How to think about… Life | Tech News

What distinguishes a human from a virus from an inert rock? There are many definitions for what it means to be alive – and soon humanity might fail some

life

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MOST people agree that for something to be alive, it must be able to make copies of itself. But by that rationale, a crystal growing in a is alive. So biologists studying how life began 4 billion years ago look for characteristics shared by all living things and absent in minerals.

This approach yields three distinct features: all organisms on Earth have a code that, like a builder’s blueprint, allows copies to be made (see “How to think about… Genes”); they can generate energy to power the copying process; and they have the machinery to build the copies. Crystals have none of these, so are firmly dispatched to the realm of minerals.

This list kicks up other sticking points, however – notably certain parasites. Viruses, the ultimate example, have a code in the shape of DNA or RNA, but rely entirely on the cells they have invaded for energy and copying machinery. The debate over whether they are alive is decades old.

Synthetic biology raises even more basic questions. Floyd Romesberg at the Scripps Research Institute in San Diego has spent 20 years trying to hack life’s code. His team has created two “unnatural” genetic letters similar in molecular structure to the five used in all living organisms on Earth: four in DNA and an additional one in RNA. Last year, they used this unnatural code to coax a cell to produce proteins not found in nature. …

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