Life on the Edge: The Coming of Age of Quantum Biology

by Johnjoe McFadden

But the amount of energy supplied by the interaction of the earth’s magnetic field with the molecules within living cells is less than a billionth of the energy needed to break or make a chemical bond. How, then, can that magnetic field be perceptible to the robin?

For example, in describing the rules obeyed by electrons and how they arrange themselves within atoms, quantum mechanics underpins the whole of chemistry, material science and even electronics.

In fact, it has been estimated that over one-third of the gross domestic product of the developed world depends on applications that would simply not exist without our understanding of the mechanics of the quantum world.

Quantum mechanics was born when it was discovered in the early years of the twentieth century that subatomic particles can behave like waves; and light waves can behave like particles.

The German scientists Max Knoll and Ernst Ruska realized that, since the wavelength (the distance between successive peaks or troughs of any wave) associated with electrons was much shorter than the wavelength of visible light, a microscope based on electron imaging should be able to pick out much finer detail than an optical microscope.

So, in 1931, Knoll and Ruska built the world’s first electron microscope and used it to take the first ever pictures of viruses, for which Ernst Ruska was awarded the Nobel Prize, perhaps rather belatedly, in 1986 (two years before he died).

But particles that obey the rules of quantum mechanics, such as atomic nuclei, have a neat trick up their sleeve: they can easily pass through such barriers via a process called “quantum tunneling.” And it is essentially their wave–particle duality that enables them to do this.

If a nucleus has too many of one type or the other, then the rules of quantum mechanics dictate that the balance has to be redressed and those excess particles will change into the other form: protons will become neutrons, or neutrons protons, via a process called beta-decay.

The key point is that the deuteron owes its existence to its ability to exist in two states simultaneously, by virtue of quantum superposition. This is because the proton and neutron can stick together in two different ways that are distinguished by how they spin.

It was discovered back in the late 1930s that within the deuteron these two particles are not dancing together in either one or the other of these two states, but in both states at the same time—they are in a blur of waltz and jive simultaneously—and it is this that enables them to bind together.*4

This is important when considering that weird quantum property of spin, since paired electrons tend to spin in opposite directions, so their total spin cancels to zero.

The answer is that, down in the microscopic quantum world, particles can behave in these strange ways, like doing two things at once, being able to pass through walls, or possessing spooky connections, only when no one is looking. Once they are observed, or measured in some way, they lose their weirdness and behave like the classical objects that we see around us.

What we are talking about here is what happens when a water molecule bumps into one of a pair of entangled particles: its subsequent motion will be affected by the state of that particle, so that if you were to study the water molecule’s subsequent motion you could deduce some of the properties of the particle it had bumped into. So, in this sense, the water molecule has carried out a “measurement” because its motion provides a record of the state of the entangled pair, whether or not anyone is there to examine it. This kind of accidental measurement is usually sufficient to destroy entangled states.

Quantum phenomena such as superposition and tunneling have been detected in lots of biological phenomena, from the way plants capture sunlight to the way that all our cells make biomolecules. Even our sense of smell or the genes that we inherit from our parents may depend on the weird quantum world.

Moving objects were said to possess energy that could be transferred to stationary objects they bumped into, causing them to move. But forces could also be transmitted remotely between objects: examples of these were the gravitational force of the earth, which pulled Newton’s apple to the ground, or the magnetic forces that deflected compass needles.

By this time, it was known that other forms of energy, such as heat and light, were also capable of interacting with the constituents of matter, atoms and molecules, causing them to become hotter, emit light or change color.

Not only that, but the science is extraordinarily general, applicable not only to heat engines, but to nearly all the standard chemistry that takes place whenever we burn coal in air, allow an iron nail to rust, cook a meal, manufacture steel, dissolve salt in water, boil a kettle or send a rocket to the moon. All these chemical processes involve the exchange of heat and they are, at a molecular level, all driven by thermodynamic principles that are based on random motion.

In thermodynamics, the term entropy is used to describe a lack of order, and so highly ordered states are described as having low entropy.

However, in 1902 the American geneticist Walter Sutton noted that intracellular structures called chromosomes tended to follow the inheritance of Mendelian factors, leading him to propose that genes were located in chromosomes.

Then, in 1943, the Canadian scientist Oswald Avery managed to transfer a gene from one bacterial cell to another by extracting DNA from the donor cell and injecting it into the recipient cell. The experiment demonstrated that it was the DNA in the chromosomes that carried all the vital genetic information, not the proteins or other biochemicals.

Yet every living cell in your body is continually synthesizing thousands of distinct biochemicals within a reaction chamber filled with just a few millionths of a microliter of fluid.

How do all those diverse reactions proceed concurrently? And how is all this molecular action orchestrated within a microscopic cell? These questions are the focus of the new science of systems biology; but it is fair to say that the answers remain mysterious!

Life is different. No one has ever discovered a condition that favors the direction: dead cell → live cell.

We can mix biochemicals, we can heat them, we can irradiate them; we can even, like Mary Shelley’s Frankenstein, use electricity to animate them; but the only way we can make life is by injecting these biochemicals into already living cells, or by eating them, thereby making them part of our own bodies.

