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10 - A chemical compass for bird navigation
- from Part III - Quantum effects in higher organisms and applications
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- By Ilia A. Solov'yov, University of Southern Denmark (SDU), Thorsten Ritz, Department of Physics and Astronomy, Irvine, CA, Klaus Schulten, University of Illinois, Peter J. Hore, University of Oxford
- Edited by Masoud Mohseni, Yasser Omar, Gregory S. Engel, University of Chicago, Martin B. Plenio, Universität Ulm, Germany
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- Book:
- Quantum Effects in Biology
- Published online:
- 05 August 2014
- Print publication:
- 07 August 2014, pp 218-236
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Summary
Introduction
Migratory birds travel spectacular distances each year, navigating and orienting by a variety of means, most of which are poorly understood. Among these is a remarkable ability to perceive the intensity and direction of the Earth's magnetic field (Mouritsen and Ritz, 2005; Wiltschko and Wiltschko, 2006; Johnsen and Lohmann, 2008). Biologically credible mechanisms for the detection of such a weak field (25–65 μT) are scarce, and in recent years just two proposals have emerged as front-runners. One, essentially classical, centers on clusters of magnetic iron-containing particles in the upper beak, which appear to act as a magnetometer for determining geographical position (Kirschvink and Gould, 1981; Kirschvink et al., 2001; Fleissner et al., 2007; Solov'yov and Greiner, 2007; Walker, 2008; Solov'yov and Greiner, 2009a, b; Falkenberg et al., 2010). The other relies on the quantum spin dynamics of transient photoinduced radical pairs (Schulten et al., 1978; Schulten, 1982; Schulten and Windemuth, 1986; Ritz et al., 2000b; Cintolesi et al., 2003; Möller et al., 2004; Mouritsen et al., 2004; Heyers et al., 2007; Liedvogel et al., 2007b, a; Solov'yov et al., 2007; Feenders et al., 2008; Maeda et al., 2008; Solov'yov and Schulten, 2009; Ritz et al., 2009; Rodgers and Hore, 2009; Zapka et al., 2009). Originally suggested by Schulten in 1978 (Schulten et al., 1978) as the basis of the avian magnetic compass sensor, this mechanism gained support from the subsequent observation that the compass is light dependent (Wiltschko et al., 1993) (for a review see e.g. (Wiltschko et al., 2010)).
Photosynthetic apparatus of purple bacteria
- Xiche Hu, Thorsten Ritz, Ana Damjanović, Felix Autenrieth, Klaus Schulten
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- Journal:
- Quarterly Reviews of Biophysics / Volume 35 / Issue 1 / February 2002
- Published online by Cambridge University Press:
- 09 May 2002, pp. 1-62
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1. Introduction 2
2. Structure of the bacterial PSU 5
2.1 Organization of the bacterial PSU 5
2.2 The crystal structure of the RC 9
2.3 The crystal structures of LH-II 11
2.4 Bacteriochlorophyll pairs in LH-II and the RC 13
2.5 Models of LH-I and the LH-I-RC complex 15
2.6 Model for the PSU 17
3. Excitation transfer in the PSU 18
3.1 Electronic excitations of BChls 22
3.1.1 Individual BChls 22
3.1.2 Rings of BChls 22
3.1.2.1 Exciton states 22
3.1.3 Effective Hamiltonian 24
3.1.4 Optical properties 25
3.1.5 The effect of disorder 26
3.2 Theory of excitation transfer 29
3.2.1 General theory 29
3.2.2 Mechanisms of excitation transfer 32
3.2.3 Approximation for long-range transfer 34
3.2.4 Transfer to exciton states 35
3.3 Rates for transfer processes in the PSU 37
3.3.1 Car→BChl transfer 37
3.3.1.1 Mechanism of Car→BChl transfer 39
3.3.1.2 Pathways of Car→BChl transfer 40
3.3.2 Efficiency of Car→BChl transfer 40
3.3.3 B800-B850 transfer 44
3.3.4 LH-II→LH-II transfer 44
3.3.5 LH-II→LH-I transfer 45
3.3.6 LH-I→RC transfer 45
3.3.7 Excitation migration in the PSU 46
3.3.8 Genetic basis of PSU assembly 49
4. Concluding remarks 53
5. Acknowledgments 55
6. References 55
Life as we know it today exists largely because of photosynthesis, the process through which light energy is converted into chemical energy by plants, algae, and photosynthetic bacteria (Priestley, 1772; Barnes, 1893; Wurmser, 1925; Van Niel, 1941; Clayton & Sistrom, 1978; Blankenship et al. 1995; Ort & Yocum, 1996). Historically, photosynthetic organisms are grouped into two classes. When photosynthesis is carried out in the presence of air it is called oxygenic photosynthesis (Ort & Yocum, 1996). Otherwise, it is anoxygenic (Blankenship et al. 1995). Higher plants, algae and cyanobacteria perform oxygenic photosynthesis, which involves reduction of carbon dioxide to carbohydrate and oxidation of water to produce molecular oxygen. Some photosynthetic bacteria, such as purple bacteria, carry out anoxygenic photosynthesis that involves oxidation of molecules other than water. In spite of these differences, the general principles of energy transduction are the same in anoxygenic and oxygenic photosynthesis (Van Niel, 1931, 1941; Stanier, 1961; Wraight, 1982; Gest, 1993). The primary processes of photosynthesis involve absorption of photons by light-harvesting complexes (LHs), transfer of excitation energy from LHs to the photosynthetic reaction centers (RCs), and the primary charge separation across the photosynthetic membrane (Sauer, 1975; Knox, 1977; Fleming & van Grondelle, 1994; van Grondelle et al. 1994). In this article, we will focus on the anoxygenic photosynthetic process in purple bacteria, since its photosynthetic system is the most studied and best characterized during the past 50 years.