Sugar, spice and the origin of life: new theory for the first sugars

Living things are made of complex organic molecules – so where did those complex molecules come from?

Origin-of-life chemists have a suite of theories for how the first living molecules formed. Amino acids and nucleobases, which are key parts of proteins and DNA respectively, have fairly well-established beginnings. But sugars – another key part of DNA and RNA – are less well understood.

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It’s commonly thought that they may have started with a compound called formaldehyde (CH2O).

A pair of US researchers have suggested a different theory: published in Chem, they think that a compound called glyoxylate (C2HO3) is the more likely culprit.

Glyoxylate has featured in other origin-of-life theories too, as a basis for a number of other molecules crucial for life.

“We show that our new hypothesis has key advantages over the more traditional view that early sugars arose from the chemical formaldehyde,” says Professor Ramanarayanan Krishnamurthy, from the Department of Chemistry at Scripps Research Institute, US.

“The formaldehyde reactions proposed by this theory are quite messy – they have uncontrolled side reactions and other drawbacks due to formaldehyde’s high reactivity under the envisioned early-Earth conditions,” says Professor Charles Liotta, an emeritus professor at the Georgia Institute of Technology’s School of Chemistry and Biochemistry.

Instead, the researchers’ “glyoxylose reaction” starts with glyoxylate first reacting with itself, then with its own by-products in a chain until they become complex enough to form sugars.

Glyoxylate molecule surrounded by sugars
In this theory, glyoxylate – picture in the centre – reacts with itself and then with byproducts, eventually forming simple sugars (pictured, surrounding). Credit: Scripps Research and Unsplash

While they’ve worked out a series of chemical reactions that make sense in theory, the researchers haven’t shown that this works in a laboratory yet: that’s next on their list.

 “Such a demonstration would expand the role of glyoxylate as a versatile molecule in prebiotic chemistry and further stimulate the search for its own origin on the prebiotic Earth,” says Krishnamurthy.

This reaction also consumes CO2, meaning that – if it does work in practice – it could be a very effective carbon capture method.

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