Bioenergetics

• Bioenergetics

  The field of biochemistry concerned with the energy transformation and use of energy by living cells
• Bioenergetics

  The part of biochemistry concerned with the energy involved in making and breaking of chemical bonds in the molecules found in biological organisms
• Bioenergetics


  The study of energy relationships and energy transformations and transductions in living organisms
• Bioenergetics

  • Focuses on how cells transform energy, often by producing, storing or consuming adenosine triphosphate (ATP)
  • Bioenergetic processes, such as cellular respiration or photosynthesis, are essential to most aspects of cellular metabolism, therefore to life itself
  • An active area of biological research that includes the study of the transformation of energy in living organisms and the study of thousands of different cellular processes such as cellular respiration and the many other metabolic and enzymatic processes that lead to production and utilization of energy in forms such as ATP molecules
• Exergonic reaction

  Reaction that releases energy from a spontaneous chemical reaction without any concomitant utilization of energy
• Exergonic reactions

  • Significant in terms of biology as these reactions have an ability to perform work and include most of the catabolic reactions in cellular respiration
  • Most of these reactions involve the breaking of bonds during the formation of reaction intermediates as is evidently observed during respiratory pathways
  • The bonds that are created during the formation of metabolites are stronger than the cleaved bonds of the substrate
  • The release of free energy, G, in an exergonic reaction (at constant pressure and temperature) is denoted as ΔG = Gproducts - Greactants < 0
• Endergonic reactions

  Reactions that are non-spontaneous and require an input of free energy
• Endergonic reactions

  • Most of the anabolic reactions like photosynthesis and DNA and protein synthesis are endergonic in nature
  • Reactions with a positive ΔG (ΔG > 0), on the other hand, require an input of energy and are called endergonic reactions
  • In this case, the products, or final state, have more free energy than the reactants, or initial state
• Spontaneous

  A reaction will take place without added energy, but it doesn't say anything about how quickly the reaction will happen
• Activation energy

  The initial energy input, which is later paid back as the reaction proceeds, that is required for even energy-releasing (exergonic) reactions to get going
• To get the bonds into a state that allows them to break, the molecule must be contorted (deformed, or bent) into an unstable state called the transition state
• Coupled reaction

  The class of organic reactions that involve the joining of two chemical species
• Organisms often couple the hydrolysis of ATP (adenosine triphosphate) to generate ADP (adenosine diphosphate) as the spontaneous coupling reaction
• Laws of thermodynamics

  Define a group of physical quantities, such as temperature, energy and entropy, that characterize thermodynamic systems in thermodynamic equilibrium, and establish relationships between them
• First law of thermodynamics

  Energy can neither be created nor destroyed; energy can only be transferred or changed from one form to another
• The equation for the first law of thermodynamics is given as ΔU = q + W, where ΔU is the change in internal energy of the system, q is the sum of heat transfer between system and surroundings, and W is the work interaction of the system with its surroundings
• Second law of thermodynamics

  The entropy of any isolated system always increases, and the entropy of the universe (the ultimate isolated system) only increases and never decreases
• The standard mathematical form of the Second Law is ΔSsystem + ΔSsurroundings = ΔSuniverse, where ΔSuniverse > 0, showing that entropy can decrease within a system as long as there is an increase of equal or greater magnitude in the entropy of the surroundings of the system
• Relationship between free energy change (ΔG), enthalpy change (ΔH), and entropy change (ΔS)


  ΔG = ΔH - TΔS
• Gibbs free energy


  The maximum amount of energy a substance can contribute to a chemical transformation or reaction, equal to the sum of entropy and the product of temperature in a closed system
• Equilibrium constant


  The ratio of the concentration of products to the concentration of reactants, denoted as Keq
• Relationship between ΔG°, Keq, and the direction of chemical reaction

  ΔG° = -RTlnKeq, where a negative ΔG° indicates a spontaneous reaction and a positive ΔG° indicates a non-spontaneous reaction
• ATP


  Adenosine triphosphate, the most important energy-rich compound in a cell, with a concentration varying from 0.5 to 2.5 mg/mL of cell fluid
• ATP

  • Its structural feature important for energy release is the phosphoric acid anhydride, or pyrophosphate, linkage
  • The pyrophosphate bond is hydrolyzed when ATP is converted to adenosine diphosphate (ADP), releasing over 7 kcal/mol of energy
  • ATP is produced by processes that supply energy to the organism, and is hydrolyzed by processes that require energy, making it the principal medium of energy exchange in biological systems
• Other high-energy compounds besides ATP

  • Creatine phosphate
  • Phosphoenolpyruvate
  • 1,3-Bisphosphoglycerate