Quantum Biology: The Weird and the New
In 1944, the theoretical physicist, Erwin Schrödinger published a book, What is Life?, in which he explored how biology may be subject to quantum effects. In the book Schrödinger introduced the idea of an “aperiodic crystal”, which contained genetic information in the form of covalent bonds, an idea that stimulated Crick and Watson to explore the structure of deoxyribonucleic acid (DNA) in cells. What is fascinating about Schrödinger ‘s ideas is that he understood the importance of quantum mechanics on chemical and biological systems, in what he referred to as “order-from-disorder”. Indeed it was Schrodinger who coined the term “quantum biology” and it was he who was the first scientist to properly understand the importance and potential of the synthesis of quantum physics and modern biology.
Quantum biology, which explores the quantum effects on biological systems, marks a significant difference in how we relate to and understand biological processes, which have to-date been viewed in a very mechanistic, Newtonian, macroscopic manner. More precisely, quantum biology can be defined as the application of quantum mechanics to biological objects and problems. Two key concepts are central to understanding quantum biology – entanglement and superposition. Entanglement refers to objects that have no physical contact being able to influence each other, via a bizarre quantum connection. Superposition is difficult to define outside of a mathematical treatment, but a very simple, if inadequate explanation is that it is a quantum principle in which owing to a concept known as superposition of states, sub-atomic particles can be in two places at once. It is based on the overlapping of waves based on wave –particle duality.
Experiments have demonstrated this weird effect with photons reinforcing the counterintuitive predictions of quantum entanglement. As a concept, superposition was made famous through the Schrodinger’s cat analogy in which the concept of superposition was explained. In essence, superposition refers to the bizarre idea that particles can be in any possible state i.e., particles are in all possible states simultaneously and only by someone physically looking and measuring it does an object limit itself to a single possibility.
Now, with the emergence of this new, albeit somewhat speculative new science, many biological phenomena, including the most fundamental of all – the abiogenesis question, the process of how life arose or emerged from non-living matter, are being revisited and re-evaluated from a quantum perspective.
There is little doubt that quantum mechanics has had a revolutionary impact on modern science and technology and explains the basis of all modern electronics and digital technology as well as organic chemistry. Quantum mechanics is a branch of physics that looks at phenomena on the nanoscopic scale and explores the interactions between energy and matter based on the wave-particle duality, i.e. that every elementary particle exhibits properties of not only particles, but also waves. What is interesting about quantum biological effects is that they seem to be able to occur at ambient temperatures, whereas most quantum effects have only been observed when systems are cooled to very low temperatures.
Examples of quantum biology
One of the most interesting and researched areas of biophysics that involves quantum effects is the light dependent stage of photosynthesis. Superposition has been demonstrated in the process of energy transduction in the leaf. Photosynthesis involves using complex pigment molecules called chromophores, which help convert light energy (in the form of quanta) into chemical energy that can be used for the synthesis of basic sugars. Photosynthesis involves two fundamental parts: a light dependent stage and a light independent stage. The light dependent stage requires light to hit pigment molecules, such as chlorophyll a. This molecule is interesting because it has a high number of conjugated bonds i.e. alternating double and single carbon bonds. In a molecular orbital sense, a conjugated system is a system of connected p-orbitals, with delocalised electrons, which means the electrons are “shared” and not confined to one covalent bond. This property allows the pigment to be more stable as delocalisation of -electrons being linked to the lowering of potential energy of a species.
When light, in the form of quanta of energy (photons) hits the delocalised chlorophyll molecule, the absorption leads to electronic excitation (also referred to as an exciton) in which energy is transferred from one molecule to another until the excitation energy reaches a key point within the photosystem called the reaction centre.
It was originally thought that the movement of energy through the photosystem from the antenna complex through to the reaction centre was random, but recent research has demonstrated superposition. The movement of energy to the reaction centre via resonance energy transfer and molecular vibrations is not random, but rather it goes simultaneously along many different paths at once, and collapses at those wavelengths that are not efficient. This process makes photosynthesis extremely efficient and is being eagerly researched to try and exploit the same efficiency to enhance solar and other light harvesting devices. A new area of research has emerged that aims to engineer photosynthetic light capture from green algae in order to improve the capture of solar energy and store in a form of bio-fuel (biomass conversion).
Other areas in which quantum effects are inferred in biological processes include:
· DNA mutation - quantum tunnelling
· Bird migration
· Our sense of smell
· Many biochemical/enzymatic reactions
It was Schrödinger, who in his book, What is Life?, speculated that mutations might involve some form of quantum effect. Tautomeric (isomeric, where the relevant molecules are in equilibrium with one another) forms of DNA bases that have different proton positions may be a driver of mutation through a process known as quantum tunnelling, in which a particle moves through a barrier even though it does not appear to have enough energy to do so. In quantum tunnelling, a proton in a hydrogen bond could tunnel through the energy barrier of a hydrogen bond in a DNA base pair, which would produce a tautomeric bond. Numerous tautomers would have different pairing patterns, resulting in a form of mutation. What is clear, however, is that if quantum tunnelling is involved in mutation, it is one of many factors that may produce a mutation. It is however, quite fascinating to consider that mutation, which is the basis of genetic variation upon which natural selection acts could be caused by quantum effects such as tunnelling. Quantum tunnelling may also be involved in the catalytic action of some enzymes, whereby the rate of a particular reaction is increased many million fold over the uncatalysed rate.
In their book, Life on the Edge, Jim Al-Khalili and Johnjoe McFadden, provide an in-depth and fascinating account of the coming age of quantum biology. The authors explain how quantum biology helps explain bird migration and our sense of smell. Traditionally, biochemists had tried to understand smell and odour detection in term of a lock and key mechanism. The more complex vibration theory of smell, as advanced by scientists such Malcolm Dyson as early as the 1920s was less readily accepted, only being revived following experiments in 1996 and 2006, respectively, which demonstrated a strong theoretical base for a vibrational theory for smell, but more importantly, one based on inelastic electron tunnelling.
So what is the future for quantum biology? As already emphasised, this emerging field of science is still largely speculative and suffers from the fact that physicists do not always make great biologists and biologists rarely make good physicists. But as in many areas of biology and material science, with increased co-operation and an increase in biophysical research posts the potential gain from understanding quantum effects in biology is significant, especially in our understanding of energy transduction in the context of environmental sustainability. But outside the benefits, quantum biology may offer explanations for phenomena that biologists have struggled to previously comprehend. The problem with quantum mechanics is that it is inherently counterintuitive, especially to macroscopic biologists – but there is the challenge, and the rewards could be huge.
Co-Head of Science
David Game College, 2015