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Life could have begun when RNA molecules began to replicate. Now, science has finally found an RNA molecule that is very close to being able to do this: it is called QT45.
According to the “RNA world hypothesis”life began when RNA molecules evolved the ability to produce more copies of themselves.
A new study, this Thursday in Sciencediscovered an RNA molecule that is almost capable of this – it can carry out the essential steps involved, just not all at once.
“It was a long search until we reached the point where we were able to convince ourselves that RNA has the ability to produce itself under the right conditions,” said he, the leader of the research, Philipp Holliger from the MRC Laboratory of Molecular Biology, in Cambridge, United Kingdom, to .
The same magazine explains that in living cells, proteins perform fundamental tasks such as catalyzing chemical reactions, and the instructions for producing them are stored in double-stranded DNA molecules. RNA is a chemical relative of DNA that generally exists in the form of single chains.
It’s not as good at storing information as DNA because it’s less stable, but can do something DNA can’t: fold itself to form enzymes similar to proteins that can catalyze chemical reactions.
Because RNA can both store information and act as a catalyst, it was suggested as early as the 1960s that life could have begun with RNA molecules capable of catalyzing its own formation.
But Finding such molecules turned out to be really difficult.
Until… QT45 was discovered
RNA is made up of building blocks called nucleotides.
In the new study, the team started by generating a billion random sequences that were 20, 30 or 40 nucleotides long.
From these, they selected three that could carry out reactions such as joining nucleotides together. The three were brought together and subjected to several rounds of evolution – randomly changing, or mutating, parts of the sequence and selecting the best-performing variants.
The resulting molecule, called QT45is just 45 nucleotides long.
In alkaline water slightly above the freezing point, QT45 can use single-stranded RNA as a template to produce complementary chains by joining together small chains of two or three nucleotides, including producing a sequence complementary to its own.
A QT45 can also produce more copies of itself from these complementary chains.
“For the first time, a fragment of RNA can produce itself and its coding chain, and these are the two constituent reactions of self-replication”, praised Holliger.
Now the plan is to continue to evolve the molecule and experiment with conditions like freeze-thaw cycles to see if both reactions can occur simultaneously.
