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

by Johnjoe McFadden

Notably, it seemed to have been found inside neurons within the upper beaks of the most famous of avian navigators, homing pigeons,9 suggesting that their neurons were responding to magnetic signals picked up by the magnetite crystals and then sending a signal to the animal’s brain.

More recent research showed that pigeons became disorientated and lost their ability to track the geomagnetic field when small magnets were attached to their upper beaks, where those magnetite-filled neurons were apparently located.10

This angle of inclination (hence the name for this kind of compass) is near-vertical (pointing into the ground) close to the poles, but parallel to the ground at the equator.

And because this is the quantum world, an electron can, when not being watched, spin in both directions at the same time.

In fact, electrons are not only not tiny spheres, they cannot even be said to have a size at all.

We can then think of their spins as canceling out, and we refer to them as being in a spin singlet state, since they can only inhabit a single state.

However, when not paired together at the same energy level, two electrons can spin in the same direction, and this is called a spin triplet state,*2 as in the reaction that Schulten studied.

However, although such “instantaneous action at a distance” (as it is often described) is not found in our everyday classical world, it is a key feature of the quantum domain. Its technical name is nonlocality, or entanglement, and it refers to the idea that something happening “over here” can have an instantaneous effect “over there” no matter how far away “there” is.

So although both electrons are in a superposition of being both up and down at the same time, in a peculiar quantum way they must, at all times, have opposite spin.

Now let’s separate the two entangled electrons so that they are no longer in the same atom. If we then decide to measure the spin state of one electron we will force it to choose which way it is spinning.

Say we find that, after measurement, it is spin-up. Because the electrons were in an entangled singlet spin state, this means that the...

But remember that, before measurement, both were in a superposition of spinning up and down. After measurement both have distinct states: one of them is up and the other is down. So the second electron has instantly and remotely changed its physical state from being in a superposition of spinning both ways at once to being spin-down—without being touched. All we have done is to measure the state of its partner. And in principle it doesn’t matter how far away this second electron is—it could be on the other side of the universe and the effect would...

Quantum entanglement is different. Before the measurement, neither electron has a definite spin direction. It is only the act of measurement (of either entangled particle) that forces both electrons to change their state from each being in a quantum superposition of both up and down to being in a definite state of up or down;

Not only does quantum measurement of one electron force it to “choose” to spin either up or down; that “choice” instantaneously forces its twin to adopt the complementary state, no matter how far away it is.

But this is the quantum world, and just because the electron that jumped out of the atom can now flip its spin, this doesn’t mean that it definitely has. Each of the two electrons will still be in a superposition of spinning both ways at once, and as such the pair will exist in a superposition of being in a singlet and a triplet state simultaneously: spinning in the same direction and in opposite directions at the same time!

The moral is that tiny energies can have significant effects, but only if the system on which they operate is very finely balanced between two different outcomes.

So, to detect the impact of the earth’s very weak magnetic field we need the chemical equivalent of a granite block in a finely balanced state, such that it could be dramatically affected by the slightest of external influences, such as a weak magnetic field.

And now we come back to Klaus Schulten’s fast triplet reaction. You may recall that electronic bonds between atoms are often formed by the sharing of a pair of electrons. This electron pair is always entangled and almost always in a singlet spin state: that is, the electrons have opposite spin. However, remarkably, the two electrons can remain entangled even after the bond between the atoms is broken. The separated atoms, which are now called free radicals, can drift apart, and it becomes possible for the spin of one of the electrons to flip over so that the entang...

An important feature of this quantum superposition is that it isn’t necessarily equally balanced: the probabilities of our catching the entangled pair of electrons i...

And, crucially, the balance between these two probabilities is sensitive to any external magnetic field. In fact, the angle of the magnetic field with respect to the orientation of the separated pair strongly influences t...

Crucially, cryptochrome was known to be the kind of protein capable of forming free radicals during its interaction with light.

So a conventional compass may be disrupted by magnetic fields oscillating at low frequencies but not at high frequencies.

This intriguing result24 also shows that, if it exists, the entangled pair must be able to survive in the face of decoherence for at least a microsecond (a millionth of a second), because otherwise its lifetime would be too short to experience the ups and downs of the applied oscillating magnetic field.

But in 2011, a paper from Vlatko Vedral’s laboratory in Oxford presented quantum theoretical calculations of the proposed radical pair compass and demonstrated that superposition and entanglement should be sustained for at least tens of microseconds, greatly exceeding the durations achieved in many comparable manmade molecular systems; and potentially long enough to tell a robin which way it needs to fly.

Kapitsa’s proposal was eventually confirmed by satellite measurements of the area in 1996, which revealed a subglacial lake up to 500 meters deep (from the top of its liquid surface to its bottom) and the size of Lake Ontario. The team named it Lake Vostok.

