Hemoglobin Oxygen Binding, Erythrocyte Shape Transformations, and Modeling of Cell Differentiation as Examples of Theoretical Approaches in Studying the Structure-Function Relationship in Biological Systems
Any attempt to express functional behavior of a biological system in terms of the physical and chemical properties of its constituents must involve relating together different levels of complexity of a system’s structure. At different levels of the system, the structures are described by different observable quantities determinable by different experimental approaches. The understanding of the macroscopic behavior of a certain structure, including its function, on the basis of its microscopic properties can be in many instances achieved simply by correlating the observations obtained at different levels of study. However, in many other instances such an understanding is possible only on the basis of quantitative relationships which are the result of an appropriate theory. Theoretical approaches in biology play the same role as theoretical approaches in physics and chemistry, such as statistical mechanics where the thermodynamic properties of the system are determined on the basis of properties of atoms and molecules and their interactions, or quantum chemistry where properties of atoms and molecules are determined from interactions between the constituents of the atom. Biological systems comprise a large number of different levels of organization, from atoms and molecules to macromolecules, solutions, supramolecular structures, cells, cell populations, tissues, organs, organisms, etc. Relating system properties at two such levels must take into consideration specific features in the description of a system at a given level and it is expected that the corresponding theory reflects these features. Therefore many different theoretical approaches need to be developed in order to cover all possible relationships. These lectures are aimed at giving an example of three different theoretical approaches, each relating a different pair of levels of structural complexity in biological system. The relations between the macrómolecular structure and the thermodynamic behavior of the system of a macromolecule and its ligands will be dealt with in the lecture on the relationship between hemoglobin structure and its ligand binding behavior. Relationship between the cell shape and the properties of the cell membrane will be discussed in the lecture on interaction of charged membranes with surrounding ions and ion induced shape and volume changes of red blood cell ghosts. The properties of the cell population will be related to the properties of a chemical system at the level of a single cell in the lecture on modeling the molecular basis of cell differentiation. Although the topics discussed in these lectures are all connected with the system of oxygen delivery in vertebrate organisms, they represent rather different aspects of this system and therefore the material is organized in such a way that each lecture is contained in a separate chapter. Chapters are independent and selfsufficient as regards the nomenclature. References are also listed separately for each chapter.
KeywordsStable Steady State Oxygen Binding Hemoglobin Molecule Electrostatic Free Energy Murine Erythroleukemia Cell
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