Simple Cells?

This item was originally posted in March, 2006. It is now part of my blog recycling program. Because I have more people reading The GeoChristian now than I did a year ago, I will occasionally go back and re-use some of my best blog entries.

Having read a number of technical books and papers on the topic of the origin of life, I believe that there is more here than a “god of the gap” kind of argument. Experiments have shown that conditions may have been present on the early Earth for the formation of a few basic building blocks for life in the primeval oceans, such as amino acids. But the complexity required for a metabolizing, reproducing cell to develop is an enormous leap beyond this. We can argue against the naturalistic origin of life not because of our ignorance–this is the idea of invoking the “god of the gaps”–but because of our knowledge of just how improbable this occurrence would be.

Prominently displayed in the back of my science classroom at Bucharest Christian Academy is an oversized poster showing biochemical pathwaysthe enzyme-mediated processes that occur in all cells, in organisms ranging from bacteria to humans. The poster presents an incredible amount of information, outlining processes such as electron transport in the mitochondria (in eukaryotes), and the synthesis and degradation of amino acids, carbohydrates, lipids, and nucleotides. The poster is a little overwhelming to my middle school and high school students, but that is part of my purpose for having it. Even the most simple living cells are incredible machines, and I want them to have a glimpse of what that means.

For the web site of the week, I have chosen a similar metabolic pathways poster from the ExPASy Proteomics Server. By clicking on individual tiles on the poster, you can zoom in to see details of various processes, with the names of the enzymes that control molecular transformations in blue.


From discussions with biochemists, my understanding is that the simplest cell that could perform the basic functions of life (such as respiration, digestion, reproductionprocesses that define life) could do without some of the processes diagrammed on this poster. However, this primitive cell would still have to include about 60% of the processes depicted on these types of posters. This defines the magnitude of what needs to be explained in any naturalistic explanation for the origin of life.

Grace and Peace

I did find one article (I’m sure there are many) on the internet that puts a lower limit on the number of proteins in the most primitive cell at 300. Note that on the metabolic processes poster I have here, only the blue names, the enzymes, are proteins. The other substances are all substances that are produced or modified by those enzymes.

My biochemist friend Glenn added this comment when I posted this last year:

There’s an additional complexity issue that’s not reflected in the 2D network map of biochemical pathways: the 3D structure of the cell is critical for enzyme function and the transport of substrates/products. Many of these enzymes are membrane-associated, for example, and their orientation in the membrane defines their overall function. Experimental data suggests that very few enzymes are “floating” around in a cellular soup; it’s a viscous, structured arrangement. So you could put all the enzymes on the chart into a tiny test tube, and add all the substrates in solution, but it wouldn’t operate as a cell does. Yes, enzymatic reactions would occur. But it’s not a sustaining cellular system.

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