria were fed salt with trace amounts of potassium. So maybe NASA didn't find anything special.
*is satisfied that this is not a concrete discovery*
If their wish does come true, it would be a rather exciting discovery. Arsenic is a rather deadly poison to virtually everything, and the discovery of a bacteria that relies rather heavily on it is a good find. I wouldn't blow it up right now, even if it were concrete. We still would have no idea what this entail. All theories and predictions are just that: Theories and predictions.
Oh, and got to love how Faux news was reporting it as extraterrestrial life.
Offtopic: I have to call you on this. I understand it's futile to tell you that Fox isn't biased (they are, after all), don't take a statement that they made quoting another source (NASA) as their thoughts. That is all.
Eh, I don't recall NASA citing it as extraterrestrial life in the story I read. I do recall that they said that it was going to change what we look for in our search for extraterrestrial life, but not that it was extraterrestrial. Here's the NASA page which contains their story.
Offtopic: I have to call you on this. I understand it's futile to tell you that Fox isn't biased (they are, after all), don't take a statement that they made quoting another source (NASA) as their thoughts. That is all.
As Walker pointed out they didn't make such a claim. So it was just Fox talking out of there back sides again.
