Redoxtherm

Oxidation-Reduction

important reaction type in biochemistry

Electron transfer reaction

many different types of reactions

Oxidation and reduction have to occur simultaneously

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Definitions

Reduction

Gaining of electrons

Loss of oxygen

Gaining of Hydrogen

Oxidation

Loss of electrons

Gaining of oxygen

Loss of Hydrogen


Loss of electrons/Gaining of electrons


Loss of electrons/Gaining of electrons

• Which species is being oxidized?• Which species is being reduced?• Importance of this reaction? • One step in gluconeogenesis (formation of

glucose)• The reverse reaction occurs when vigorously

contracting muscles function under low oxygen conditions


Thermodynamics

• Study of energy• Important to understanding biochemistry• Two key terms:

• Enthalpy H : Heat of reaction at constant pressure

• Endothermic: Require heat +H

• Exothermic: Releases heat -H

• Change in Entropy S : Change in Randomness


First Law of Thermodynamics

• Energy is conserved during the course of a chemical change

• Energy can be transformed into one form from another

• Energies: Potential, Kinetic, Light, Heat• Example: What happens when you dive off a

diving board into a pool?


Second Law of Thermodynamics

S univ> 0 for a Spontaneous Reaction

• What does this mean?

• Reactions happen without outside intervention when the entropy (randomness) of the universe increases. S univ is the change in entropy


Spontaneous Reactions

• Spontaneous Reactions are Thermodynamically Favored Reactions

• Entropy of the universe (S univ)=entropy of the system + entropy of surroundings

• The change in entropy of univ has to be positive S univ> 0 for a spontaneous reaction. • Note that S system can be negative if Ssurroundings is

sufficiently positive to overcome it • Examples:


Spontaneous Reactions

• Gibbs-Helmhotz equation describes the second law in terms of Free energy (G)

• Free energy is derived from the Second Law. It is the same thing using different terms.

• It is the amount of work that the system can do or the amount of work needed for the system


•Spontaneous Reactions

• Free energy has to be released from the system if the process is spontaneous

• For a spontaneous process: Gsys is negative or Gsys < 0• These reactions are thermodynamically favored• These reactions are said to be exergonic• Amount of energy available to do work


Non-Spontaneous Process

• For a non-spontaneous process: S univ < 0

Gsys is positive or Gsys > 0• These reactions are not thermodynamically

favored• These reactions are said to be endergonic


Exergonic vs. Endergonic Reactions

• Products have more energy than reactants

• Energy gained by system


Exergonic v. endergonic reactions

• Products have less energy than reactants

• Energy released• Available to do work• spontaneous


Linking of exergonic to endergonic reactions (reaction coupling)

• In biochemical systems, an exergonic reaction is used to drive an endergonic one

• In other words, the free energy released in one reaction is used as the free energy needed in another reaction

• Example: cooking food• Example: Hydrolysis of ATP is used in many

reactions to drive another reaction such as formation of macromolecules


The Big Picture Energy Interconversion in Living Organisms

What is the relationship between energy, metabolism, heat, and

entropy?


The Big Picture Energy Interconversion in Living Organisms

• There is Potential Energy Stored in Nutrients (animal cell) or Sunlight (plant cell)

• Convert some of this potential energy through chemical transformations in the cell to do work

• Macromolecules within the cell are formed: Entropy is decreased in the system

• However, products of metabolism (CO2 for example) increase the randomness of the surroundings

• Heat is given off increasing the randomness of the surroundings

• Overall, S univ >0


Redoxtherm

Documents

endergonic reactions

heat of reaction

reactants energy

energy available

favored reactions entropy

exergonic reaction

reaction example

chemical change energy