Science is perception: what can our sense of smell tell us about ourselves and the world around us?

Abstract

Human sensory processes are well understood: hearing, seeing, perhaps even tasting and touch—but we do not understand smell—the elusive sense. That is, for the others we know what stimuli causes what response, and why and how. These fundamental questions are not answered within the sphere of smell science; we do not know what it is about a molecule that … smells. I report, here, the status quo theories for olfaction, highlighting what we do not know, and explaining why dismissing the perception of the input as ‘too subjective’ acts as a roadblock not conducive to scientific inquiry. I outline the current and new theory that conjectures a mechanism for signal transduction based on quantum mechanical phenomena, dubbed the ‘swipe card’, which is perhaps controversial but feasible. I show that such lines of thinking may answer some questions, or at least pose the right questions. Most importantly, I draw links and comparisons as to how better understanding of how small (10’s of atoms) molecules can interact so specially with large (10 000’s of atoms) proteins in a way that is so integral to healthy living. Repercussions of this work are not just important in understanding a basic scientific tool used by us all, but often taken for granted, it is also a step closer to understanding generic mechanisms between drug and receptor, for example.

Implausibility of the vibrational theory of olfaction

“…Turin's idea that electron transfer occurs at ORs and that these ORs can detect odorant vibrational frequencies has gained traction in recent years (37,(43)(44)(45)(46)(47). These theoretical works (37,43,47) are in support of the vibration theory but remain largely tentative because they admittedly rely on unconfirmed assumptions, lacking experimental evidence, to make the proposal appear to be feasible.…”

“…Insofar as the ability to distinguish odors of isotopomers directly tests the predictions of the vibration theory, the comparative response of human and mouse ORs to isotopomers of these selected ligands in the heterologous OR expression system constitutes a robust test of the vibration theory. Finally, we discuss the basis for recent vibration theories of olfaction and supporting computational evidence (37,(43)(44)(45)(46)(47) in light of well-established electron transfer theories (48). We point out that key assumptions underlying the vibration theory lack experimental support and are missing important physical features expected for biological systems.…”

Multiphonon processes of the inelastic electron transfer in olfaction

“…Our sense of smell (olfaction) is of importance to make judgement about the surrounding environment and influence our perceptions. Although the processes of olfactory recognition have been extensively studied both in experimental 1–11 and theoretical 5,6,11–15 aspects during the past several decades, the fundamental mechanism of olfaction is still hotly debated. To date, two mainstream mechanisms have been proposed: one is the docking model (the lock-and-key model), in which the odorant size, shape and functional groups determine the activation of olfactory receptors; the other one is the vibrational model, in which the special vibrational frequencies of odorant compounds contribute to odorant recognition.…”

Inelastic electron transfer in olfaction: multiphonons processes

“…Our sense of smell (olfaction) is of important to make judgement about surrounding environment and influence our perceptions. In spit of the processes of olfactory recognition have been extensively studied both in experimental [1][2][3][4][5][6][7] and theoretical [2,3,[7][8][9][10][11] aspects during the past several decades, the fundamental mechanism of olfaction is still hot debated. Until now, two mainstream mechanisms have been proposed: one is the docking model (lock-and-key model), in which the odorant size, shape and functional groups determine activation of olfactory receptors; another is the vibrational model, in which the special vibrational frequencies of odorant compounds contribute to odorant recognition.…”