DNA Replication Footage Reveals New Facts
In a world first, researchers have recorded close up footage of a single DNA molecule replicating itself, causing us to question the way we assumed this process to play out.
The footage has revealed that this fundamental part of life incorporates an unexpected amount of “randomness”, and it could force a major rethink into how genetic replication occurs without mutations, writes Business Insider UK.
Team member, Stephen Kowalczykowski from the University of California, Davis, said, “It’s a real paradigm shift, and undermines a great deal of what’s in the textbooks. It’s a different way of thinking about replication that raises new questions.”
Scientists have always assumed that the DNA polymerases on the leading and lagging strands of the double helices somehow coordinate with each other throughout the replication process so that one does not get ahead of the other during the unravelling process and cause mutations.
However, the new footage reveals that there’s, in fact, no coordination at all, and somehow, each strand acts independently of the other and still results in a perfect match each time. The team extracted single DNA molecules from E.coli bacteria and observed them on a glass side. They then applied a dye that would stick to a completed double helix, but not a single strand, which means they could follow the progress of one double helix as it formed two new double helices.
The team found that on average, the speed at which the two strands replicated was about equal, but throughout the process, there were surprising stops and starts as they acted like two separate entities on their own timelines.
The lagging strand also stopped synthesising at times, but the leading strand continued to grow. Other times, one strand would start replicating at ten times its regular speed, for no particular reason.
Kowalczykowski, explained, “We’ve shown that there is no coordination between the strands. They are completely autonomous.”
Due to the lack of coordination, the DNA double helix has had to incorporate a ‘dead man’s switch’, which would kick in and stop the helicase from unzipping any further so that the polymerase can catch up.
With the two stands “functioning independently” as the footage suggests, how does the unravelling double helix know how to keep things on track and minimise mutations by hitting the breaks or speeding up at the right time?
We are hopeful that more real-time footage such as this will helps scientists discover more about the process such as this.