BIOENERGETICS

• METABOLISM

  • A highly coordinated cellular activity in which many multi-enzyme systems (metabolic pathways) cooperate.
• Metabolism 


  Obtains chemical energy
• Metabolism

  • Convert nutrient molecules into the cell’s own characteristic molecules
• Metabolism


  A highly coordinated cellular activity in which many multi-enzyme systems (metabolic pathways) cooperate to:

  1. Obtain chemical energy

  2. Convert nutrient molecules into the cell's own characteristic molecules

  3. Polymerize monomeric precursors into biomolecules

  4. Synthesize and degrade biomolecules which may be required for some specialized cellular functions

  
• Types of Metabolism


  • Catabolism
  • Anabolism
• Catabolism


  Breaking down of biochemical fuels to extract energy (energy-yielding processes). Produce energy in the form of ATP and NADPH.
• Anabolism


  Building up of biomolecules necessary to sustain life (energy-requiring)
• Starting materials are broken down into more simpler molecules such as CO2, NH3, and H2O. Then, during catabolic reactions they produce energy in the form of ATP and NADPH. While, in anabolic reactions, they will convert smaller compounds into much bigger compounds, and these anabolic reactions require energy in the form of ATP and NADPH.
• Metabolism entails utilization and production of energy
• Processes involved in metabolism obey the fundamental laws of thermodynamics
• Bioenergetics

  Provide the rules upon which metabolism functions. Field of biochemistry concerned with the transformation and use of energy by living cells, and determines the direction and extent to which biochemical reactions occur.
• Enthalpy (ΔH)


  Measure of the change in heat content of the reactants and products. Governed by the 1st Law of Thermodynamics - "Law of Conservation of Energy" - energy can neither be created nor destroyed, it can only be transformed from one form to another.
• Types of Enthalpy Change

  • Exothermic - heat is released during the course of the reaction; negative (−) ΔH value
  • Endothermic - heat is absorbed during the course of the reaction; positive (+) ΔH value
• Entropy (ΔS)


  A measure of the change in randomness or disorder of reactants and products. Governed by the 2nd Law of Thermodynamics - a process is spontaneous if such process will cause an increase in the entropy of the universe.
• Entropy Change


  • (+) - entropy increases; process is spontaneous
  • (-) - non-spontaneous process
  • 0 - system is at equilibrium
• Gibbs' Free Energy (ΔG)


  Energy available to do work. ΔG = ΔH - TΔS. A variable criterion of the spontaneity of reactions.
• Gibbs' Free Energy Change

  • (-) - Loss of free energy → EXERGONIC; Spontaneous
  • (+) - Gain of free energy → ENDERGONIC; Non-spontaneous
  • 0 - Reaction is in equilibrium
• Rather than burning all of the energy in one reaction, cells release the stored energy in the molecules through a series of oxidation reactions. These oxidation reactions are the pathways involved in cellular respiration. Energy released is converted to ATP, NADH, or FADH2.
• Standard Free Energy Change (ΔG°)

  Obtained experimentally at 25°C and 1 atm. Can be related to the equilibrium constant, Keq, of the reaction.

  ΔG°' if pH = 7.0
• If [reactants] = [products], ΔG = ΔG°'.

  If the reaction is at equilibrium (ΔG = 0), ΔG°'= - RT ln Keq.
• A significant number of metabolic reactions are redox reactions.
• Reducing Agents


  Substances that tend to give up electrons and be oxidized
• Oxidizing Agents

  Substances that tend to accept electrons and be reduced
• LEORA: Loss of Electron, Oxidation, Reducing Agent

  GEROA: Gain of Electron, Reduction, Oxidizing Agent
• Steps in Determining the Overall Net Potential

  Determine the half reactions involved using the standard reduction potential table

  2. Determine the reduction half reaction - Half reaction with a more positive standard reduction potential

  3. Determine the oxidation half reaction - Reverse of the other half reaction, note that the sign becomes positive

  4. Get the sum of the two half reactions to calculate the overall potential - Sum the two half reactions, while for the dissociation equation, the electrons should be first equal before adding them up. Cancel out species present from both sides.

  
• In determining who is the electron acceptor, it is the side where the electrons can be found, the remaining side is the electron donor.
• ∆𝐺°


  Free energy
• E


  Cell potential of the cell at any moment in time
• E°'


  Overall cell potential
• R


  Universal gas constant (8.314 J/mol-K or 1.98 cal/mol-K)
• T


  Temperature in Kelvin
• n


  No. of Electrons Transferred
• F


  Faraday's Constant (96.485 kJ/mol-V or 23.06 kcal/mol-V)
• In determining who is the electron acceptor, it is the side where the electrons can be found, the remaining side is the electron donor
• Co-Enzymes in Biological Oxidation


  Activated Carriers that function to make metabolism more economically manageable and comprehensive
• Roles of Activated Carriers

  • Fuel oxidation (involves NADH and FADH2)
  • Reductive biosynthesis (involves NADPH)
  • Transfer of small fragments (Acetyl CoA and Tetrahydro CoA)
• NAD+/NADH & NADP+/NADPH


  Nicotinamide adenine dinucleotide (phosphate), an active form of niacin (vitamin B3), redox cofactors that can accept a proton and two electrons (equivalent to a hydride ion, :H−) when a substrate molecule is oxidized

  
• NAD+


  Major electron acceptor in oxidation of fuel molecules
• NADPH


  Used almost exclusively in reductive biosynthesis
• FAD/FADH2 & FMN/FMNH2


  Flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), active forms of riboflavin (vitamin B2), redox cofactors that also accept a hydride ion (H+ + 2e−) plus another proton