The conventional understanding at the time was that heat radiation traveled, like other forms of energy, through space as a wave. The problem was that the wave theory could not explain the way certain hot objects radiate energy. So Planck proposed the radical idea that the matter in the walls of these hot bodies vibrated at certain discrete frequencies, which had the consequence that the heat energy was only radiated in tiny discrete lumps, or “quanta,” that could not be subdivided. His simple theory was remarkably successful, but was a radical departure from the classical theory of radiation, in which energy was regarded as continuous. His theory suggested that energy, instead of flowing out of matter like water pouring continuously from a tap, came out as a collection of separate, indivisible packages—as if from a slowly dripping tap.

Albert Einstein extended this idea and suggested that all electromagnetic radiation, including light, is “quantized” rather than continuous, coming in discrete packets, or particles, which we now call photons. He proposed that this way of thinking about light could account for a long-standing puzzle known as the photoelectric effect, a phenomenon whereby light could knock electrons out of matter. It

Heisenberg argued not only that we could not say exactly where an atomic electron was if we weren’t measuring it, but that the electron itself did not have a definite location because it was spread out in a fuzzy, unknowable way.

Schrödinger preferred to think of it as a real physical wave when we aren’t looking at it, which “collapses”*9 to a discrete particle whenever we do look.

And here lies the profound difference between the two approaches, for in our Newtonian world the solution of an equation of motion is a number, or a set of numbers, that define(s) the precise location of an object at a given moment in time. In the quantum world, the solution of the Schrödinger equation is a mathematical quantity called the wave function, which does not tell us the precise location of, say, an electron at a particular moment in time, but instead provides a whole set of numbers that describe the likelihood of the electron’s being found at different locations in space if we were to look for it there.

the best we can do is work out a set of numbers that give the probability of finding it not at a single location, but at every point in space simultaneously.

Only through the act of looking (carrying out a measurement) can we “force” the electron to become a localized particle.

Pascual Jordan returned to Germany, to a post at the University of Rostock, from where over the next couple of years he maintained a correspondence with Bohr about the relationship between physics and biology. Their ideas culminated in what is arguably the first scientific paper on quantum biology, written by Jordan in 1932 for the German journal Die Naturwissenschaften and entitled “Die Quantenmechanik und die Grundprobleme der Biologie und Psychologie” (“Quantum mechanics and the fundamental problems of biology and psychology”).

Thermodynamics works like this: it is the average behavior of lots of molecules that is predictable, not the behavior of individual molecules.

all the laws of classical physics and chemistry—including the laws governing the dynamics of fluids or chemical reactions—are based on this “averaging of large numbers” or “order from disorder” principle.

Schrödinger went further than simply observing that the statistical laws of classical physics could not be relied on at the microscopic level: he quantified the decline in accuracy, calculating that the magnitude of deviations from those laws is inversely proportional to the square root of the number of particles involved.

For example, we saw how scattered spinning hydrogen nuclei in our body can be lined up to generate a coherent MRI signal from the quantum property of spin—but only by applying a very strong magnetic field provided by a big, powerful magnet, and only for as long as that magnetic force is maintained: as soon as the magnetic field is switched off, the particles become randomly aligned again by all the molecular jostling, and the quantum signal becomes scattered and undetectable.

Enzymes are the engines of life.

This molecular bumping and jostling can break the chemical bonds that hold the atoms together within molecules and even allow them to form new bonds. But the atoms of more stable molecules—those that are common in our environment—are held together by bonds strong enough to resist the surrounding molecular turbulence.

Even stable molecules can, however, be ripped apart if they are provided with sufficient energy. One possible source of that energy is more heat, which speeds up molecular motion. Heating up a chemical will eventually break its bonds.

But another way of converting reactants to products is to lower the energy barrier they need to climb over. This is what catalysts do.

What is the enzyme doing? The answer is pretty obvious: enzymes manipulate individual atoms, protons and electrons, within and between molecules.

So the key events of respiration actually have very little to do with the process of breathing, but consist instead of an orderly transfer of electrons through a relay of respiratory enzymes inside our cells.

An important feature of quantum mechanics is that the lighter the particle, the easier it is for it to tunnel. It is not surprising, therefore, that once this process was understood to be a ubiquitous feature of the subatomic world it was the tunneling of electrons that was found to be most common as they are very light elementary particles.

For a particle to quantum tunnel, it must remain wavy in order to seep through the barrier. This is why big objects, such as footballs, do not quantum tunnel: they are made up of trillions of atoms that cannot behave in a coordinated coherent wave-like fashion.

Even a single proton is two thousand times as heavy as an electron, and quantum tunneling is known to be exquisitely sensitive to how massive the tunneling particle is: small particles tunnel readily whereas heavy particles are far more resistant to tunneling unless the distances to be covered are very short.

Remember that living cells are extraordinarily crowded places, crammed with complex molecules in a state of constant agitation and turbulence, similar to that billiard-ball-like molecular motion we explored in the last chapter that is responsible for driving steam trains up hillsides. If you remember, it is this kind of random motion that scatters and disrupts the delicate quantum coherence and makes our everyday world appear “normal” to us.

Quantum coherence would not be expected to survive within this molecular turbulence, so the discovery that quantum effects, such as tunneling, manage to persist in the sea of molecular agitation that is a living cell is very surprising.

Elsewhere, all the biomolecules of life—fats, DNA, amino acids, proteins, sugars—are being made and unmade by different enzymes.

Not so for the atom; in the absence of any measurement, the atom really is everywhere.

It is important to remember that this reinforcement and cancellation process—quantum interference—takes place even when only a single particle is involved.