Oxidation-Reduction
important reaction type in
biochemistry
Electron transfer reaction
many different types of reactions
Oxidation and reduction have to
occur simultaneously
Definitions
Oxidation
Reduction
Loss of electrons
Gaining of electrons
Gaining of oxygen
Loss of oxygen
Loss of Hydrogen
Gaining of Hydrogen
Loss of electrons/Gaining of electrons
Loss of electrons/Gaining of electrons
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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