Can Silicon-based Life Forms Exist?

Artistic view of organosilicon-based life. Image credits: Lei Chen/Yan Liang (BeautyOfScience.com)

Carbon is the primary building block of life. One of the main reasons which make carbon essential to our life on earth is its ability to make long carbon chained molecules. Take for example the DNA, the molecule that forms the basis of growth, development, functioning, reproduction and many more processes in all the living beings, has carbon as its backbone.

As well as this, carbon also forms the building blocks of the cell, the proteins.

Probably owing to so much importance, we have a lot of textbook chapters dedicated to carbon. But can carbon’s monopoly be challenged by silicon?

SILICON- CARBON LIKE PROPERTIES

Silicon is an element extremely similar to carbon. Being just one place beneath carbon in the periodic table, silicon shares many of carbons properties – especially the necessary ones that make carbon so relevant in life on Earth.

Silicon, like carbon, has 4 unpaired electrons on its outer shell that are readily available to form covalent bonds. It is also able to make long-chained molecules that bond to oxygen.

This leads to the question – is it possible for silicon-based life forms to exist?

Maybe something in tune of the popular science fiction, Horta from Star trek. Silicon-based life is perhaps the most common form of alternate biochemistry explored.

Silicon-based life form Horta
Silicon-based life form Horta, from Star trek. Image credits: Star trek

Frances Arnold, Prof. of Chemical Engineering at the California Institute of Technology in Pasadena, is the senior author of a study looking into this– a study that manually implemented evolutionary movements to see if the creation of carbon-silicon bonds was capable in a biological system.

DIRECTED EVOLUTION

This method is known as “directed evolution”. It is a protein engineering method that mimics the process of natural selection through a biased set of conditions to reach a specifically defined goal.

By using directed evolution to create enzymes that produce specific products, it cuts out the need for potentially complex and wasteful production methods. This can save a lot of time and money in the manufacturing process. It can also contribute less waste and hazardous chemicals into the environment.

This method has found applications in producing products ranging from fuels to pharmaceuticals, in a way that is much more efficient and cleaner for the environment.

“Nature does the actual chemistry much better and can make molecules that human chemists have not yet figured out how to make,” Arnold explains.

FORMATION OF CARBON-SILICON BONDS

Many of the enzymes that the authors had available were capable of catalyzing the formation of carbon-silicon bonds. However, most of them only resulted in the formation of weak bonds.

One specific protein, Rhodothermus Marinus, which originated from a bacterium in Iceland, was chosen because of its ability to effectively and selectively form this bond.

The enzymes were constantly mutated and then tested to see if they were performing well in the catalyzation of these silicon-carbon bonds. This was done until they deemed the enzyme proficient at forming the bond.

My laboratory uses evolution to design new enzymes,” explained Arnold. “No one really knows how to design them, they are tremendously complicated. But we are learning how to use evolution to make new ones, just as nature does.

This study also showed that the E. coli bacteria could create these organosilicon compounds after being mutated to contain the altered form of Rhodothermus Marinus.

“We provide the opportunities which do not exist in nature in the laboratory and found that they can actually do things nature has never discovered before.” explains Sek Bik Jennifer Kan, a postdoctoral scholar in chemical engineering.

With the formation of carbon-silicon bond, the study proved to be a success. With an insertion of carbine into the silicon-hydrogen bonds, the heme proteins were able to catalyze the organosilicon compounds’ formation.

ORGANOSILICON COMPOUNDS

Reportedly, this method forms significantly less undesirable by-products. It formed silicon bonds 15 times more efficiently than the best synthetic techniques available.

It is by far a quicker and cleaner way of producing organosilicon compounds. This has already led to multiple companies needing to apply Arnold’s results to mass production.

HOPE FOR SILICON-BASED LIFE

Whilst these findings are a breakthrough in the production of organosilicon compounds, it, unfortunately, doesn’t help to prove or disprove whether silicon-based extra-terrestrial life is a possibility or not.

There are problems that arise with substituting carbon with silicon when it comes to the possibility of life.

Silicon bonded to other silicon atoms is usually a weaker bond than when carbon bonds to itself. These silicon-silicon bonds are also usually unstable when they’re around oxygen.

This suggests that, if silicon-based life was possible, it wouldn’t be anywhere near as complex as carbon based life.

Whilst this may be disconcerting to the hopefuls wanting to eventually come across silicon-based life, it does pose a potentially promising theory – if enzymes were able to create carbon-silicon bonds in a laboratory, does this mean that, somewhere on a distant planet, natural selection and evolution naturally took this path and created silicon-based life?

Video Credits: Youtube/Caltech

Read more about this research here.

Source Science Caltech

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