Thermodynamic Concepts biophisics

THERMODYNAMIC CONCEPTS

• 1st thermodynamic principle: HEAT: ENTHALPY concept • 2nd thermodynamic principle: ENTROPY • GIBBS FREE ENERGY

• BIOCHEMICAL EXEMPLES

Master en Nanscience and Nanotechnology 2008-09 Dr. TERESA MAIRAL

THERMODYNAMIC CONCEPTS

In thermodynamics three types of systems are studied: ISOLATED (or adiabatic) : systems completely autonomous, exchanging neither material nor energy with their surroundings. CLOSED: CLOSED materially self-contained, but exchange energy across their boundaries. OPEN: OPEN exchange both energy and material with the environment

THERMODYNAMIC CONCEPTS

1st thermodynamic principle: HEAT: ENTHALPY concept It is the manifestation of the internal energy of a system. In 1842 Julius Meyer established the equivalence between heat and energy: 1st principle of thermodynamic: principle of conservation of energy SETTING UP THE ENERGY IS NEITHER CREATED NOR DESTROYED, JUST CHANGING. The heat spreads through 3 mechanisms: conduction, convection and radiation Conduction: Conduction direct contact between the heat source and the body: FOURIER LAW Convection: Convection when there is a translation of particles presents in a fluid moving from cold to hot spots and vice. Radiation: Radiation It is the process by which the heat in the form of radiant energy is transmitted into the vacuum, using electromagnetic waves.

THERMODYNAMIC CONCEPTS E is an extensive property, whose units in thermodynamic problems are calories or joules (1 cal = 4.184 J or electron-volts (1 eV = 1.6 x 10-19 J).

The internal energy E of a system is altered by exchange of work, W and heat Q with the surroundings. ∆E or ∆U = Q+W

dE = δQ+δW

(1)

The pressure-volume work (pV) done on the surroundings by a systems changing its volume against an external pressure p is: δW= -pdV ENTHALPY concept

H=E + pV

(2)

dH = δE+pdV (1) and (2) ∆H=Q

.H < 0--> the reaction is exothermic and heat is given off. H > 0--> the reaction is endothermic and heat is absorbed

THERMODYNAMIC CONCEPTS

2nd thermodynamic principle: ENTROPY For any spontaneous process, the Entropy(disorder) of the universe, .Suniverse, must increase. "The amount of entropy of any isolated system thermodynamically tends to increase with time“ ENTROPY: it is the disorder DEGREE OF A SYSTEM: BOLZMAN law S=klnW where k = Boltzmann’s constant, which equals R, the gas constant (8.31 J °K-1mol-1) divided by Avogadro’s number, = 1.38 X 10-23 J/°K. ∆S = S(2)- S(1)= kln W2/W1

THERMODYNAMIC CONCEPTS

Relation between Heat and Entropy Change: The 19th century physicist, Clausius, proposed that the differential entropy change, dS, is proportional to the heat absorbed,dQrev, for a reversible process, with 1/T : dS= dQrev/T MORE ENTROPY-----MORE DISORDER----LOW INFORMATION In a CLOSED systems a process will occur SPONTANEOUSLY if the entropy of the system + its surroundings increases. In an open system (alive systems), the disorder is the return results of two processes: the exchange-system environment and changes that occur in the interior. Non-Isolated System (dS ≥ dQ/T) In an isolated system, the art on the inside moves to a state of equilibrium where the disorder is maximum (dS ≥ 0)

THERMODYNAMIC CONCEPTS

???????? HOW WE ARE GOING TO MEASURE THE ENTROPY CHANGES IN THE REST OF THE UNIVERSE CAUSED BY THE ENERGY FLOW ACROSS THE BOUNDARY OF THE SYSTEM??????-------- NOT POSSIBLE !!! however ===> we need a criterion of spontaneity which applies to our system (organism). At constant Temperature and Pressure (conditions under which we exist, more or less): it is possible to calculate the entropy from the flow of ENTHALPY (heat) across the boundaries of the system. The thermodynamic function that links ENTHALPY—ENTROPY: GIIBBS ENERGY: information about if a process is or not favourable, and is a quentitative measure of the net driving force flow at constant temperature and pressure conditions.

