Unraveling a Chemical Pathway to Ribonucleotides: Could Autocatalysis Have Played a Role in the Origin of Life?

Thursday - December 7 2023, 13:06 UTC - 11 months ago

Chemists are trying to recreate the chain of reactions required to form RNA at the dawn of life. Autocatalytic reactions, which produce chemicals that encourage the same reaction to happen again, could have played a part. A twist in the pathway to ribonucleotides could further increase the amount of useful molecules formed.

How did life begin? How did chemical reactions on the early Earth create complex, self-replicating structures that developed into living things as we know them? .

According to one school of thought, before the current era of DNA-based life, there was a kind of molecule called RNA (or ribonucleic acid). RNA—which is still a crucial component of life today—can replicate itself and catalyze other chemical reactions.

But RNA molecules themselves are made from smaller components called ribonucleotides. How would these building blocks have formed on the early Earth and then combined into RNA? .

Chemists like me are trying to recreate the chain of reactions required to form RNA at the dawn of life, but it’s a challenging task. We know whatever chemical reaction created ribonucleotides must have been able to happen in the messy, complicated environment found on our planet billions of years ago.

I have been studying whether "autocatalytic" reactions may have played a part. These are reactions that produce chemicals that encourage the same reaction to happen again, which means they can sustain themselves in a wide range of circumstances.

In our latest work, my colleagues and I have integrated autocatalysis into a well-known chemical pathway for producing the ribonucleotide building blocks, which could have plausibly happened with the simple molecules and complex conditions found on the early Earth.

The Formose Reaction .

Autocatalytic reactions play crucial roles in biology, from regulating our heartbeats to forming patterns on seashells. In fact, the replication of life itself, where one cell takes in nutrients and energy from the environment to produce two cells, is a particularly complicated example of autocatalysis.

A chemical reaction called the formose reaction, first discovered in 1861, is one of the best examples of an autocatalytic reaction that could have happened on the early Earth.

In essence, the formose reaction starts with one molecule of a simple compound called glycolaldehyde (made of hydrogen, carbon and oxygen) and ends with two. The mechanism relies on a constant supply of another simple compound called formaldehyde.

A reaction between glycolaldehyde and formaldehyde makes a bigger molecule, splitting off fragments that feed back into the reaction and keep it going. However, once the formaldehyde runs out, the reaction stops, and the products start to degrade from complex sugar molecules into tar.

The formose reaction shares some common ingredients with a well-known chemical pathway to make ribonucleotides, known as the Powner–Sutherland pathway. However, until now no one has tried to connect the two—with good reason.

The formose reaction is notorious for being "unselective." This means it produces a lot of useless molecules alongside the actual products you want.

An Autocatalytic Twist in the Pathway to Ribonucleotides .

In our study, we tried adding another simple molecule called cyanamide to the formose reaction. This makes it possible for some of the molecules made during the reaction to be "siphoned off" to produce ribonucleotides.

The reaction still does not produce a large quantity of ribonucleotides, but it works in a plausible way. Our research suggests that further tweaks and additions to the formose reaction could increase the amount of useful molecules formed.