This is Hell Creek, Montana. 68 million years ago, a small T rex died somewhere around here, and over time, minerals replaced
its bones which turned its body into a T rex fossil.
In the year 2000, scientists dug it out of the ground, and shipped some of it to a museum,
and some of it to a paleontologist named Mary Schweitzer.
When she first saw those bone samples, she noticed that they looked a little different
than normal bone.
So she put the sample in an acidic solution hoping to reveal some of the deeper bony structures.
After a few days, the sample had completely demineralized.
But it left something interesting, a bendable, fibrous substance that looked like blood vessels
and a tough connective tissue called collagen — some of the kinds of soft tissues you’d
see in normal bones..
/That/ was not supposed to be possible.
Up until this point, we’d only seen /evidence/ of soft tissue, not intact soft tissue.
It was thought that this kind of tissue would get disintegrated really quickly after the
organism died, but here they were millions of years later.
Naturally, the paleontology community was a little skeptical, so to prove her point.
Shweitzer dipped her vintage collagen in a very specific enzyme called collagenase, and
the collagen that stayed strong for 68 million years dissolved in half an hour.
And some scientists think enzymes like collagenase might work because of quantum physics.
But how do they know that?
First some background.
Left by itself, collagen will break down eventually.
But adding an enzyme makes that breakdown process happen over a trillion times faster.
And that’s enzymes’ whole thing.
They speed up chemical processes by a lot.
Look at one process that we do all the time: our cells consume oxygen and produce carbon
dioxide as a byproduct, A little bit of that CO2 dissolves in the
blood, some attaches to the hemoglobin in our red blood cells, but most of it gets converted
into carbonic acid so it can be transported to the lungs and breathed out.
Again, that conversion can happen unassisted, but we have a lot of these CO2 molecules to
get rid of, so we need to find a way to do a lot of it and do it fast.
Without a catalyst, this reaction happens about once every ten seconds.
But add an enzyme called carbonic anhydrase, and now it happens a hundred thousand times
every second, that’s about a million times faster than without the enzyme.
Enzymes are so useful because they can speed up chemical reactions, from the ones we use
in our day to day physiology to the ones we try to manipulate through pharmaceuticals.
ACE inhibitors like benazepril or lisinopril are common blood pressure medications.
ACE stands for angiotensin converting enzyme, angio for vessel, tensin for tension, or pressure.
So when angiotensin is converted via this enzyme, it tightens up blood vessels.
By inhibiting this enzyme, you’re encouraging the blood vessels to dilate and lower blood
pressure and that’s what these drugs do.
There ya go.
They’re not just useful for dinosaur tissues.
Enzymes are everywhere!
And you can usually spot enzymes because they end in -ase.
Lipase, helicase, maltase.
All are enzymes and end in -ase.
And those prefixes usually tells you what they do.
Lipase breaks down lipids.
Helicase unravels the DNA helix.
And Maltase breaks maltose into glucose.
No matter what enzyme in the human body you’re looking at, they all make biological processes
happen faster.
And for decades, classical mechanics has offered a totally reasonable explanation for how they
work.
Big picture here — some of our physiology requires energy to go from reactants to products.
We often use this graph with energy on the y axis and the completion of the reaction
on the x axis.
Without the energy to get over this hill, the reaction won’t happen.
In 1948, an American scientist named Linus Pauling had the idea that enzymes can lower
the energy hill because of how they fit together in something called transition state binding.
See, each enzyme is specially built to bind to one particular reactant, or substrate,
kind of like puzzle pieces.
But enzymes aren’t a perfect fit until the enzyme and the substrate tweak their shape
a little bit to fit really tightly together.
When they do, the enzyme-substrate combo is said to be in transition state which lets
it break the chemical bonds of that substrate, ultimately speeding up the reaction.
Afterwards, the substrate turns into the products and the enzyme can go on to catalyze more
reactions.
This general concept still holds to modern day — enzymes lower the activation energy
so the reaction happens faster.
No quantum chemistry needed, classic chemistry still applies.
Fast forward to 1966, researchers at the University of Pennsylvania saw a reaction that defied
classical models, so they explained it with quantum physics.
They observed a photosynthetic bacteria that uses light to oxidize a protein called cytochrome.
When it’s exposed to light, it photosynthesizes — the cytochrome donates an electron to
the molecules around it.
This reaction was shown to be temperature dependent.
Hotter conditions increased reaction speeds, colder temperatures slowed them down.
Adding an enzyme into the mix still increased reaction speed, but ultimately the whole thing
could be influenced by temperature.
Here’s where things get interesting, that reaction had been demonstrated even at extremely
low temperatures.
Like way below zero Celsius.
To figure out how this worked, they came up with a machine that would let them shine a
super fast, high energy laser at these bacteria and trigger their enzymes to make the reaction
happen.
They fired their laser at the bacteria and measured the reaction speed.
They found that as they dropped the temperature, the reaction speed dropped...until they hit
-173oc at which point the reaction speed hit a plateau and didn’t drop with temperature
anymore.
This plateau happened all the way down to -238oc.
So the reaction still had to climb over some kind of hill but according to classical mechanics,
the enzyme shouldn’t be able to lower the hill as much as they saw in those extremely
cold temperatures.
