Thermodynamics and life Lecture outline • Basic concepts of non-equilibrium thermodynamics of living systems • Diffusion • Osmosis and osmotic pressure Basic concepts of non-equilibrium thermodynamics of living systems • There is an internal „source“ of entropy in non-equilibrium systems. • The amount of entropy produced per unit volume in unit time is called the entropy production rate s. Prigogine principle • For states not too far from tmd. equilibrium, the Prigogine principle applies: At constant external conditions, an open system spontaneously proceeds towards a state with a minimum entropy production rate. • This state is called a stationary state (in biology: state of dynamic equilibrium, homeostasis respectively). Difference between an equilibrium and stationary state Difference between an equilibrium and stationary state Difference between an equilibrium and stationary state Fluctuations and generalised le Chatelier principle • Fluctuations are small deviations from the equilibrium or stationary state arising from internal stochastic (random) processes. Small disturbances are small deviations from the equilibrium or stationary state arising from external processes. Dissipative structures • Ordered non-equilibrium time-space structures are called dissipative structures. We cannot apply Boltzmann formula on them. According to Prigogine, they originate as a consequence of a fluctuation. They are stabilised by energy exchange with environment. The dissipative structures belong among problems solved by non-linear non-equilibrium thermodynamics. They can appear only in conditions far enough from equilibrium and a sufficient energy and substance flow is necessary. (Example: „Bénard instability“) Autocatalytic reactions • A general equation of the autocatalytic reaction: nA + X ¬ݯ 2X + (n - 1)A, It can be followed by: X ¬ݯ F • In the autocatalytic reaction, a compound X is formed from compound A under in presence of the substance X. It means that the substance X acts as a catalyst in its formation. When the substance A is available in sufficient amount, the amount of X grows exponentially. F can be a product formed from compound X. • Autocatalytic reaction of it's kind is also the replication of DNA. It should be admitted that a complex of „common“ chemical reactions can demonstrate itself as an autocatalytic reaction. • The replication of DNA is a complex of metabolic processes which results in formation of a copy carrying the same genetic information. Belousov-Zhabotinsky reaction Examples of thermodynamic approach to problem solution: Non-equilibrium thermodynamics: Diffusion Equilibrium thermodynamics: Osmosis Diffusion as an irreversible process • Transport process - tmd. system proceeds towards equilibrium state, in which concentrations of all present substances are equalised in whole volume. • The flow of diffusing substance is constant when there is no significant change of its concentration on both sides of the (permeable) membrane (e.g., when the process is slow, volumes are large or active transport is present). • Density of diffusion flow J – amount of substance passing through unit area of a boundary in unit time: 1st Fick law Diffusion coefficient • Approximate formula for the diffusion coefficient was derived by A. Einstein: 2^nd Fick law Osmosis and osmotic pressure Solvent can pass through the membrane but not the solute. System proceeds to tmd. equilibrium by equalisation of concentrations of substances in the whole system by solvent diffusion from space I into the space II. Result: pressure increase in space II. Pfeffer experiment van't Hoff formula P = c.R.T P is osmotic pressure [Pa] c concentration of dissolved compound (n/V) R universal gas constant T thermodynamic temperature • Better fitting (approaching) formula: P = m'.R.T m' is molality (substance amount in 1 litre of solvent). van't Hoff formula For electrolytes: P = i.c.R.T i is dimensionless van't Hoff correction factor, which says how many times more particles are present in solution than the original number of dissolved non-dissociated particles (molecules). The product i.c is sometimes called osmolar concentration or osmolarity with unit osmol.l^-1. A strong electrolyte with concentration of 1 mol.l^-1, dissociating into two ions, has the osmolar concentration 2 osmol.l^-1 and double the osmotic pressure of a non-dissociating compound of the same concentration. The osmotic pressure of blood plasma or interstitial fluid is about 770 kPa. (1 M solution of a non-dissociating compound has osmotic pressure 2,58 MPa at the same temperature). Oncotic pressure (3,3 kPa) Tonicity of solutions • solutions having osmotic pressure lower than blood plasma has are hypotonic, with the same pressure are isotonic, and with higher pressure than blood plasma are hypertonic. • endoosmosis: haemolysis • The range of concentrations of hypotonic solutions in which partial or full haemolysis does not occur = osmotic resistance of erythrocytes. • exoosmosis: plasmorrhysis (in plants - plasmolysis) • receptors (volumoreceptors in kidneys and osmoreceptors in hypothalamus) How does it look? Author: Vojtěch Mornstein Language revision: Carmel J. Caruana Presentation design: - - - Last revision: June 2009