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

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Loss of electrons/Gaining of electrons

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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

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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

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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?

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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

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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:

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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

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•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

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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

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Exergonic vs. Endergonic Reactions

• Products have more energy than reactants

• Energy gained by system

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Exergonic v. endergonic reactions

• Products have less energy than reactants

• Energy released• Available to do work• spontaneous

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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

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The Big Picture Energy Interconversion in Living Organisms

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

entropy?

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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

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