In their paper, they proposed that enzymes weren’t helping the reaction to “lower”
the hill, maybe they were burrowing through it.
This was the first experimental evidence that maybe quantum tunneling could explain this
temperature dependent biological phenomenon.
Now I’m not even going to pretend to be an expert on quantum tunneling, so I’m going
to hand it over to Jade from the youtube channel Up and Atom to let her explain it.
Take an every day classical scenario, like, trying to roll an object over a hill.
If the object isn’t given enough energy to get over the hill, it’ll simply roll
back down.
It doesn’t matter how many times you try, or for how long, if it doesn’t have enough
energy, it will never get over that hill.
Things are different in quantum land.
If a particle doesn’t have enough energy to jump a barrier, sometimes it can still
make it through to the other side.
This is because of a phenomenon called wave-particle duality.
See in the quantum realm, particles sometimes act sometimes like particles, but sometimes
like waves.
This wave represents the probability of them being in a particular place.
So instead of a particle traveling toward a barrier, imagine a wave of probability.
Now when this wave hits the barrier, unlike what a particle would do which is get 100%
rebounded, a tiny tiny fraction of the wave seeps through.
Now because this wave represents the probability of an electron being there, there is a tiny
tiny probability that the electron will end up being there.
So sometimes, even when a quantum particle doesn’t have enough energy to jump a barrier,
because of its dual wave like nature, we can find it on the other side.
The results of that experiment in the 60s offered an explanation for how electrons act
more like waves than particles, at least at extremely low temperatures.
Now, electrons are really tiny which makes them more likely to tunnel than bigger particles
like protons or neutrons.
But about a third of the enzymes out there work by facilitating the transfer of Hydrogen
atoms, which are mostly proton.
So the next challenge for quantum biologists was to figure out if Hydrogen can tunnel too.
In 1989, a team of researchers led by Judith Klinman out of Berkeley set out to prove that
this happens thanks to something called the kinetic isotope effect.
Atoms get their identity based on how many protons they have.
Hydrogen has one proton, carbon has six, neon has ten.
But atoms can have different numbers of neutrons in their nucleus, which we call isotopes of
that atom.
Hydrogen atoms usually have one neutron, but can come in isotopes where they have two or
three neutrons.
The interesting chemical properties of an element usually come from its electrons.
Changing its neutrons won’t change its reactivity much, but it will change how heavy it is and
how quickly it reacts, hence kinetic in kinetic isotope effect.
Assuming all other conditions stay the same, substituting a heavier isotope of hydrogen
ought to result in a slower reaction rate..
Classical mechanics can predict how much faster a light isotope will react than a heavier
isotope and give it a numerical value.
I’m not gonna confuse you with the calculations itself, but just know that it’s something
that can be predicted.
Klinman was interested in an enzyme called alcohol dehydrogenase, or ADH, which catalyzes
this reaction, a hydrogen atom is transferred from benzyl alcohol to benzaldehyde.
Replacing the lightest isotope,with the heavier isotopes should slow down the reaction.
But from a quantum perspective, as soon as you add another neutron onto that hydrogen
atom, the ability for it to tunnel drops significantly.
For Klinman, the heavier hydrogen isotopes should react much more slowly than predicted.
Sure enough, that’s exactly what her group observed.
Protium was catalyzed so much faster than its heavier isotopes that, according to this
research group, it had to be acting more like a wave than a particle and thus, it had to
be tunneling.
Now, this experiment was conducted at 25oc, about room temperature, which is kind of the
kicker here.
Life happens at warm temperatures from a quantum perspective.
The warmer the temperature, the less likely quantum mechanics has any effects.
It’s something called quantum decoherence.
So in follow up experiments published in 2004, Klinman and colleagues used the same enzyme
and reaction and found that above 30oc, the reaction behaved as predicted by classical
mechanics.
No quantum mechanics needed.
So At the sub zero temperatures where enzyme quantum tunneling is appreciable, it’s too
cold for life to thrive, so is any of this relevant.?
Well, sure, it’s relevant.
But instead of simply bestowing my blessing on the quantum biology model of enzymes, I
want to draw a more nuanced conclusion.
If we revisit Mary Schweitzer and the T rex collagen, we see an enzyme at work.
Collagenase catalyzed the separation of chemical bonds that had held strong for tens of millions
of years.
For the temperature and enzymes involved quantum decoherence probably prevented any involvement
from tunneling, so our dinosaur model probably doesn’t use quantum tunneling..
For the temperature and enzyme involved, quantum decoherence probably prevented any involvement
from tunneling, so our dinosaur example probably doesn’t involve quantum physics.
To give this model some credit, there are a lot of unanswered questions within the study
of enzymes.
And maybe these initial experiments are the thin end of the wedge and quantum biology
might help us answer them someday.
The books and papers that I read to research this video are obviously going to say that
quantum biology is the coolest thing ever, but hopefully this video shows that it’s
more complicated than that.
There is some evidence that some enzymes use quantum tunneling in some situations.
But that’s all we can say.
For now.
If you’re sitting there thinking “dang, this is dope, I want to learn more about this”
then go check out the video Jade and I made on her channel and while you’re there, make
sure to subscribe to her, she’s really good at making difficult topics understandable.
And thank you to my Patrons on Patreon.
I couldn’t do it without ya.
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Have fun, be good.
See you next time!