Unlocking the Mystery of Life

Imagine storing books in DNA and sending them across a biological Internet. It’s already happening.

The media has been buzzing about NASA’s claim that scientists that have discovered “life as we do not know it” (MSNBC)–purportedly finding bacteria that can use arsenic instead of phosphorous in its DNA. David Klinghoffer already blogged about this story here, interviewing astronomer Guillermo Gonzalez (who has conducted research on astrobiology) on the find. The public first became aware of this story last week when NASA announced it would be holding a press conference that would reveal “an astrobiology finding that will impact the search for evidence of extraterrestrial life.” NASA’s announcement inspired a chorus of speculative excitement among materialists and UFO true-believers alike, who stated things like: NASA is holding a press conference on Thursday to make an announcement. Read More ›

Every once in a while an article comes out on a new DNA repair mechanism or a new feature of a known DNA repair mechanism. There are so many complexities behind DNA repair and there is still more to uncover. Last October, a review article came out in Molecular Cell on regulatory factors for DNA repair mechanisms (Molecular Cell 40(2), October 22, 2010, 179-204). Basically, DNA repair mechanisms are very powerful because they can often replace or remove nucleotide bases. So these powerful mechanisms need something to make sure they do their job properly and not destroy the whole genome in the process. That is where regulators come in. If DNA repair mechanisms are medics flying out to the damaged site, then the regulators would be the control tower that finds the sites, guides the planes, and tells them when to get to work and when to retreat.

The question of the evolution of eukaryotic cells from prokaryotic ones has long been a topic of heated discussion in the scientific literature. It is generally thought that eukaryotes arose by some prokaryotic cells being engulfed and assimilated by other prokaryotic cells. Called endosymbiotic theory, there is some empirical basis for this. For example, mitochondria contain a single circular genome, carry out transcription and translation within its compartment, use bacteria-like enzymes/components, and replicate independently of host cell division and in a manner akin to bacterial binary fission.

Despite such evidence, however, when assessing the causal sufficiency of unguided processes, they — predictably — come up short. After all, it is all-too-easy to lapse into a long-discredited Lamarckian “inheritance-of-acquired-characteristics” mentality. It is important to bear in mind that, even if a cooperative assemblage of prokaryotes did by some fluke of luck arise, such an arrangement is of no evolutionary significance unless there is a genetic basis to ensure its propagation.

A second problem with this scenario is that mitochondria use a slight variation on the conventional genetic code (for example, the codon UGA is a stop codon in the conventional code, but encodes for Tryptophan in mitochondria). This implicates that the genes of the ingested prokaryotes would need to have been recoded on their way to the nucleus. The situation becomes even worse when one considers that, in eukaryotic cells, a mitochondrial protein is coded with an extra length of polypeptide which acts as a “tag” to ensure that the relevant protein is recognised as being mitochondrial and dispatched accordingly. The significant number of specific co-ordinated modifications which would be required to facilitate such a transition, therefore, arguably make it exhibitive of irreducible complexity.