![]() ![]() of the electronic states and/or nuclear states). The transit can be treated classically, or with various degrees of quantum definition (e.g. In all cases discussed here, transfer occurs between an initial (donor, D) and final (acceptor, A) state, and always within a protein environment that may be in a complex with a small molecule be it a substrate, odorant or chromophore. Where the rate describes a transition from D (donor, initial state or reactant) to A (acceptor, final state or product), where ρ is the density of states that can accept the transferring particle (or Franck–Condon (FC) factors), ℏ is the Planck constant (quantum of action) and H DA are Hamiltonian transition matrix, where the transition may be tunnelling. Whether any quantum theorizing illuminates and explains a biological effect is then briefly discussed in the conclusions with a final mention of the role of the environment and what remains as future work and challenges in the field. Where available, this review is written around experimental evidence and theory is described in order to explain/predict the quantum effects, depicted when possible in the figures. Fourthly, magnetoreception is briefly examined, where it may be seen that entangled states encode the angle of magnetic field lines, perceived in animals as differences in reaction rates. Thirdly, it is seen that the superposition of excited states upon light excitation in photosynthesis supports long-lived coherent states, conjectured to explain the efficiency of energy transfer. Secondly, it is conjectured that the signalling in olfaction is also a tunnelling effect, enabled by the presence of an odorant with a signature quantum mechanical vibration. ![]() Firstly, it is shown that the remarkably fast reaction rates of enzymes are accelerated by tunnelling phenomena. ![]() The ways in which the full system is treated involve various degrees of ‘quantumness’ and we shall see briefly how this is done in the four systems that follow. Examining the rate equation, based on Fermi's golden rule, will allow us to consider ‘quantum effects’ and, surprisingly, it will be seen that the protein environment of these systems does not camouflage or collapse any state, but conversely seems not only to enable the said rate but also to further- to enhance- it. Though diverse areas, they have at least two common threads (i) they are biosystems that may be understood in terms of a rate and (ii) they are all biosystems consisting of a pigment (or small, non-protein, molecule such as a ligand/odorant/flavin) in a protein environment. It is shown, beginning with the rate equation, that all these systems may contain some degree of quantumeffect, and where experimental evidence is available, it is explored to determine how the quantum analysis aids in understanding of the process.įour living processes are considered in this review: a reaction mechanism (enzyme catalysis), a sensory signal (olfaction), the transfer of energy (photosynthetic energy capture) and the encoding of information (magnetodetection). They are all (i) effects in biology: rates of a signal (or information) that can be calculated from a form of the ‘golden rule’ and (ii) they are all protein–pigment (or ligand) complex systems. These are biosystems that are very diverse in detail but possess some commonality. But when does the quantum mechanical toolkit become the best tool for the job? This review looks at four areas of ‘quantum effects in biology’. Of course, at the fundamental level all things are quantum, because all things are built from the quantized states and rules that govern atoms. More uncertain, however, is whether or not these concepts are fundamental to biology and living processes. Despite certain quantum concepts, such as superposition states, entanglement, ‘spooky action at a distance’ and tunnelling through insulating walls, being somewhat counterintuitive, they are no doubt extremely useful constructs in theoretical and experimental physics. ![]()
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