Metabolism: A Cascade of Design

Metabolism: A Cascade of Design

Charles Darwin’s view of the cell differed greatly from the picture we have today. Darwin held to the protoplasmic theory— the idea that the cell consists only of a wall surrounding a nucleus and a homogeneous, jelly-like protoplasm. Biologists at the time could readily envision chemical routes that could produce the single ingredient believed to form this jelly, making evolutionary explanations for life’s origin plausible.

By the end of the 19th century with the rise of biochemistry, however, the protoplasmic view of the cell waned. Scientists clearly recognized that the protoplasm was a complex, heterogeneous system. But it’s not merely that the cell’s biochemical systems are complex; new research attests that they also appear to be optimally designed.1

Many proteins take part in the metabolic processes in the cell’s protoplasm. Metabolism refers to the myriad, life-essential chemical reactions that occur in organisms. Metabolic activity makes it possible for organisms to extract energy from the environment and make life’s component parts. These processes allow organisms to grow, reproduce, maintain biological structures, and respond to changes in the environment.

Metabolic processes within the cell’s interior are organized into pathways consisting of a series of chemical reactions that transform a starting compound into a final product via a series of small, stepwise chemical changes. Each step in a metabolic route is mediated by a protein (called an enzyme) that assists in the chemical transformation.

Metabolic pathways can be linear, branched, or circular. The chemical components that are part of a particular metabolic sequence sometimes take part in other metabolic pathways. These shared compounds cause metabolic pathways to be networked together.

Like all networks, metabolic pathways are susceptible to failure cascades. These breakdowns result from defects in the enzymes that catalyze the individual steps of the pathway. Because the pathways are reticulated (interconnected), an error resulting from the failure of even a single enzyme will cascade through the network. This problem is similar to the widespread power outages that occur when a single line of a power transmission network becomes overloaded.

A team of biological and chemical engineers wanted to understand just how robust metabolic pathways are. To gain this insight, the researchers compared how far the errors cascade in pathways found in a variety of single-celled organisms with errors in randomly generated metabolic pathways. They learned that when defects occur in the cell’s metabolic pathways, they cascade much shorter distances than when errors occur in random metabolic routes. Thus, it appears that metabolic pathways in nature are highly optimized and unusually robust, demonstrating that metabolic networks in the protoplasm are not haphazardly arranged but highly organized.

This organization evinces the work of a Creator. The researchers note that “In man-made systems, this balance [robustness] may be the culmination of human intervention.” 2 If so for human networks, then is it reasonable to think that nature’s networks reflect the product of undirected evolutionary mechanisms, or of creation? I wonder what Darwin would have thought?

  1. Ashley G. Smart, Luis A. N. Amaral, and Julio M. Ottino, “Cascading Failure and Robustness in Metabolic Networks,” Proceedings of the National Academy of Sciences, USA 105 (2008): 13223–28.
  2. Ibid.