Chapter 18: Life On Earth

List of symbols that represents BioBrick parts. BioBricks are DNA sequences which conform to a restriction-enzyme assembly standard

It's natural to wonder about the role of chance or contingency in biology itself. Rather than serendipitous, it’s more accurate to say that life on Earth has been very selective. It depends on only two dozen of the elements in the periodic table, works with only one of the two possible orientations ("handedness") of building block molecules, and it uses a single type molecule to code genetic information. It employs only 20 amino acids from among thousands available and ten thousand proteins from among an essentially infinite number that is possible. Are these selections inevitable? Could they have been made differently? How do we begin to examine the sufficient and necessary conditions for life?

Biologist Drew Endy

Tweaking fundamental biochemistry that has been in place for four billion years is radical. An even more audacious approach involves inventing entirely novel tools for the toolbox or building life from the ground up. In 2000, scientists inserted two devices into the innocuous bacterium E. coli, a bacterium that lives in the human gut. A group at Princeton put together three interacting genes in a way that made the bacteria emit light blink regularly, like Christmas tree lights. Meanwhile, a group in Boston set up two genes to interfere with each other functions. In doing so, they created the equivalent of a toggle switch and endowed E. coli with a rudimentary digital memory. Essentially they used a biochemical means to control a set of on-off states as opposed to a semiconductor where the same thing is done with a flow of electrons. It took years to develop these tricks, but MIT biologist Drew Endy foresees a time when manmade biological mechanisms may far outnumber the products of eons of natural selection. Endy is the inventor of BioBricks. They don’t look that impressive—the dozens of vials on Endy’s desk seem to contain only clear, viscous liquid—but they represent a revolution in the making. Each BioBrick is a chunk of DNA that, when inserted into a cell, causes a protein to do something useful. They’re standardized so that they send and receive the same biochemical signals and interact well with each other. Endy and his colleague Thomas Knight have created a registry of over 20,000 different BioBricks, and they make them freely available to other researchers.

 Organic chemist, Eckard Wimmer

Making components for “squishy” computers that work millions of times slower than the silicon kind doesn’t seem very promising, but the eventual goal is to engineer functions into living organisms. The researchers encounter the problem of persistence. Their tiny devices have to work in the busy and messy world of a cell, not in a sterile vial on a lab bench. In the world of the cell, they tend to mutate and break. How far can we take the idea of building life? Eckard Wimmer stunned the world in 2002 when he announced that he and his team had built a live poliovirus from mail-order segments of DNA and a genome map that’s freely available on the Internet. The implications for bioterrorism are obvious — what if someone could synthesize Ebola, smallpox, or anthrax? Even worse, what if synthesized germs could be endowed with resistance to antibiotics? The rate of progress is dizzying. Genome icon Craig Venter put together a virus that infects bacteria. It only took him three weeks to do what had taken Wimmer three years. In 2016, scientists created a single-celled, synthetic organism that only had 473 genes, making it the simplest living cell ever known. The era of synthetic biology has arrived.