Basic Concepts in Bioenergetics

Abstract

A living cell is an open thermodynamic system which can exchange heat and matter with the surrounding world; the surrounding for a unicellular organism is represented by the environment in which it lives and for a multicellular organism by the adjacent cells with which a functional interrelation can exist. Cells are however also multicomponent systems, often subdivided into separate compartments, the intracellular organelles; this situation can be thermodynamically described as a multiphase system, in which the water phase, the predominant phase in a cell, is divided into multiple compartments by a different phase, the biological membranes. The thermodynamic equilibration within a phase implies that all intensive properties are constant throughout the volume of the phase itself (temperature, pressure, electric potential and chemical potentials). This constancy of the thermodynamic parameters does not apply, strictly speaking, to a narrow region adjacent to the boundary between phases; this interphase region is an independent part of the system, characterized by its own properties, different from those of the bulk phase.