Theoretical physicists have confirmed that it's not just the information coded into our DNA that shapes who we are - it's also the way DNA folds itself that controls which genes are expressed inside our bodies.
That's
something biologists have known for years, and they've even been able to figure
out some of the proteins responsible for folding up DNA. But now a group of
physicists have been able to demonstrate for the first time through simulations
how this hidden information controls our evolution.
Let's back
up for a second here, because although it's not necessarily news to many
scientists, this second level of DNA information might not be something you're
familiar with.
As you
probably learnt in high school, Watson and Crick discovered in 1953 the double
helix structure of DNA. Since then we've learnt that the DNA code that
determines who we are is made up of a sequence of the letters G, A, C, and T.
The order of
these letters determines which proteins are made in our cells. So, if you have
brown eyes, it's because your DNA contains a particular series of letters that
encodes for a protein that makes the dark pigment inside your iris.
But that's
not the whole story, because all the cells in your body start out with the
exact same DNA code, but every organ has a very different function - your
stomach cells don't need to produce the brown eye protein, but they do need to
produce digestive enzymes. So how does that work?
Since the '80s, scientists have found that the way DNA is folded up inside our cells
actually controls this process. Environmental factors can play a big role in
this process too, with things like stress known to turn certain genes on and off through something known as epigenetics.
But the
mechanics of the DNA folding is an incredibly important control mechanism.
That's because every single cell in our body contains around 2 metres of DNA,
so to fit inside us, it has to be tightly wrapped up into a bundle called a
nucleosome - like a thread around a spool.
And the way
the DNA is wrapped up controls which genes are 'read' by the rest of the cell -
genes that are all wrapped on the inside won't be expressed as proteins, but
those on the outside will. This explains why different cells have the same DNA
but different functions.
In recent
years, biologists have even started to isolate the mechanical cues that
determine the way DNA is folded, by 'grabbing onto' certain parts of the
genetic code or changing the shape of the 'spool' the DNA is wrapped around.
So far, so
good, but what do theoretical physicists have to do with all this?
A team from
Leiden University in the Netherlands has now been able to step back and look at
the process on a whole-genome scale, and back up through computer simulations
that these mechanical cues are actually coded into our DNA.
The
physicists, led by Helmut Schiessel, did this by simulating the genomes of both
baker's yeast and fission yeast, and then randomly assigning them a second
level of DNA information, complete with mechanical cues.
They were
able to show that these cues affected how the DNA was folded and which proteins
are expressed - further evidence that the mechanics of DNA are written into our
DNA, and they're just as important in our evolution as the code itself.
This means
the researchers have shown that there's more than one way that DNA mutations
can affect us: by changing the letters in our DNA, or simply by changing the
mechanical cues that arrange the way a strand is folded.
"The mechanics of the DNA structure can change, resulting in different packaging and levels of DNA accessibility," they explain, "and therefore differing frequency of production of that protein."
Again, this
is simply backing up what many biologists already knew, but what's really
exciting from a purely speculative point of view is the fact that the computer
simulations open up the possibility for scientists to model and maybe one day
even manipulate the mechanical cues that shape our genetic code.
There's no
evidence that we can do that just yet, but what we do know is that the more
scientists understand about how our DNA is controlled and folded, the closer we
get to being able to improve upon it.
The research
has been published in PLOS ONE.
Comments
Post a Comment