Bioenegertics

• Bioenergetics


  The degradation of fuel resulting in the production of heat and chemical energy, which is either used instantaneously or stored in a usable form
• Bioenergetics is the quantitative study of energy relationships and energy conversion in biological systems
• Bioenergetics


  The study of the energy changes accompanying biochemical reactions
• Biologic systems are essentially isothermic and use chemical energy to power living processes
• The way in which an animal obtains suitable fuel from its food to provide this energy is basic to the understanding of normal nutrition and metabolism
• Death from starvation occurs when available energy reserves are depleted, and certain forms of malnutrition are associated with energy imbalance (marasmus)
• Thyroid hormones control the metabolic rate (rate of energy release), and disease results if they malfunction
• Excess storage of surplus energy causes obesity, an increasingly common disease of Western society which predisposes to many diseases, including cardiovascular disease and diabetes mellitus type 2, and lowers life expectancy
• Obesity


  A disorder involving excessive body fat that increases the risk of health problems
• Obesity


  • Often results from taking in more calories than are burned by exercise and normal daily activities
  • Occurs when a person's body mass index is 30 or greater
  • The main symptom is excessive body fat, which increases the risk of serious health problems
  • The mainstay of treatment is lifestyle changes such as diet and exercise
• Free energy

  The useful energy in a system
• Gibbs change in free energy (ΔG)

  That portion of the total energy change in a system that is available for doing work—that is, the useful energy, also known as the chemical potential

  
• First law of thermodynamics

  • The total energy of a system, including its surroundings, remains constant
  • Energy may be transferred from one part of the system to another, or may be transformed into another form of energy
• Second law of thermodynamics

  • The total entropy of a system must increase if a process is to occur spontaneously
  • Entropy is the extent of disorder or randomness of the system and becomes maximum as equilibrium is approached
• If ΔG is negative


  The reaction proceeds spontaneously with loss of free energy, that is, it is exergonic
• If ΔG is positive


  The reaction proceeds only if free energy can be gained, that is, it is endergonic

  
• If ΔG is zero

  The system is at equilibrium and no net change takes place
• The standard free-energy change at a standard state of pH 7.0 is denoted by ΔG0′

  
• The actual ΔG may be larger or smaller than ΔG0′ depending on the concentrations of the various reactants, including the solvent, various ions, and proteins
• An enzyme only speeds up the attainment of equilibrium; it never alters the final concentrations of the reactants at equilibrium
• Endergonic processes


  • Proceed by coupling to exergonic processes

  
• The vital processes—for example, synthetic reactions, muscular contraction, nerve impulse conduction, and active transport—obtain energy by chemical linkage, or coupling, to oxidative reactions

  
• The conversion of metabolite A to metabolite B occurs with release of free energy


  It is coupled to another reaction in which free energy is required to convert metabolite C to metabolite D
• Exergonic


  Processes accompanied by loss of free energy
• Endergonic


  Processes accompanied by gain of free energy
• Catabolism


  The breakdown or oxidation of fuel molecules
• Anabolism


  Synthetic reactions that build up substances
• Metabolism


  The combined catabolic and anabolic processes
• An endergonic process cannot exist independently, but must be a component of a coupled exergonic–endergonic system where the overall net change is exergonic

  
• Coupled reactions


  1. Exergonic reaction

  2. Endergonic reaction

  
• Exergonic


  Process accompanied by loss of free energy
• Endergonic


  Process accompanied by gain of free energy
• Endergonic processes cannot exist independently, but must be a component of a coupled exergonic-endergonic system where the overall net change is exergonic
• Coupling mechanism


  Common obligatory intermediate (I) takes part in both reactions
• Coupling allows the rate of utilization of the product of the synthetic path (D) to determine by mass action the rate at which A is oxidized
• Coupling provides a basis for respiratory control, the process that prevents an organism from burning out of control
• Dehydrogenation-hydrogenation coupling


  Dehydrogenation reactions coupled to hydrogenations by an intermediate carrier

  
• Alternative coupling mechanism


  Synthesize a compound of high-energy potential in the exergonic reaction and incorporate this into the endergonic reaction

  
• Autotrophic organisms utilize simple exergonic processes like energy of sunlight or Fe2+ to Fe3+ reaction
• Heterotrophic organisms obtain free energy by coupling their metabolism to the breakdown of complex organic molecules