New Thinking About the Origin of Life (2): Catalysts and Containers

Jeremy Sherman’s book, Neither Ghost Nor Machine: The Emergence and Nature of Selves, describes Terrence Deacon’s theory of how, from lifeless chemical reactions, self-generating arrangements of molecules might have emerged that led to the first living cells. In the previous post I summarized highlights of Sherman’s description of purpose and self-ness as the distinguishing features of not just humans but of all living things. All living cells—as selves—share three abilities: self-repair, self-protection, and self-reproduction. Ordinary chemical reactions lack all three and soon fizzle out, their components lapsing into the disorder that overtakes any reaction that cannot sustain itself long enough. What kinds of reactions could come together to meet that requirement?

Catalysts are part of the story—perhaps even the heroes. Catalysts are substances that speed up a chemical reaction without themselves being altered. Sherman compares catalysts to a wheelbarrow used “for hauling gravel over a hill. Without the wheelbarrow, it takes a lot of work to move the gravel. With it, the gravel moves more efficiently and the wheelbarrow isn’t altered in the process. Its presence therefore reduces work, haul after haul” (140).

An example of catalysts that we put to use most days is the catalytic converter built in to the exhaust pipes of our cars. The converter consists of metal plates coated with a catalyst such as aluminum oxide that converts the engine’s polluting exhaust that flows over the catalyst into carbon dioxide and water that comes out the tailpipe. The catalyst itself is never used up.

Now imagine this: chemicals A and B, helped along by catalyst X, react to form a compound. Catalyst X itself is not used up; it continues to speed the reaction as long as sufficient A and B are around. Now assume that the compound produced by this reaction is X itself, the same chemical, Catalyst X, that boosted the reaction. The result? The total amount of X—the original amount that never diminishes plus the added amount produced by the reaction—increases rapidly. This is autocatalysis (stress on tal), a sequence, a chain of reactions, in which a chemical reaction happens to produce the catalyst that stimulates the reaction itself. Autocatalysis takes many forms, with different reactions producing various compounds and catalysts, sometimes in a sequence but always coming full circle to add to the existing supply of catalyst.

Now “Imagine,” Sherman writes, “autocatalysis occurring within a container. It would look a little like a very simple cell—a chemical population explosion occurring within something like a cell membrane….Imagine that one of the autocatalytic by-products was a capsid molecule [a protein that forms a shell, usually around a virus],… yielding a container” (152). Deacon calls these proto-cells autogens—self-generators.

Still, container or not, even autocatalysis winds down when it runs out of fuel. The key to Deacon’s theory is that another reaction takes place to constrain the autocatalysis and resupply it. Moreover, this second reaction would also fail at some point were it not also constrained in turn by the renewed catalytic cycle. The second law of thermodynamics wins if a reaction or the structure of something is left to itself; things come apart, break down, disperse. But if two reactions are such that they stop each other and resupply each other before one fizzles out, the second law must come back another day.

The formation of the container is the second reaction here and the container will sooner or later break apart, perhaps after a large molecule bumps into it. When that happens, the capsid molecules that form the container will drift away, the catalysts inside the capsule will come in contact with new reactant molecules in the environment, the reactions will produce more capsid molecules which will in turn form containers around new clusters of reactants and catalysts. In this way, at this stage in their cycle, the autogen as a whole has repaired and renewed itself. The cycle seems complicated, but the following video illustrates it well.

Terrence Deacon, Origins of life, Autogen Demonstration – YouTube

A five-minute animated video about Deacon’s autogens (“autocells” in the video).

 

 

 

 

 

This cycle of closed container-open container-closed container sound far-fetched until we realize that it’s a pattern that echoes through the living world. Sherman points out that the cycle parallels that of a plant’s protected seed that opens to release an array of molecules that regenerate and arrange themselves again into plants that produce new seeds. “In a very loose parallel, a sunflower isn’t the seed phase or the plant phase but the complementary tendency to alternate between the phases. The autogen is even a little like the chicken and egg. Regardless of which comes first, we identify the pair of alternating phases as a self within a lineage of selves” (165).

Among non-living things, fires burn out, even rocks erode. But autogens are able to postpone the disorder and the dispersal that characterizes lifeless matter by building phases of reshuffling and rearrangement into their cycle. And autogens evolve, as certain varieties come to outnumber others. Some capsules become more likely to open in the presence than in the absence of  fresh reactants, improving their efficiency. Others carry around a template, an early kind of DNA, that preserves a particular sequence of, for example, a successful catalytic reaction. In such ways, “selves resist nonexistence” (193). And while autogens are not living cells, with each change that makes them better at persisting, they get closer.