For the past 120 years, the Nobel Prize has honored scientists for discoveries that the
committee feels most benefit mankind.
And today we’re going to talk about this year’s winners for Physics and Chemistry,
whose discoveries are solving the mysteries of both the universe and our DNA.
The Nobel Prize for Physics was awarded to Takaaki Kajita and Arthur B. McDonald, who
led separate teams of scientists that each proved neutrinos have mass.
Neutrinos are subatomic particles produced when radioactive elements decay.
They’re the second most abundant particle in the universe, after photons.
Billions are streaming through you right now!
We know there are at least three flavors, or types of neutrinos: electron, muon, and
tau, all named after which charged particles they can interact with.
But they’re so difficult to detect that they’re incredibly hard to study.
It’s just hard to catch one so we can look at it.
So if neutrinos are so hard to detect, how did Kajita and McDonald make their discoveries?
Both scientists work in teams attached to a neutrino detector.
Kajita works with the Super-Kamiokande detector in Japan, and McDonald works with the Sudbury
Neutrino Observatory in Canada.
Both detectors work in pretty much the same way, looking for the tiny flashes neutrinos
make when they pass by protons and electrons in just the right way.
For a long time, scientists thought the flavor of a neutrino was built-in, and never changed.
By studying the flashes of light observed in the Super-Kamiokande detector, Kajita discovered
in 1998 that muon neutrinos were turning into electron neutrinos, and then back to muon
neutrinos as they travelled.
A few years earlier, McDonald’s team had found that about two thirds of the neutrinos
from the sun -- which all start out as electron neutrinos -- were changing into muon or tau
neutrinos on their way to Earth.
Now, according to quantum theory, neutrinos should only be able to change flavor if they
have mass.
Not a LOT of mass: the new data suggests that the upper limit is about 1/1000th the mass
of an electron.
But the fact that they have mass at all means that there are major things we don’t know
about some of the most abundant particles in the universe.
And neutrinos are now a real contender for dark matter, the universe’s so-called “missing”
mass.
The Nobel Prize for Chemistry was awarded to three scientists - again, all part of separate
teams - who helped figure out how the cells in your body repair damaged DNA.
DNA is fragile.
Our genetic material is constantly damaged -- up to 10,000 times per day, per cell.
There is no way life based on such a fragile molecule could exist if your cells couldn’t
repair that damage.
It turns out that different types of DNA damage are repaired by different mechanisms in your
cells.
Tomas Lindahl’s work in 1974 led to the discovery of Base Excision Repair, the mechanism
that repairs the most common type of damage, which is spontaneous decay of one of the bases
that make up our genetic code.
For example, cytosine -- the DNA base that normally pairs with guanine -- can spontaneously
lose part of its molecule to form uracil.
This happens all the time, actually.
And when it happens, the newly-formed uracil pairs with adenine instead, so that section
of DNA looks all different
Lindahl discovered the first DNA Glycosylases: repair proteins that remove the damaged or
wrong bases.
These proteins recognize specific types of DNA damage, clip them out of the DNA strand,
and replace them with their original bases -- so if, say, they see a uracil bonded to
an adenine, they’ll know to replace it with a cytosine.
In 1992, Aziz Sancar discovered another way our bodies fix DNA, called Nucleotide Excision
Repair.
It takes care of damage to DNA done by UV rays, as well as chemical substances that
cause mutations, like nicotine.
That kind of damage changes the shape of the DNA helix, so NER removes not just the base,
but the entire nucleotide, which is the base plus the backbone of the helix it’s attached
to.
Sancar found that an enzyme known as an exonuclease cuts out the damage, taking a piece about
12 nucleotides long in total.
He then mapped out how two other enzymes are involved: DNA polymerase, which fills in the
gap, and DNA ligase, which stitches the pieces back together.
The DNA of a normal skin cell exposed to sunlight would end up with thousands of errors every
day, if this process didn’t remove them!
The third winner, Paul Modrich, discovered Mismatch Repair in 1989, which is exactly
what it sounds like -- it repairs mismatched bases introduced to a strand of DNA during
cell division.
DNA ‘proofreading’ during cell division is very good, but not perfect.
About one in every one hundred million bases is copied incorrectly, and MMR fixes 99.9%
of those.
Modrich demonstrated how an enzyme called Dam methylase marks damaged DNA, which shows
other enzymes which pieces to cut out.
Then, DNA polymerase and ligase again fill in and repair the cut strand.
But scientists still don’t know how the enzyme knows which strand needs to be repaired.
Thanks to this year’s winners, though, we do know a lot more about how our bodies keep
their genetic instructions clear -- plus, we have a few more clues about how the universe
works.
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