Where did DNA come from? — Genetics Unzipped

The planet looks very different to the one we know today. Of course, with no life, there are no trees, plants, or animals. There’s also no oxygen or ozone layer, leaving the planet’s surface exposed to the sun’s intense UV rays and making it blisteringly hot. Despite the high temperatures, there are vast oceans covering most of the surface of the Earth . Frequent volcanic eruptions spew gases into the atmosphere, including carbon dioxide, nitrogen, hydrogen and water vapour. Not a great place to be, by any standards.

Experts think that the first step towards life was simply a molecule that was capable of self-replicating. As a geneticist, your mind might jump straight away to the most famous self-replicating molecule of them all, DNA. However, there has been plenty of debate about exactly which biological molecule filled this role, with many pointing to RNA as the prime candidate for the first replicator thanks to its versatility that allows it to self-replicate and store information - this is the basis of the so-called RNA world hypothesis.

RNA is a single-stranded biological polymer made up of building blocks called nucleotides. Nucleotides consist of a ribose sugar molecule attached to a phosphate group and a nitrogen-containing base. The bases in RNA are adenine, cytosine, guanine and uracil, usually known by their initials, A, C, G and U, strung together along a phosphate sugar backbone. And it’s the order of these nucleotides, or letters, that spell out the genetic code.

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