How does prebiotic chemistry help us to understand how life started?

Let’s start by defining prebiotic chemistry as chemical reactions that happened before the emergence of life as we know it. There are many theories for the origins of life on Earth, but we have yet to connect all the dots to complete the story. One theory as to how life originated on our planet points to an “RNA World” where molecules of the genetic polymer RNA (Ribo Nucleic Acid – similar to DNA, Deoxyribo Nucleic Acid) formed. According to this theory, these molecules of RNA had the ability to copy themselves and were later encapsulated by lipids (certain types of organic molecules) to form what we call “proto cells.”

Here we ask the question: where did the RNA come from in the first place? To answer this question, we study the structure of nucleotides, the building blocks of RNA. A nucleotide has three components: a sugar (ribose), a phosphate, and a heterocycle (a certain type of organic compound). Let’s focus on one of these components, ribose (a molecule of this sugar has five carbon atoms).

Chemists are interested in what kind of molecules might have been present on the early Earth or in interstellar space, billions of years ago, to assess what chemical building blocks for life might have been available to start with. To gain a better understanding of what molecules can be added to my toolbox of prebiotic chemistry, we collaborate. We ask fellow scientists – astrochemists, geochemists & geologists – who have a better understanding of what is out in deep space and what may have been on the early Earth, when the planet cooled just enough to enable water to be liquid on its surface.

For example, astrochemists have confirmed the presence of simple organic molecules such as formaldehyde, glycolaldehyde, and glyceraldehyde in interstellar gas clouds. These three molecules contain one, two and three atoms of carbon respectively. Using chemistry, we can mix these molecules in the lab in various ratios, at different temperatures, and at varying pH levels, and we can include a variety of elements or minerals that we think were present on an early Earth. One prebiotic chemistry experiment, for example, showed that we could mix these simple organic molecules with borate to form stable sugars including the five-carbon ribose. Another molecule present in interstellar gas clouds is cyanide, which can undergo a chemical reaction to evolve into the heterocyclic molecule adenine. Here we now have two pieces of a nucleotide. The next step is to understand how these molecules join together to form the backbone or RNA.

One perk of being an astrobiologist is the opportunity to collaborate with scientists in other fields and the perpetual learning we all engage in while we answer some of the most important questions relating to our own existence.