Quantum Biology: Bridging the Gap Between Quantum Mechanics and Biology

Siya Jatia | SQ Online (2024-2025)

Saltman QuarterlyStudent
··8 min read

“What is Life?”

This title refers to 1944’s bestseller book, not the latest “10 Ways to Avoid an Existential Crisis” from Cosmopolitan, as the name would suggest. This book was written by Erwin Schrödinger as a layman’s guide to the physics in living cells—the same Schrödinger whose cat is both dead and alive at the same time! This book was one of the first of its kind to bridge the worlds of biology and physics to look at biological functioning through a new lens. Schrödinger proposes an initial version of the field that goes on to become ‘Quantum Biology,’ discussing how quantum mechanics may influence the organization of living organisms. He nudges people to accept an uncomfortable thought: “things (even biological things!) can be in two places at the exact same time.”

Coming to the preliminary question at hand: why did physicists venture into biology, and what exactly is quantum biology? It is an intersection of quantum mechanics and biology which utilizes the fundamental concepts of quantum physics to understand molecular biology, chemistry, and neuroscience from a new and revised interdisciplinary perspective. As a result, the field allows for exploration of phenomena where classical physics, or a singular plausible explanation, doesn’t do full justice in explaining biological functions. Owing to the lack of experimental viability, the field has seen slow progress. However, with a growing number of concrete findings, the field has developed to where it stands today—at the brink of breakthroughs in medicine and healthcare. This includes specific drug design through understanding enzymatic activity, precision quantum sensor imaging for increased accuracy in diagnostics, sustainable agriculture, and so much more! What is specifically interesting is the possibility of generating artificial renewable energy through mimicking the process of plant photosynthesis, offering a promising solution to the global energy crisis.

Quantum Mechanics for Biologists

Quantum mechanics is a fundamental theory devised to explain the structure and arrangement of molecules, with a focus on subatomic particles such as protons, electrons, and neutrons. Quantum mechanics accounts for minute timeframes, operating on the nanometer and sub-nanometer scales. Unlike the importance of determinism and predictability in classical physics, quantum physics emphasizes uncertainty and probability. At the quantum level, particles follow superposition, or the idea that they can simultaneously exist in multiple states (positions) at any point in time. Having said that, it doesn’t mean that the position cannot be defined – it just acknowledges the presence of alternate positions. Think of a coin toss! Once the coin is spinning in the air, just before it lands, it’s not just either heads or tails—it’s both. Until the coin lands and you observe the result, it doesn’t take a specific position. For example, if heads has been observed, superposition would suggest that the coin could be tails at this exact moment in time. Hence, at the simplest level, it says that there could be alternate versions of the observed reality. Due to this uncertainty, different properties like position and momentum cannot be precisely evaluated simultaneously.

Quantum mechanics proposes wave-particle duality, which states that all particles adopt both wave-like (such as interference and diffraction) and particle-like (such as being localized in position) properties. This wave-like pattern allows for the particle to exhibit what is known as quantum coherence when interacting with one another. Coherence is the property that creates synchronization in the way particles interact, reflecting their multiple potential states, thereby maintaining superposition. This indicates that particles are in a combination of states at all times, instead of a single, definite state and properties like position or momentum of one particle are inevitably influenced by and correlated with the other particle. Quantum mechanics says that this relationship is not random, but can be deduced based on their shared quantum state. In quantum biology, researchers have historically used coherence as a starting point to understanding efficient energy transfers and information processing in biological processes such as photosynthesis in plants.

Photosynthesis: Current Research and Future Directions

Photosynthesis, in its simplest form, is the process of using carbon dioxide and water to make glucose and oxygen, providing plants with their own nutrition. The process converts light energy, absorbed by the green pigment chlorophyll, into chemical energy stored in glucose. This energy is further used for metabolic processes within the plant.

Now, to look at photosynthesis more in-depth, pigment protein complexes (PPCs) and energy transfer mechanisms are vital in maximizing energy output. Chloroplasts, present in the mesophyll cells of plant leaves, are specialized organelles containing chlorophyll. When multiple chlorophyll molecules are organized in such a way that it maximizes the photoabsorption, it is referred to as the chlorophyll antenna. A PPC, as the name suggests, is a complex structure of pigments bound to proteins. PPCs play a crucial role in photosynthesis: capturing and transferring solar energy in the form of photons. One of the most studied PPCs is the Fenna-Matthews-Olson (FMO) protein complex, which is commonly found in green sulfur bacteria.

