Thanks for allowing me to participate in the Emergence photo group and discussions. My contribution is not a photo, but a figure describing simulations from a recent paper. I have a lot of nature photos that show emergent patterns and I hope to share these with you, but I figured I would start with this material since it is a direct demonstration of emergence (loosely defined here as the creation of simple patterns from a complex set of rules).

You may be aware that amino acids, the building blocks of proteins in our body, share the same chirality or handedness of chemical structure. While it is unclear how this homochirality evolved out of a primordial mixture of left and right-handed amino acids, we know today that homochirality is an important component of regular secondary structures found in many proteins such as the alpha-helix, shown above, the beta-sheet and others.

However, there are a few cases where organisms will synthesize heterochiral peptides through special synthetic pathways - these often function as toxins or antimicrobials - because of their deviation from natural chemical structure - host defense mechanisms often cannot adapt to these chemicals.

The above figures show a simulation of a short 11-residue protein chain docking against an alpha helix. When a poly-alanine chain is allowed to vary both its conformation (bending, twisting) and the chirality of individual positions - the simulation consistently minimizes to a homochiral helix, either with a left handed twist or a right handed twist. This is amazing considering this is only one of 2^11 possible solutions.

Proteins are great examples of emergent structure. Evolution has tuned them to resolve a well defined structure quickly. It appears homochirality is one property that favors fast folding, stable proteins. Hence, homochirality seems to be an emergent property of protein evolution.

For more info, contact me, or see:

Nanda & DeGrado "Simulated Evolution of Emergent Chiral Structures in Polyalanine", Journal of the American Chemical Society, 2004