Biophysics: An Introduction
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Biophysics is the science of physical principles underlying all processes of life, including the dynamics and kinetics of biological systems.
This fully revised 2nd English edition is an introductory text that spans all steps of biological organization, from the molecular, to the organism level, as well as influences of environmental factors. In response to the enormous progress recently made, especially in theoretical and molecular biophysics, the author has updated the text, integrating new results and developments concerning protein folding and dynamics, molecular aspects of membrane assembly and transport, noise-enhanced processes, and photo-biophysics. The advances made in theoretical biology in the last decade call for a fully new conception of the corresponding sections. Thus, the book provides the background needed for fundamental training in biophysics and, in addition, offers a great deal of advanced biophysical knowledge.
the amino acids. The buffer capacity, as well as the dissociation property of these substances can be investigated by titration experiments. This furthermore allows us to calculate the dynamics of molecular charges of these molecules. In Fig. 2.30 the charge of glycine is demonstrated as a function of the pH 2.2 Molecular and Ionic Interactions as the Basis for the Formation 65 Fig. 2.30 The average number of charges (z) of glycine plotted against pH in the solution (pK1 ¼ 2.35, pK2 ¼ 9.78)
not need the RT-term. It becomes: p ¼ g0 c0s (3.106) Introducing this into Eq. 3.105 and rearranging, results in: 1 g0 ¼Wþ p cs (3.107) If now the value 1/cs is plotted against 1/p, a linear function appears, indicating W as the point at which the ordinate is crossed at 1/p ! 0, and g0 as the slope. This is done in Fig. 3.13 for sucrose, polyethylene glycole (M ¼ 400), and bovine serum albumin (BSA) (to fit in the same figure, the molal and osmolal values for BSA were multiplied by 100!). The
permselective. This means that all components of the solution can more or less penetrate the membrane. We will analyze this situation in detail later using the approaches of nonequilibrium thermodynamics (Sect. 3.3.1). Upon consideration of the corresponding flux matrix (Eq. 3.147) the following relation is derived: ss ¼ nw À ns nw (3.109) Using the indices of the Van’t Hoff’s equation, vw and vs represent the rate of movement of the solvent (water) and the solute in the membrane. In the case
transmembrane potential of cells without microelectrodes. The chloride distribution can be easily determined using the radioisotope 36Cl. Sometimes one can use other small charged organic molecules, which penetrate the membrane quickly, and are labeled by 3H or 14C. Knowing the distribution of these ions, the membrane potential (Dc) can be calculated according to Eq. 3.112. Furthermore, the Nernst equation allows the calculation of electrode potentials. If a metal is dipped into an electrolyte
profile results from the bulk concentrations in both phases, and from its passive distribution in the electric field. Integrating the Nernst–Planck equation (3.157) with these conditions, one gets the following expression: Ji ¼ ÀPi b cIi À cIIi eb 1 À eb with : b¼ zi F Dc RT (3.160) The function J ¼ f(Dc) is illustrated in Fig. 3.23. It considers the flux of a monovalent cation (zi ¼ +1) penetrating the membrane with a permeability Pi ¼ 10À7 msÀ1. Let the flux (Ji) be positive if it is