
DNA Replication Filmed for the First Time, and it's not what we expected - Tomte
http://www.sciencealert.com/dna-replication-has-been-filmed-for-the-first-time-and-it-s-stranger-than-we-thought
======
moh_maya
[http://dx.doi.org/10.1016/j.cell.2017.05.041](http://dx.doi.org/10.1016/j.cell.2017.05.041)

Original paper link. Sci-hub ought to be able to get you the paper.

On first pass, seems like this is an in-vitro study. I would hesitate to go
from "we didn't observe what we expected to see, while performing a limited,
highly abstracted experiment on a glass slide" to "based on this, everything
we understand about what actually happens inside a cell now has to change" .
The article on SA feels a bit over the top.

------
sctb
Discussed at the time:
[https://news.ycombinator.com/item?id=14591751](https://news.ycombinator.com/item?id=14591751)

------
nerdponx
How do I interpret the video? It just looks like dots and lines, to my
untrained eye I have no idea how it relates to the article.

~~~
moh_maya
So, the authors used a fluorescent dye that only fluoresces when it is part of
double stranded DNA.

The surface is a glass slide / coverslip on which you have DNA + the DNA
replication enzymes (not the entire set used inside a cell... Just the most
important ones for the actual process of DNA replication).

They used a technique called tirf microscopy [1] which allows them to, in
effect, monitor only the molecules and dyes adhered to the surface plane they
want to observe.

The lines are, at a simplistic level, single stranded DNA getting converted to
double stranded DNA.. as the DNA gets replicated, the dye fluoresces. As the
replication proceeds and the replicated length increases, more of the dye gets
incorporated into double stranded DNA and starts fluorescing, acting as an
indicator of ds-DNA formation, and therefore, a proxy for DNA replication
success in this experimental model.

The dots ( if I am interpreting correctly) are the template DNA in circular
form.

It's a very cool technical achievement in itself, getting this system to work!

[1] [http://www.leica-microsystems.com/science-lab/total-
internal...](http://www.leica-microsystems.com/science-lab/total-internal-
reflection-fluorescence-tirf-microscopy/)

------
singularity2001
In one sentence the strands act "independently", in the next sentence they are
synchronizing via halts and speed ups. What am I missing?

~~~
icegreentea2
It's a bit subtle. What they found is that the polymerease step (the actual
duplication) is independent, but the helicase step (this unwinds the original
double strand DNA) has some sort of mechanism to limit the difference between
the two strands.

