cell membrane http://people.csail.mit.edu/jaffer/GTOL/membrane

Membranes and Cell Division

At the outset, I expected membranes to be a crucial component of early evolution. The games were to include rules relating to topological properties of membrane enclosed regions.

But as the Nucleotide Game played and evolved, the need for introducing membranes never arose. It appears that membranes are not necessary for the emergence of life, defined here as the appearance of Universal Constructors, self replicating machines with the computational power of a Turing machine.

This does not mean that membranes might not be necessary for more advanced life forms; just that membranes are unnecessary for evolution to the point of translation of genetic information into non-genetic molecules.

In hindsight, this should have been obvious because ribosomes can operate in the absence of membranes, while most other cellular processes and organelles are critically dependent upon them. This leads to the question:

During the emergence of viroids, membranes are merely obstacles. Viroids trapped in vacuoles would replicate slowly if at all because they would consume all the free nucleotide monomers in their vacuoles. But vacuoles would provide some safety. In order to gain both benefits, viroids would evolve so that they could pierce and penetrate vacuole membranes.

As the Nucleotide Game evolves, it may well select for piercing molecules to be attached to the chromosome or its capsid. Viruses must also be able to escape their enclosures. Because capsids will evolve even in the absence of membranes, it is reasonable to expect that viruses which reside in vacuoles will escape as part of their life cycles. Thus viruses can involve membranes before the evolution of the complicated process of cell fission.

This will require the evolution of a lot of infrastructure. In biological terms: This is an interesting venture, but a speculative one; its not clear that cellular membranes are an inevitable development.

Game theory can shed light on RNA versus DNA in early organisms. Mutation is a crucial component of these games. It is the means by which alternative strategies are tested. With viral replication producing dozens of copies each generation, and needing only a few of those to be faithful replicas, viruses can tolerate high rates of mutation. As the chapter on Bacterial Evolution discusses, higher mutation rates lead to faster evolution. Thus organisms using RNA, which is less stable than DNA in cytoplasm, will be naturally selected.

The next chapter is The Evolution of Proteins

Copyright © 2005 Aubrey Jaffer

I am a guest and not a member of the MIT Computer Science and Artificial Intelligence Laboratory.  My actions and comments do not reflect in any way on MIT.
The Game Theory of Life
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