“Here’s proof of how far we’ve come in science - in a world-first, researchers have recorded up-close footage of a single DNA molecule replicating itself, and it’s raising questions about how we assumed the process played out.The real-time 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.”
HOW IT WORKS:
“The DNA double helix consists of two intertwining strands of genetic material made up of four different bases - guanine, thymine, cytosine, and adenine (G, T, C and A).Replication occurs when an enzyme called helicase unwinds and unzips the double helix into two single strands.A second enzyme called primase attaches a 'primer’ to each of these unravelled strands, and a third enzyme called DNA polymerase attaches at this primer, and adds additional bases to form a whole new double helix.”
WHY THIS IS WEIRD AND NOT WHAT WE EXPECTED:
“The fact that double helices are formed from two stands running in opposite directions means that one of these strands is known as the 'leading strand’, which winds around first, and the other is the 'lagging strand’, which follows the leader.The new genetic material that’s attached to each one during the replication process is an exact match to what was on its original partner.So as the leading strand detaches, the enzymes add bases that are identical to those on the original lagging stand, and as the lagging strand detaches, we get material that’s identical to the original leading strand.
Scientists have long assumed that the DNA polymerases on the leading and lagging strands somehow coordinate with each other throughout the replication process, so that one does not get ahead of the other during the unraveling process and cause mutations. But this new footage reveals that there’s no coordination at play here at all - somehow, each strand acts independently of the other, and still results in a perfect match each time.“
Source & further reading:https://www.eurekalert.org/pub_releases/2017-06/uoc--vio061317.php
Journal article:http://www.cell.com/cell/fulltext/S0092-8674(17)30634-7?_returnURL=http%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0092867417306347%3Fshowall%3Dtrue
Gif:
Each glowing strand is a piece of double helix growing by replication at the left-hand end. They move at different speeds and stop and start. Dark gaps in the line are single-stranded DNA where one polymerase failed to attach (the fluorescent dye only binds double-stranded DNA).
Some surprises come out of being able to observe replication directly. For example, the two polymerases involved in replication (one for each strand) aren't coordinated. They stop and start at random, but overall they move at the same average speed, so everything works out. This stochastic model is quite different from a smooth-running, coordinated machine usually imagined.
CREDIT: James Graham, UC Davis
Source: Corina Marinescu
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