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Register a new userA new model for magnetoreception
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Certain migratory birds can sense the earths magnetic field. The nature of this process is not yet properly understood. Here we offer a simple explanation according to which birds literally `see the local magnetic field: Our model relates the well-established radical pair hypothesis to the phenomenon of Haidingers brush, a capacity to see the polarisation of light. This new picture explains recent surprising experimental data indicating long lifetimes for the radical pair. Moreover there is a clear evolutionary path toward this field sensing mechanism: it is an enhancement of a weak effect that may be present in many species.
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The mechanism used by migratory birds to orientate themselves using the geomagnetic field is still a mystery in many species. The radical pair mechanism, in which very weak magnetic fields can influence certain types of spin-dependent chemical reactions, leading to biologically observable signals, has recently imposed itself as one of the most promising candidates for certain species. This is thanks both to its extreme sensitivity and its capacity to reproduce results from behavioral studies. Still, in order to gain a directional sensitivity, an anisotropic mechanism is needed. Recent proposals have explored the possibility that such an anisotropy is due to the electron-nucleus hyperfine interaction. In this work we explore a different possibility, in which the anisotropy is due to spin-orbit coupling between the electron spin and its angular momentum. We will show how a spin-orbit-coupling-based magnetic compass can have performances comparable with the usually-studied nuclear-hyperfine based mechanism. Our results could thus help researchers actively looking for candidate biological molecules which may host magnetoreceptive functions, both to describe magnetoreception in birds as well as to develop artificial chemical compass systems.
Is there a functional role for quantum mechanics or coherent quantum effects in biological processes? While this question is as old as quantum theory, only recently have measurements on biological systems on ultra-fast time-scales shed light on a possible answer. In this review we give an overview of the two main candidates for biological systems which may harness such functional quantum effects: photosynthesis and magnetoreception. We discuss some of the latest evidence both for and against room temperature quantum coherence, and consider whether there is truly a functional role for coherence in these biological mechanisms. Finally, we give a brief overview of some more speculative examples of functional quantum biology including the sense of smell, long-range quantum tunneling in proteins, biological photoreceptors, and the flow of ions across a cell membrane.
Chromatin loop extrusion is a popular model for the formation of CTCF loops and topological domains. Recent HiC data have revealed a strong bias in favour of a particular arrangement of the CTCF binding motifs that stabilize loops, and extrusion is the only model to date which can explain this. However, the model requires a motor to generate the loops, and although cohesin is a strong candidate for the extruding factor, a suitable motor protein (or a motor activity in cohesin itself) has yet to be found. Here we explore a new hypothesis: that there is no motor, and thermal motion within the nucleus drives extrusion. Using theoretical modelling and computer simulations we ask whether such diffusive extrusion could feasibly generate loops. Our simulations uncover an interesting ratchet effect (where an osmotic pressure promotes loop growth), and suggest, by comparison to recent in vitro and in vivo measurements, that diffusive extrusion can in principle generate loops of the size observed in the data. Extra View on : C. A. Brackley, J. Johnson, D. Michieletto, A. N. Morozov, M. Nicodemi, P. R. Cook, and D. Marenduzzo Non-equilibrium chromosome looping via molecular slip-links, Physical Review Letters 119, 138101 (2017)
Invited contribution to Quantum Aspects of Life, D. Abbott Ed. (World Scientific, Singapore, 2007).
A model to describe the mechanism of conformational dynamics in protein based on matter interactions using lagrangian approach and imposing certain symmetry breaking is proposed. Both conformation changes of proteins and the injected non-linear sources are represented by the bosonic lagrangian with an additional phi^4 interaction for the sources. In the model the spring tension of protein representing the internal hydrogen bonds is realized as the interactions between individual amino acids and nonlinear sources. The folding pathway is determined by the strength of nonlinear sources that propagate through the protein backbone. It is also shown that the model reproduces the results in some previous works.
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