The spooky world of quantum mechanics might reach out and touch you — by mutating your DNA. Welcome to the weird world of quantum biology.
Could quantum mechanics — a field that Albert Einstein once
derided as “spooky” — affect us in a highly personal way? Quite possibly.
Theoretical research is beginning to suggest that quantum effects could drive
mutations in human DNA. If true, this could change how we understand cancer,
genetic disease, and even the origins of life.
Scientists once thought biological systems too warm, wet,
and chaotic to experience weird quantum effects like proton tunneling, in which
the particle’s waveform spreads out, allowing it to blip across an energy
barrier that would normally block its passage. Generally, the more heat and
chaos around, the smaller the quantum effect; so, for many years, scientists
thought that in the human body quantum behaviors would be too small to matter.
But you can’t find what you aren’t looking for. As quantum
physicists start to poke at the messy and complex world of biology, they are
finding quantum mechanics at play, even within our DNA. Welcome to the world of
quantum biology.
A primer on point mutations
The iconic double helix of DNA is formed by two coiling
molecular strands with bits at the center that connect like puzzle pieces, each
with one of four different shapes, named with a letter. T shapes bond to A
shapes, and G shapes connect with C shapes, forming what are known as “base-pairs.”
These little molecular branches connect through weak attractions between their
hydrogen atoms, which have a single proton and electron.
Sometimes, an error occurs and the letters are paired
incorrectly — a mistake we call a point mutation. Point mutations can add up
and cause problems with DNA, sometimes leading to cancer or other health
problems. Most often the result of mistakes during DNA replication, point
mutations also can be caused by X-ray exposure, UV radiation, or anything that
excites atomic particles to move from their orderly places.
Quantum biology
For 50 years, researchers have debated whether protons
switching positions between weakly bound strands of DNA could cause point
mutations. The answer seemed like no. Many studies have concluded that the
intermediate base-pair states created by proton switching were too unstable and
short-lived to be replicated in the DNA. But a new study published in the
journal Communications Physics finds that these states can be frequent and
stable, and that quantum processes may drive their formation.
The researchers modeled proton transfer between hydrogen
bonds of the G:C base-pair in an infinite sea of spring-like vibrating
particles, representing the chaotic cellular environment. Their calculations
show that proton transfer through quantum tunnelling can happen very quickly
for G:C connections at the center of a DNA helix — within a few hundred
femtoseconds, or 0.000000000000001 seconds. Such a rate is much faster than our
biological timescale.
This switching happens so fast and so often that to our DNA,
it “appears” like a proportion of protons are always visiting their neighbors,
in the same way that an image on a screen can flash so quickly it looks still
to our eyes. This super-fast switching of protons from one side of the bridge
to the other means that base-pairs are constantly changing between their
original form and a slightly different shape. These intermediate forms can
cause a mismatch during DNA replication, when the strands are opened, read, and
copied.
Instead of preventing protons from tunnelling, our
biological warmth may act as a source of thermal activation, giving protons
enough energy to pop over to the other side. Indeed, proton transfer through
quantum tunnelling is four times more likely than predicted by classical
physics. Not only are these occurrences common, but they are also long-lived.
Based on previous computational studies, the researchers predict that these
molecular changes should be stable long enough to be replicated — causing a
mutation.
There are two primary limitations with the work. First, the
researchers did not investigate A:T base-pairs, noting that for these bonds,
the intermediate state is highly unstable and not as likely to play a role in
DNA mutations. Second, this theoretical work would benefit from experimental
tests to validate or challenge the results.
A quantum of solace?
Based on the team’s calculations, point mutations should
appear in our DNA much more frequently than they do. The researchers attribute
this difference to “highly efficient DNA repair mechanisms” that find and undo
the damage. For instance, our DNA replication machinery includes a
“proofreading” ability, in which mistakes are detected and corrected — sort of
like a typo. Thank goodness for biological copy editors.
The ease of proton tunnelling and the longevity of these
intermediate states might even be relevant to studies on the origin of life,
the researchers write, because the rate of early evolution is linked to the
mutation rate of single-stranded RNA. Thus, though the quantum world might seem
weird and distant, it might have played a role in giving us life — and also
taking it away.
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