The FMO complex is a trimeric protein (made of three individual protein subunits) with each subunit consisting of eight specifically arranged bacteriochlorophyll molecules, or a bacterial equivalent of chlorophyll. The FMO complex acts as an intermediary—transferring energy as excitons, formed when electrons absorb energy, from the light-harvesting antenna complex to the reaction center, the “engine” of photosynthesis. The reaction center converts light energy into a flow of electrons, producing energy-rich molecules, like ATP and NADPH, which are then further utilized by the plant.

One hypothesis for this energy transfer is the process of Förster Resonance Energy Transfer (FRET). FRET bases the transfer on dipole-dipole interactions between molecular sites (such as pigments), which then causes hopping of energy between short distances. The bacteriochlorophylls act as stepping stones as they absorb energy and transfer it adjacently. Efficiency is important to maximize the yield of each cycle, especially for surviving in the competitive low-light conditions these green sulfur bacteria live in.

Understanding quantum coherence in the FMO complex can help explain the process by which the plant “decides” the most efficient method of energy transfer – by “considering” multiple alternate pathways simultaneously. Emphasis is placed on efficient pathways for energy transfer to ensure fast conversion of light energy to chemical energy in order to prevent the chances of the plant misallocating the light energy source for purposes other than to generate electron potentials. Losing light energy to other mechanisms would decrease the yield of photosynthesis, thereby nullifying the benefit of the efficient energy transfer mechanisms. By the principle of coherence, multiple different pathways for energy transfer can be explored – the system continually refining its selection to pursue the most efficient route.

Despite extensive research on the FRET hypothesis in FMO proteins, scientists have found practical evidence to question its validity using femtosecond multidimensional spectroscopy (FMS). This technique uses short laser pulses to study extremely rapid processes, such as energy transfer in femtoseconds (10-15 seconds), thus allowing scientists to track the movement of energy and electrons through time and space. Previous studies, using an earlier form of FMS called 2D spectroscopy, provided evidence for long-lived quantum coherence (a phenomenon where quantum states of coherence remain in sync over time). The studies concluded that this coherence could last up to 1.5 picoseconds (10-12 seconds), yet this time frame did not do justice to the rapid transfer that was theoretically predicted. The study by Duan Et al. found that the loss of quantum coherence between the molecules occurs in about 60 femtoseconds, significantly shorter than 1.5 picoseconds initially proposed. This implies that coherence between different exciton states is lost before it can significantly influence energy transfer. Thus, the study concluded that at physiological temperatures energy transfer dynamics are not significantly affected by inter-exciton coherences as they dissipate too quickly to have a meaningful impact.

A wave of such studies expanded on these findings, casting doubt on the theory of long-lived quantum coherence playing a critical role in photosynthetic energy transfer. Instead, these new studies have opened up possibilities for more refined mechanisms of quantum physics to describe PPC energy transfer. One such example is quantum tunneling, which explains how the wave-like properties of particles can allow them to pass through unsurpassable energy barriers. While in classical physics particles must meet an energy threshold to overcome the barrier, in quantum physics the particle’s wave properties may potentially allow it to virtually disappear at one side, and appear at the other—seemingly crossing it. Preliminary research suggests quantum tunneling could explain the high efficiency of bacteriochlorophylls’ ‘hopping’ mechanism because this explains energy transfer in non-linear conditions which require crossing energy barriers.

Conclusion

At this juncture in quantum biology, multiple possibilities are on the cusp of revolutionary breakthroughs. Future research welcomes alternative explanations and brings hope of real-world applications, such as energy harvesting and renewable energy through artificial photosynthesis. Research into quantum biology stretches into other biological topics, including quantum tunneling to explain the high efficiency of enzyme-catalyzed reactions and certain DNA mutations, quantum entanglement for birds to navigate Earth’s magnetic field using an eye protein called cryptochrome, and so much more. All in all, if this article leaves you bewildered, exasperated, and on the verge of pulling out your hair, you’re precisely where you should be. As Richard Feynman, a paragon of insight in the realm of quantum mechanics, insightfully said, “If you think you understand quantum mechanics, you don’t understand quantum mechanics.”

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