The missing molecule of life’s building blocks

Our genetic blueprint could have brewed up in space, an international team of scientists has discovered. While exposing chemicals to comet-like conditions in a laboratory, they produced a sugar essential to our genetic material. The finding sheds light on how life may have emerged on Earth.

Life first stirred on our planet four billion years ago, but scientists debate about where its building blocks were cooked up.

Finding out matters – if life’s ingredients formed in space and were transported to Earth, they may well have been transported elsewhere in the Universe.

The theory that life’s building blocks smashed down with comets has found support, as molecules such as amino acids (protein units) and nitrogenous bases (components of our genetic material) have been discovered in meteorites, or in comet-like conditions in the lab.

But one molecule has not been spotted – ribose, a sugar which forms the essential backbone of RNA, the genetic material found in all living organisms and some viruses on Earth.

The authors of this study managed to cook up ribose in the conditions of a forming comet.

Simulating the ice-coated dust grains that would have once built up to comets during the birth of the Solar system, the scientists placed raw materials – a mix of water, methanol and ammonia – in a high vacuum chamber chilled to -200 °C.

The researchers shone UV light on the mixture and heated the concoction to room temperature, as a comet approaching the Sun could be warmed.

When the scientists analysed their artificial comet’s brew, they discovered different sugars, including the elusive ribose. Further, the sugars were soluble in water – crucial for if they were ever to react with other molecules to form more complex structures and life.

The team’s data suggest this ribose formed from a chemical called formaldehyde. While ribose remains to be detected on comets, formaldehyde has already been sniffed out by, among others, the Rosetta mission to Comet 67P.

The findings have produced “plausible insight” for how interstellar chemistry could lead to life on suitable planets, the authors say.

But the questions don’t end there, wrote Mars Exploration Rover Science Team collaborator Christian Schröder for The Conversation UK.

“Could one of the other types of sugar have led to the creation of some kind of life form with a different coding mechanism to RNA? […] And are specific mineral surfaces needed in this process?

“Tackling these questions is the exciting ongoing step in the quest to understand whether widespread occurrence of the building blocks of life in the universe means the existence of actual life beyond Earth.”

The findings were published in Science.

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