Bio-chemical Energetics

Bio-chemical Energetics

Definition of Bio-chemical Energetics or Bioenergetics:
Study of the inter conversion of forms of energy in biological system.

The Concept of Free Energy:

Free Energy (G): The component of the total energy of a system that can do work at constant temperature and pressure.

Free energy change (∆G): The amount of free energy released (negative ∆G) or absorbed (positive ∆G) in a reaction at constant temperature and pressure.

The first law of thermo dynamics states that energy cannot be created or destroyed but this law cannot be used to predict whether a reaction can occur spontaneously.
The second law of thermo dynamics states that a process can occur spontaneously, only if the sum of the entropies of the system and its surroundings increases.
Since the entropy changes of chemical reactions are not readily measurable, the entropy is not used as a criterion whether a biochemical process can occur spontaneously or not.

In 1878, Gibbs created the free energy function by combining the first and second laws of thermodynamics in the form of following equation.


Exergonic Reaction: Spontaneous reaction, ∆G value is negative. Do not need energy supply from outside. (Breakdown Reaction)
Endergonic Reaction:
Non spontaneous, thermo dynamically unfavorable reaction. ∆G is positive or more than zero. Reaction will occur only when energy supplied to the system. (Synthetic Reaction)

Energy Rich Compounds:

Developed by Fritz Lipman, characterized by high energy bonds which have large free energy of hydrolysis. Energy rich compounds are symbolized by wriggle bonds.
1) Low energy bonds ∆ G value is- 1 to 5 Kcal/mole
2) High energy bonds ∆ G value is – 7 to 15 Kcal/mole

Exhibit a large decrease free energy (A G) on hydrolysis e.g. creative phosphate, arginine phosphate, phosphoenol pyruvate, Acetyl phosphate, ADP, ATP, Acyl, CoA. (With energy value)

Coupling of Reactions: In the cell, the energy released or made available in an exergonic reaction is utilized to drive other endergonic reactions and thereby made to do works. The only way this can occur is by common reactants in a process known as the coupling of reactions.

Components of Electron Transport Chain:
1) Nicotinamide nucleotides
2) Flavoproteins
3) Nonheme Iron Proteins
4) Quinones
5) The Cytochromes

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