Arsenic life – more criticism, formally published

By Grant Jacobs 29/05/2011

Science magazine has lined up eight Technical Comments on-line in advance-of-print release, along with a response to these from the authors, that will stand alongside ’the’ arsenic life paper to be published in in print next week’s edition after a wait of roughly six months. With the exception of the accompanying editorial, these are all open-access.

For those new to the story, the ‘lite’ gloss–i.e., for a non-scientist readership–of this research arguing that a bacteria uses arsenic in place of phosphate in it’s DNAgoes something like this.

DNA is made of a phosphate-dioxyribose backbone and nucleoside bases. The backbone is the same for each repeated unit in DNA (a nucleotide), a phosphate group linked to two sugar molecules (ribose sugars), one linking to the base before the phosphate and one linking the base after it. There are four different bases[1] – these make up the ‘code’ that various along the length of the DNA molecule.

An atom with some similar properties to phosphorus is arsenic (strictly speaking the comparison should be of phosphate and arsenate, but let’s it stand). You can see this by viewing the periodic table: arsenic (As, 33) is immediately below phosphorus (P, 15) – atoms with similar properties lie in the same or nearby columns in the periodic table.

While phosphorus is one of a small number of elements considered essential for life, arsenic is generally consider toxic.[2]

Felisa Wolfe-Simon and colleagues have argued that a bacteria[3] isolated from California’s Lake Mono has arsenic in place of phosphorus in (some of) it’s DNA.

This was announced by NASA, teasing the announcement before the release of the paper as being relevant to life outside earth. (The connection being that, in principle, life might have a different chemical basis outside earth.)

This research paper, an on-line in-advance publication in Science, immediately provoked a response from scientists on-line, both in blogs and on twitter, e.g. under the #arseniclife hashtag. Long story short, a number of strong difficulties to this being correct were pointed out.

Many of these early objections have now been captured in the Technical Comments presented on-line in advance for print publication next week. Prof. Rosie Redford has summarised these on her blog. A number of summaries of the full story have been written. While I quibble at various details, but rather than repeat what others have written, you can decide for yourself from these (among many others):

Dive in. There’s plenty to chew on.


[1] Actually, there are modified bases as well. Examples include the methylated and ethylated based that have a role in epigenetics.

[2] Other elements are used, but in small quantities.

[3] Named GFAJ-1: Get Felisa A Job. (Seriously.)

Other articles on Code for life:

NASA: science shouldn’t be debated in media and blogs?!

Autism — looking for parent-of-origin effects

New academic visas for New Zealand

Finding platypus venom

Choosing an algorithm — benchmarking bioinformatics

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