Of ET, Astrobiology and Arsenic

Posted December 3rd, 2010 by admin

Pandemonium broke out that NASA had found alien life – this then slowly turned into new type of life on Earth. Being in love with extremophiles and loving the concept of alternative life chemistries I found myself scratching around for more information.

The reports I was seeing was saying the microbial life form was interesting because it used Arsenic – but I know that there are quite a few things that metabolised Arsenic or at least have a tolerance to it.

I finally found things that said that the organism was made of Arsenic – this made more sense. That it was subtsituting Arsenic for Phosphorus – at first I thought “well duh it just has a tolerance to arsenic”. Arsenic is toxic to us because it gets into our major biological molecules.

If the organism is made of Arsenic as in it’s DNA etc… though rather than just the odd substitution here and there it becomes more exciting. Phosphorus is fundamental in making up the sugar backbone of DNA, it is part of every major bio molecule. DNA, RNA, proteins so that is our genetics and our enzymes for a start. Then there are the ‘powerhouses’ of cells in which energy is stored in bonds broken and formed between ATP and ADP – the P stands for Phosphorus!

And then there is the membrane of the cells themselves – they are made from phospholipids, this are fatty chains and Phosphorus again.

Before I go on about what this means – I watched the NASA press conference on it all yesterday. And the organism is a microbe from Mono Lake in California – this is a harsh environment full of heavy metal salts and the like. It is toxic and should be as dead as a door nail but it is teeming with life. Extremophiles are extremely interesting when you are thinking about possible habitats for life and therefore where to actually look for ET. But more over it looks like life on earth evolved from extremophiles and that on the early earth they may have been the norm – this would make most of the things we think of as ‘normal’ including ourselves the outliers and so the actual extremophiles!

I have to say before I continue that I found the press conference highly frustrating – it was obviously for the general public so didn’t even touch on a lot of my questions and the girl who made the discovery was rehashing and labouring the same points over and over (which is needed). Then a few of the other expert panel had a tendency to use long words that were not part of the science but just long words which I felt destroyed the whole “general public” feel of the thing.

Anyway – the organism is not made of Arsenic as such but it would appear that it can substitute Arsernic for Phosphorus without it being toxic – in fact put in conditions were it had everything it needed to grow except Phosphorus in a solution laced with Arsenic it still grew!

When they looked closely it appears that there is at least a band of DNA that is taking up the As and using it as P. Now from what I understood the organism is still mainly the same as the rest of us terrestrial organisms but can replace the use of P for As in it’s major biological molecules – only some of the DNA has been confirmed.

Now according to Steven Benner – Arsenic is easy to sub into DNA hence being toxic to us because it actually goes in easier than the P but it forms a shoddy link in the molecule – it is almost the same as P being just below it in the periodic table but those slight differences mean that it is not an exact fit. For most organisms this means that it can cause the DNA to break down at the points where the Arsenic is (or at least that is what I understood!).

Thinking about this I would think that the difference in electron orbitals (which is the main difference as the size (not mass) of the atoms nuclei is almost the same) would mean that the distribution of charges that allow weak linking and complex molecular shapes such as proteins have etc… will be different. This may mean that the bio molecules will not want to retain the same shapes and would need to be forced into shape by something else in the cell in order to stop a chain reaction resulting in the biochemistry no longer working. Biochemistry is lots of loops and chains interconnected with both positive and negative feedback loops in it – in other words it is a complex and delicate system. There are plenty of buffers there and even in ‘normal’ biochemistry it has been found that things like prions are needed to force errant proteins into shape so that all the reactions can occur in the right places, at the correct speeds, when they are needed.

This organism – is metabolically ‘normal’; it’s just doing what the rest of us are doing! It is not ET but it is interesting. A lot of what was being said yesterday was that it completely changes our perspective on things – I however have always gotten myself into debate about this subject because I quiet frankly have come across to many things that break Occam’s Razor and the whole concept of only looking for Earthlike extraterrestrial habitats because it’s easy but saying it’s because that is what life is likely to look like!

I will endeavour to write more on these subjects but for those who want to know more I suggest you head over to the NASA website.

One of the main confusions I have seen arising is that people think the organism is special because it can eat/metabolise Arsenic – this is not the case – there have been several discoveries of such organisms – it is special because it is using Arsenic as part of it’s structure!

It is also scientifically exciting because it shows that biochemistry is the process and not the components – something I used to get myself in trouble with during my Undergrad studies.

One Response to “Of ET, Astrobiology and Arsenic”

  1. Snell-Pym » Astrobiology Blues

    […] no they couldn’t have my laptop and then spent this morning writing about it on my rarely updated Astronomy blog. This made me feel better – but I still haven’t got the paper to read :/ And I’m not even sure why […]

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