Nyi Mekar Saptarini

The ability to harness energy & change it into biological work is a fundamental property of organism.

Organisms carry out variety of energy transductions, conversions of one form of energy to another.

They use the chemical energy in fuels to synthesis of complex, highly ordered macromolecules from simple precursors.

They convert the chemical energy of fuels into concentration gradients & electrical gradients, into motion, heat, and light (few organisms).

Bioenergetics and Thermodynamic

Bioenergetics and Thermodynamics Bioenergetics is the quantitative study of the

energy transductions in cells and of the nature and function of the chemical processes underlying these transductions.

Bioenergetics obey the Laws of Thermodynamics

Thermodynamics 1st law : the principle of the conservation of energy : for any

physical or chemical change, the total amount of energy in

the universe remains constant; energy may change form or it

may be transported from one region to another, but it

cannot be created or destroyed.

2nd law : the universe always tends toward increasing

disorder: in all natural processes, the entropy of the universe

increases.

3 thermodynamic quantities

1. Gibbs free energy, G energy capable of doing work during a

reaction at constant T & P. Reaction proceeds with the release of free

energy G is negative value (exergonic). Reaction make the system gains free energy

G is positive value (endergonic). Unit : joules/mole or calories/mole.

2. Enthalpy, H Heat content of the reacting system. It reflects the number and kinds of chemical

bonds in the reactants and products. Reaction releases heat H is negative value

(exothermic). Systems take up heat from surroundings H is

positive values (endothermic). Unit : joules/mole or calories/mole. 1 cal = 4.184 J

G = H - TS

3. Entropy, S expression for the randomness or disorder in a

system. Products of a reaction are less complex & more

disordered than the reactants gain in entropy S is positive value.

Unit : joules/mole.Kelvin (J/mol.K)

Perubahan energi bebas

G = H - TS

G: Perubahan energi bebas Energi yang digunakan untuk

melakukan kerja.

Mendekati nilai nol bila reaksi

mendekati kesetimbangan.

Meramalkan apakah reaksi

favorable.

H: Perubahan entalpi Kalor yang dilepaskan atau diserap

selama reaksi berlangsung.

Tidak dapat meramalkan apakah

reaksi favorable

S: Perubahan entropi Ukuran ketidak teraturan

Tidak dapat meramalkan apakah

reaksi favorable.

Perubahan energi bebas

Awal Awal

AwalAkhir

AkhirAkhir

G < 0 G > 0

G = 0

Koordinat reaksi

E

n

e

r

g

i

b

e

b

a

s

(

G

)

A B A B B A

Exergonic Endergonic

Equilibrium

Cells Require Sources of Free Energy Cells are isothermal systems. Heat flow is not a source of energy for cells. Cells can and must use is free energy. Cells acquire free energy from nutrient

molecules. Photosynthetic cells acquire it from solar

radiation. Cells transform free energy into ATP and

other energy-rich compounds.

Standard Free-Energy Change The composition of a reacting system (reactants

& products) tends to continue changing until equilibrium is reached.

The concentrations of reactants and products at equilibrium define the equilibrium constant, Keq.

Standard conditions (298 K) : reactants & products are 1 M or for gases are 101.3 kPa or 1 atm, the force driving the system toward equilibrium is defined as the standard free-energy change, G.

Cells : H+ is 107 M (pH 7) & water is 55.5 M; for reactions that involve Mg 2+, concentration is 1 mM standard transformed constants (G& Keq)