Thermal currents drive the water in the lake so that just beneath its icy ceiling it is going through a continual cycle of freezing and thawing. This process has continued ever since the lake was sealed off, so its roof is made up not of glacier ice, but of frozen lake water—known as accretion ice—that extends to tens of meters above the liquid surface of the lake.

Many biologists would argue, indeed, that self-replication is life’s defining feature. But living organisms could not replicate themselves unless they were capable of first replicating the instructions for making themselves.

The rate of copying errors in DNA replication, what we call mutations, is usually less than one in a billion.

High-fidelity copying is crucial for life because the extraordinary complexity of living tissue requires an equally complex instruction set, in which a single error may be fatal.

Schrödinger proposed that genes were what he called aperiodic crystals: that is, crystals with a similar repeated molecular structure to standard crystals, but modulated in some way, for example with different intervals or periods (hence “aperiodic”) between the repeats or different structures in the repeats—more like complex tapestry than wallpaper.

Base A has to pair with base T because each A holds protons at precisely the right positions to form hydrogen bonds with a T. An A base cannot pair with a C base because the protons would not sit in the right places to make the bonds.

Schrödinger predicted, life works via order that goes all the way down from the structure and behavior of whole organisms to the position of protons along its DNA strands—order from order—and it is this order that is responsible for the fidelity of heredity.

For evolution to be successful, natural selection needs a source of variation on which to cut its teeth.

A key component of the neo-Darwinian synthesis is the principle that mutations occur randomly; variation is not generated in response to an environmental change.

So when the environment changes, a species has to wait for the right mutation to come along—through random processes—in order to track that change.

Luria and Delbrück set out to discover whether bacterial mutants able to resist viral infection already existed in the population, as predicted by neo-Darwinism, or arose only in response to an environmental challenge by a virus, as predicted by Lamarckism.

So, was Schrödinger right? Are mutations a kind of quantum jump?

But isn’t a proton a particle? Why, then, is it drawn as a dotted line rather than a single dot? The reason is, of course, that protons are quantum entities that have both particle and wave character: so the proton is delocalized, behaving like a smeared-out entity or a wave that sloshes between the two bases.

Each of the DNA bases can therefore exist both in its common canonical form, as seen in Watson and Crick’s double helix structure, and in the rarer tautomer, with its coding protons shifted across to new positions.

But remember that the protons forming the hydrogen bonds in DNA are responsible for the specificity of base-pairing that is used to replicate the genetic code. So, if the pair of coding protons move (in opposite directions), they are effectively rewriting the genetic code. For example, if a genetic letter in a DNA strand is a T (thymine) then in its normal form it pairs, correctly, with A. However, if a double proton swap occurs then both T and A will adopt their tautomeric forms.

Of course, the protons may jump back again but if they happen to be in their rare tautomeric forms*6 at the time the DNA strand is being copied then the wrong bases ...

The tautomeric T can pair with G, rather than A, so G will be incorporated into the new strand where there was an A in the old strand. Similarly, if A is in its tautomeric state when the DNA is being replicated then it will pair with C, rather than T, so the new strand has C, where the old strand had T (figure 7.3). In either case, the newly formed DN...

Classical information can be read and reread over and over again without changing its message, whereas quantum systems are always perturbed by measurement. So when the DNA polymerase enzyme scans a DNA base to determine the position of coding protons, it is carrying out a quantum measurement, no different in principle from when a physicist measures the position of a proton in the laboratory.

A key characteristic of this process is that some genes are read much more often than others. If reading the DNA code during transcription constitutes a quantum measurement, then the more frequently read genes would be expected to be subject to more measurement-induced perturbations, leading to higher rates of mutation.

recent study of human genes concluded that those of our genes that are read at the highest levels tend to be mutated the most.

The reading of the DNA involves biochemical reactions that may disturb or damage the molecular structure of genes in many different ways, causing mutations, without any recourse to quantum mechanics.

Instead of looking for mutations that conferred resistance to a deadly virus, he instead starved the cells and looked for mutations that would allow bacteria to survive and grow. Like Luria and Delbrück, he saw that a few mutants managed to grow straight away, showing that they were preexisting in the population; but, in contrast to the earlier study, he observed many more mutants appearing much later, apparently in response to starvation.

The findings appeared to support the discredited Lamarckian theory of evolution—the starved bacteria weren’t growing long necks but, just like Lamarck’s imaginary antelope, they appeared to be responding to an environmental challenge by generating heritable modifications: mutations.

There was simply no known mechanism that would allow a bacterium, or indeed any creature, to choose which genes to mutate and when.

The finding also appeared to contradict what is sometimes called the central dogma of molecular biology: the principle that information flows only one way during transcription, from DNA out to proteins to the environment of a cell or organism.