Molecular thermodynamics for cell biology as taught with boxes.

MAYORGA, LS; LÓPEZ, MJ; BECKER, WM

Mendoza

Congreso; 48º SAIB; 2012

SAIB

Thermodynamic principles are basic to an understanding of the complex fluxes of energy and information that are required to keep cells alive. These microscopic machines are non-equilibrium systems at the micron scale that are maintained in pseudo-steadystate conditions by very sophisticated processes. Therefore, several non-standard concepts need to be taught to rationalize why these very ordered systems proliferate actively all over our planet despite the second law of the thermodynamics. We propose a model consisting of boxes with different shapes containing small balls that are in constant movement because a stream of air is blowing from below. This is a simple macroscopic system that can be easily visualized by students and that can be understood as mimicking the behavior of a set of molecules exchanging energy. With such boxes, the basic concepts of entropy, enthalpy, and free energy can be taught while maintaining a molecular understanding of the concepts and stressing the stochastic nature of the thermodynamic laws. In addition, time-related concepts such as reaction rates and activation energy can be readily visualized. Moreover, the boxes provide an intuitive way to introduce the role of information and Maxwell's demons operating under non-equilibrium conditions on the cellular organization.