Oxidation-Reduction important reaction type in biochemistry Electron transfer reaction many different types of reactions Oxidation and reduction have to occur simultaneously

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

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  S surroundings 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 (CO 2 for example) increase the randomness of the surroundings Heat is given off increasing the randomness of the surroundings Overall,  S univ >0