What are the quantum effects in living organisms
Quantum physics governs the very small world and the very cold world.
Your dog can't tunnel through a fence via quantum tunneling, and you won't see your cat exhibit wave-like properties. But the interesting thing about physics is that it keeps surprising us, quantum physics is starting to appear in unexpected places; in fact, it is working in animals, plants and our own bodies.
We used to think that biological systems were too hot, too wet, too chaotic for quantum physics to play any role in what they do. But now it seems that life uses quantum mechanical properties in chaotic real-world systems every day: including quantum tunneling, wave-particle duality, and even entanglement.
To understand how this all works, we can start by looking right up our own noses.
The human nose can distinguish over a trillion smells. But how does the sense of smell actually work? That remains a mystery.
When a molecule known as an odorant enters our nose, it can bind to receptors. Initially, the prevailing theory was that these receptors use the shape of the odorant to distinguish between odors. The so-called lock and key model suggested that when an odorant found a suitable receptor, it would bind to the receptor and trigger a specific odor. But when tested, the lock-and-key model ran into trouble: subjects were able to distinguish between the two odors even though the odor molecules were identical in shape.
There must be some other process at work.
Another still controversial model suggests that our noses are sensitive to vibrations within odor molecules. These vibrations occur when the individual atoms within the molecule swing back and forth from each other, as if they were mounted on small springs. When an odorant enters a receptor, the energy of its vibrations causes electrons to travel to another location in the receptor in the form of quantum tunneling.
The shape and vibration models can be combined. In the "swipe card model", our nose is sensitive to both the shape and vibration of the odorant.
A new model, the "luminescence hypothesis", proposes another conjecture: once an electron enters a new location in the receptor through tunneling, it loses energy. The hypothesis suggests that during this process, the electron emits photons; our nose detects these photons and then distinguishes the odor. Interestingly, the authors of this hypothesis suggest that it may help explain why some people with neocoron can lose their sense of smell.
Quantum mechanics may also play a role in evolution.
DNA has four bases, called A (adenine), C (cytosine), G (guanine) and T (thymine). These bases are "shaped" so that A always binds to T and G binds to C. During replication, an enzyme "unpacks" the DNA strand from top to bottom; the two sides of this unpacked DNA can now be built into the same DNA strand, matching A and C and G and T.
The bases are held together by hydrogen bonds, in which the hydrogen atoms attract negatively charged molecules - a bit like a magnet. Instead of sharing electrons, these bonds stick together electrostatically. When DNA is unbonded, occasionally the hydrogen nuclei (protons) can reach the other side of the unbonded DNA through quantum tunneling. When this happens, it creates a tautomer. A tautomer is another version of a molecule with the same chemical formula but a different shape, and therefore different connectivity.
A tautomer that survives long enough during replication can lead to mispaired base pairings with each other. Initially, it was thought that isoforms did not survive long enough to survive the entire replication process. Recently, however, scientists have discovered that they can survive through DNA replication and cause mutations; over time, this may affect the course of evolution.
Plants and bacteria that use photosynthesis take advantage of the quantum properties of light, using quantum coherence to convert sunlight into energy.
When sunlight hits a plant, chlorophyll molecules within the leaf absorb photons of a specific color, and these photons excite an electron within the chlorophyll. This energy is then transferred from the chlorophyll molecule to a structure called the "reaction center" where it is converted into chemical energy and stored for use by the plant.
But the path from chlorophyll to the reaction center is not straightforward or easy to find. The energy must reach its destination quickly, or it will be lost as heat. To alleviate this challenge, plants use an ingenious trick called quantum coherence.
Instead of taking one path and hoping that is the way to the reaction center, the electron uses its wave-like nature, taking all available paths at once, to find the reaction center each time. Quantum coherence is closely related to quantum entanglement, which has also been shown to bring efficiency gains to plants.
Reference links:
[1] https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0055780
[2]https://www.nih.gov/news-events/nih-research-matters/humans-can-identify-more-1-trillion-smells
[3]https://bigthink.com/life/quantum-physics-biology/
