John on December 1, 2009 at 9:39 am
Interesting but not entirely surprising report from Wired:
What may be the most thorough study ever of a single organism has produced a beta code for life’s essential subroutines, and shown that even the simplest creatures are more complex than scientists suspected.
The analysis combined information about gene regulation, protein production and cell structure in Mycoplasma pneumoniae, one of the simplest self-sustaining microbes.
In the new studies, German and Spanish researchers documented almost every single protein used by M. pneumoniae. They looked up the known functions of each of its genes, and made recordings of gene activity. They documented all the chemical reactions inside M. pneumoniae and mapped its physical structure. Then they put all this together.
What emerged was a picture of surprising complexity. M. pneumoniae needs just eight gene “switches” to control its molecular activities, compared to 50 in E. coli â€” a number so low that it implies other, as-yet-unknown regulatory processes. Groups of genes thought to work in unison did so only intermittently. At other times they worked in isolation, or in unexpected configurations.
M. Pneumoniae has around 800 thousand base pairs in its genome (compared to around 3 billion base pairs in a human cell). It is very, very primitive. And yet, as this story points out, even a primitive living cell requires a lot of complex nano-machinery. This presents a problem for just about any theory of spontaneous abiogenesis. In fact, it’s a real life chicken and egg problem.
In the rest of the history of life there is a simple response to all such problems, i.e. it evolved gradually over time. But you can’t have evolution without replicating life. And you can’t have replicating life (it appears) with much less than about 800K base pairs to code for all the operations necessary to sustain life. Life seems to require a quantum leap of information which has proven very difficult to explain.
Because DNA is an information bearing molecule, a sense of the raw data contained in the DNA can be expressed in more familiar forms. The conversion is complicated (and frankly math was never my strong suit) but a rough estimate is 2 bits of data per base pair. In this case that would work out to 1.6 million bits for the M. pneumoniae genome or, dividing by eight, around 200,000 bytes. So very roughly we’re talking about 200 kilobytes of data, a fifth of a megabyte. In the case of a primitive organism with few if any redundant genes or processes, even a handful of bits out of place will likely result in death. So how do we get from non-living chemistry to a living cell when the leap is 200 kb of precisely ordered data?
In the 50 years since the discovery of the structure of DNA, surprisingly little progress has been made on this problem. Perhaps it is solvable and I would never suggest science stop looking for a solution, but at present no obvious solution or avenue to a solution presents itself. While I’m not overly-fond of God-of-the-gaps arguments, there are a few cases (and this is one) where the gaps seem fairly stubborn. Indeed, the more we know about minimum complexity, as the Wired report suggests, the bigger the gap seems to get.
Category: Science & Tech |