Quantum tunneling is where an electron hops from one biomolecule to the next; violating classical laws of physics. Here are a few interesting snippets from Mark Anderson's DISCOVER article Is Quantum Mechanics Controlling Your Brain.
Quantum tunneling and smell:
What is really happening, Turin posited, is that the approximately 350 types of human smell receptors perform an act of quantum tunneling when a new odorant enters the nostril and reaches the olfactory nerve. After the odorant attaches to one of the nerve’s receptors, electrons from that receptor tunnel through the odorant, jiggling it back and forth. In this view, the odorant’s unique pattern of vibration is what makes a rose smell rosy and a wet dog smell wet-doggy.
Quantum tunneling and green tea:
Even green tea may tie into subtle subatomic processes. In 2007 four biochemists from the Autonomous University of Barcelona announced that the secret to green tea’s effectiveness as an anti-oxidant—a substance that neutralizes the harmful free radicals that can damage cells—may also be quantum mechanical...Free radical molecules, by-products of the body’s breakdown of food or environmental toxins, have a spare electron. That extra electron makes free radicals reactive, and hence dangerous as they travel through the bloodstream. But an electron from the catechin can make use of quantum mechanics to tunnel across the gap to the free radical. Suddenly the catechin has chemically bound up the free radical, preventing it from interacting with and damaging cells in the body.
Quantum tunneling and consciousness:
Hameroff speculates that anesthetics “interrupt a delicate quantum process” within the neurons of the brain. Each neuron contains hundreds of long, cylindrical protein structures, called microtubules, that serve as scaffolding. Anesthetics, Hameroff says, dissolve inside tiny oily regions of the microtubules, affecting how some electrons inside these regions behave.
He speculates that the action unfolds like this: When certain key electrons are in one “place,” call it to the “left,” part of the microtubule is squashed; when the electrons fall to the “right,” the section is elongated. But the laws of quantum mechanics allow for electrons to be both “left” and “right” at the same time, and thus for the microtubules to be both elongated and squashed at once. Each section of the constantly shifting system has an impact on other sections, potentially via quantum entanglement, leading to a dynamic quantum-mechanical dance.
It is in this faster-than-light subatomic communication, Hameroff says, that consciousness is born.
Link to article here.