Friday, November 25, 2016

Bringing silicon to life

Public Release: 24-Nov-2016
Bringing silicon to life
Scientists persuade nature to make silicon-carbon bonds
California Institute of Technology

A new study is the first to show that living organisms can be persuaded to make silicon-carbon bonds--something only chemists had done before. Scientists at Caltech "bred" a bacterial protein to make the man-made bonds--a finding that has applications in several industries.

Molecules with silicon-carbon, or organosilicon, compounds are found in pharmaceuticals as well as in many other products, including agricultural chemicals, paints, semiconductors, and computer and TV screens. Currently, these products are made synthetically, since the silicon-carbon bonds are not found in nature.

The new study demonstrates that biology can instead be used to manufacture these bonds in ways that are more environmentally friendly and potentially much less expensive.


The study is also the first to show that nature can adapt to incorporate silicon into carbon-based molecules, the building blocks of life. Scientists have long wondered if life on Earth could have evolved to be based on silicon instead of carbon. Science-fiction authors likewise have imagined alien worlds with silicon-based life, like the lumpy Horta creatures portrayed in an episode of the 1960s TV series Star Trek. Carbon and silicon are chemically very similar. They both can form bonds to four atoms simultaneously, making them well suited to form the long chains of molecules found in life, such as proteins and DNA.


The researchers used a method called directed evolution, pioneered by Arnold in the early 1990s, in which new and better enzymes are created in labs by artificial selection, similar to the way that breeders modify corn, cows, or cats. Enzymes are a class of proteins that catalyze, or facilitate, chemical reactions. The directed evolution process begins with an enzyme that scientists want to enhance. The DNA coding for the enzyme is mutated in more-or-less random ways, and the resulting enzymes are tested for a desired trait. The top-performing enzyme is then mutated again, and the process is repeated until an enzyme that performs much better than the original is created.

Directed evolution has been used for years to make enzymes for household products, like detergents; and for "green" sustainable routes to making pharmaceuticals, agricultural chemicals, and fuels.


As to the question of whether life can evolve to use silicon on its own, Arnold says that is up to nature. "This study shows how quickly nature can adapt to new challenges," she says. "The DNA-encoded catalytic machinery of the cell can rapidly learn to promote new chemical reactions when we provide new reagents and the appropriate incentive in the form of artificial selection. Nature could have done this herself if she cared to."

I looked up relative abundance of elements. Silicon is very abundant on earth, carbon rare, so I thought it might indicate that carbon was more suitable for life. Looking deeper, there is actually 7 times more carbon in the universe than silicon, but most of the carbon has been lost from earth in the form of volatile hydrocarbons, evaoprating into space. So carbon might have been more abundant at the time life was forming on earth.

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