New Research Reveals Insight into Life’s Minimum Complexity
First impressions mean a lot. My initial exposure to introductory undergraduate classes in biochemistry, molecular biology, and cell biology got me excited about the prospects of becoming a professional biochemist. Once in graduate school, I had the opportunity to take advanced courses in biochemistry and biophysics; I began routinely reading the scientific literature and started conducting my own original research.
These learning experiences helped me apprehend the detailed inner workings of life’s chemical systems and, with it, allowed me to genuinely appreciate first-hand the complexity of biochemical systems. But it wasn’t just the complexity that impressed me, their elegance and sophistication also stuck out. It seemed to me that a mind must be responsible for putting life together at its most basic and fundamental level. This intuition sent me on a journey that culminated in my conversion to the Christian faith.
Biochemical systems appear to be so intricate and complicated that it’s difficult to envision how undirected chemical evolutionary processes could have generated them. But is there any way to rigorously determine these systems’ complexity? In the last decade or so, life scientists have developed a number of methods that now allow us to better assess, both qualitatively and quantitatively, the minimal biochemical complexity of living entities.
As discussed in my books Origins of Life and The Cell’s Design, researchers have both experimentally and theoretically estimated that an organism’s genome must contain a minimum of about 400 genes (this is called the essential gene set) to even be recognized as living. Other studies indicate that some of these essential genes’ protein products must be spatially and temporally localized within the cell for life to be possible, indicating that even in its most minimal form, living systems require organization. (Go here, here, and here for brief descriptions of recent work on life’s minimal complexity.)
Results from more and more studies are indicating that the organization of complex biochemical systems is far more extensive than anyone realized. And these implications raise troubling questions for evolutionary explanations for life’s origin. In this article I want to focus on a recent review article published in Science by Lucy Shapiro and Richard Losick, two microbiologists who have spent much of the last two decades performing research that has fundamentally altered the way we view bacteria (the simplest life-forms on Earth) and the minimal complexity of life.
In graduate school, I did a fair amount of work on the outer membranes of the gram negative bacterium Salmonella typhimurium and, in the process, learned a lot about the biochemistry of bacteria. At that time (the mid 1980s) life scientists regarded bacterial cells as highly disordered systems. According to Shapiro and Losick, “Bacteria were once viewed as amorphous reaction vessels with chromosomes that wandered freely and randomly throughout the cell.” But, as they point out, new measurement technologies have “revealed a strikingly complex inner world within bacteria. This inner environment is exquisitely organized.” This organization stems in part from the localization of proteins within the cell’s interior.
The review article provides an overview of recent work on protein localization in bacteria, noting that the emphasis is shifting from identifying which proteins are localized to trying to understand why and how localization occurs. Researchers haven’t made much progress in figuring out why individual proteins localize in the cell, but based on a few glimmers of insight, they are convinced that this localization is critical.
On the other hand, investigators are beginning to learn quite a bit about how proteins become localized in the cell. It turns out the localization mechanisms are diverse and elaborate. One of the most prominent mechanisms, known as diffusion and capture, involves a localized protein complex that serves as a target. The protein slated for localization within that complex is captured as it diffuses throughout the cell and, thus, encounters the target. Researchers recognize that this can’t be the ultimate explanation for localization because it doesn’t adequately account for how the target protein complex itself first becomes localized.
But recent studies have identified several of these cues, such as the curvature of the cell membranes. Some proteins readily bind to the surfaces of membranes with positive curvature and others to membranes with negative curvature. Once these proteins bind, they are able to form complexes that can then capture other proteins as they diffuse throughout the cell.
Prior cues for localization also arise from the mother cell. Proteins localized in a bacterial cell will remain localized as that cell undergoes division to generate two daughter cells. This carry-over process sets up a never ending series of cues from generation-to-generation with target complexes being inherited instead of forming from scratch in each daughter cell.
There is still much to learn about why and how protein localization takes place. But one thing is clear: localization appears to be a defining feature of bacteria. Life is minimally complex, but it is also organized at its most basic level, which creates problems for the evolutionary paradigm. Internal organization has to be accounted for in all origin-of-life models. The localization of proteins adds another dimension to life’s minimal complexity. In other words, origin-of-life researchers must not only account for the simultaneous occurrence of a relatively large number of gene products, but also for their spatial and temporal organization.
Common experience teaches that it takes thought and intentional effort to carefully sort out a space for functional use. Instead of being a jumbled mess, the interior of the simplest cell is best described as a factory that has been carefully prearranged to efficiently carry out life’s most basic processes. For this reason, the surprising internal organization of bacterial cells points to the work of a Mind.