Gibbs Free Energy = . ∆ G

∆ G =∆ H-T∆ S

THERMODYNAMIC CONCEPTS

Gibbs Free Energy = . ∆ G

∆ G =∆ H-T∆ S

G 0 -- The net reaction will be in the reverse direction G = 0 -- The reaction is at equilibrium, Γ and no net change in either direction occurs aA + bB === cC + dD

Γ= observed mass action ratio not equilibrium

Keq= equilibrium R = Ideal Gas Const. (1.99 cal mole-1 deg-1); T = is the Absolute Temperature (°Kelvin)

THERMODYNAMIC CONCEPTS

Gibbs energy content of a reaction Vs displacement from equilibrium

A

B

(a) Any change in Γ away from the equilibrium requires an increase in the Gibbs energy : not spontaneous (b) Slope=0 : Equilibrium ∆ G° = - R T ln [B]b / [A]a= - R T ln Keq (c) When the reaction has not yet proceeded as far as equilibrium, a conversion of A to B results is a decrease in G : the mechanism exist (d) The slope of the curve decreases as equilibium is approached. (e) The reaction requiere an input of Gibbs energy: not spontaneaus

THERMODYNAMIC CONCEPTS

BIOCHEMICAL EXEMPLES CATABOLIC REACTIONS OF METABOLISM

ATP + H2O

ADP + Pi

ATP has more free energy than ADP and Pi ��The free energy change for this reaction, ∆G, is less than 0 and the reaction is favorable, i.e. it is Exergonic.

THERMODYNAMIC CONCEPTS

BIOCHEMICAL EXEMPLES CATABOLIC REACTIONS OF METABOLISM

ATP Provides Energy for: •Mechanical Work: Muscle contraction, flagella and cilia movement etc. •Transport Work: Pumping ions and molecules across membranes against a concentration gradient •Chemical Work: Coupling energy from ATP to Endergonic reactions to make them go

THERMODYNAMIC CONCEPTS

THERMODYNAMIC CONCEPTS

BIOCHEMICAL EXEMPLES Energy coupling by phosphate transfer Glutamate + Ammonia

Glutamine ∆Go = +3.4 kcal/mole

This reaction is catalyzed by an enzyme in two steps Energetically, this can be described as the sum of the following two reactions : Glu + NH3 ----> Glu-NH2 + H2O ∆ Go = +3.4 kcal/mole ATP + H2O ----> ADP + Pi ∆ Go = -7.3 kcal/mole

Glu + NH3 + ATP ----> Glu-NH2 + ADP + Pi ∆ Go = - 3.9 kcal/mole

THERMODYNAMIC CONCEPTS

BIOCHEMICAL EXEMPLES PROTEIN DENATURATION

Protein denaturation. (A) Schematic diagram of the initial and final final states of a native → denatured transition

Tm is defined by the temperature of the equilibrium, ∆G=0 between the native and denatured states

Tm= ∆H/ ∆S

BIBLIOGRAPHY Molecular biophysics part: Biophysics, W. Hoppe, W. Lohmann, H. Markl, H. Ziegler (eds). Springer-Verlag, Berlin, 1983. Chapter 3. (Chapters 1 and 2 are recommended for students with no previous exposure to biology/biochemistry although in this case a better introduction would be a general Biochemistry book such as Lehninger’s “Biochemistry”). Bioenergetics part: Bioenergetics3, D.G. Nicholls, S.J. Ferguson, Academic Press, Amstedam, 3rd ed, 2002. Chapters 3 and 4. Bioelectrochemistry: Electrode Dynamics, A.C. Fisher, Oxford University Press, Oxford, 1996.