Bioenergetics BR17320 Biological Chemistry Lecture PDF

BR17320 Biological Chemistry Bioenergetics Prof Mike Threadgill [email protected] What is bioenergetics? Laws of thermodynamics...

BR17320 Biological Chemistry Bioenergetics Prof Mike Threadgill [email protected] What is bioenergetics? Laws of thermodynamics Energy & entropy Biochemical energy This lecture may be recorded. If so, your voice may be captured if you ask questions or respond during the lecture. Bioenergetics All processes in all cells in all of the millions of different species of organisms in the biosphere involve energy. Organisms require energy to live, grow and reproduce. They also need energy to take up nutrients from their environment and to dispose of waste. Ultimately, all energy for living organisms on Earth derives from the Sun. p+ p+ p+ p+ 2  hn Core 2  e+ temperature 2n 1.4  107 C E = mc2 Bioenergetics hn Photosynthesis in plants, algae, bacteria O2 & reduced CO2 biochemicals Respiration in animals, plants, algae, bacteria heat  Thermodynamics “Movement of Heat” First Law of Thermodynamics Energy is neither created nor destroyed during any physical or chemical process but it may undergo change from one form to another Conservation of energy Perpetual motion machines are impossible Second Law of Thermodynamics All physical and chemical changes tend to proceed in the direction which leads to increasing disorder The disorder (entropy) of the Universe is always increasing This means that no conversion of energy from one form to another can be 100% efficient; there is always some loss of energy into non-useful forms  Thermodynamics Third Law of Thermodynamics As the temperature of a system approaches absolute zero (0 K), all processes cease and the entropy of the system approaches a minimum value This isn’t very relevant to biological systems Zeroth Law of Thermodynamics If two systems are each in thermal equilibrium with a third, they are also in thermal equilibrium with each other Very relevant to measurements in biological systems Bioenergetics The Laws of Thermodynamics apply to biological systems, including whole organisms Living cells are chemical engines operating (for mammals) at constant temperature The energy needs of most organisms are provided by solar energy, either directly or indirectly (with some exceptions) The flow of electrons in redox reactions drive energy transductions in living cells Living organisms are interdependent and exchange energy (and matter) through their environment; whole systems must be considered Bioenergetics Potential energy Nutrients in the environment Sunlight Chemical transformations in cells Chemical synthesis Energy transductionsMechanical work Osmotic & electrical gradients Production of light Transfer of genetic information Heat Increased entropy of surroundings Metabolism of nutrients produces simpler compounds which are excreted e.g. CO2, NH3, H2O, HPO42- Decreased entropy of the cell Polymerisation of monomers to form information-rich macromolecules e.g. DNA, RNA, proteins Biochemical energy Cytosol Respiratory O2 electron- H2O H+ H+ H+ H+ transport Mitochondrio chain H+ n ADP + Pi H+ ATP H+ Mitochondrial ATP H H H H+ + + + synthase H+ matrix Inner mitochondrial membrane Outer mitochondrial membrane  Biochemical energy H2O O - O - HO P O - HO P O - - O O O HO P O - H2N O P O - H2N O O O P O N N O P O N N Respiration O N O N N N O O Use of energy HO OH HO OH Phosphate (Pi) Adenosine diphosphate (ADP) Adenosine triphosphate (ATP) ATP is a major “energy currency” in the cell Biochemical energy Sodium potassium ATPase K+ K+ Na K ATPase ATP ADP + Pi Na+ Cytosol Na+ Na+ Cell membrane Biochemical energy Ion gradients drive many functions of the cell Proton gradients Bacterial flagellar rotation Active transport of other ions Production of heat Na+ and K+ gradients Bioluminescence Vision Muscular activity Neuronal activity Transport of other ions and molecules Biochemical energy Free energy Energy available to do useful work in the cell Free energy  enthalphy Useful concept in biochemistry, as it measures the energy available to carry out biochemical reactions, including coupled reactions Thermodynamic quantity that shows whether or not a reaction will occur under specific circumstances Related to the equilibrium constant Expressed as G (total free energy) or, more usually, as DG (change in free energy) kforward A+ C+ B kbackward D Equilibrium constant K = kforward/kbackward J. Willard Gibbs DG = DH - TDS Biochemical energy Free energy, enthalphy and entropy DG = DH - TDS DG = Change in Gibbs Free Energy DH = Change in enthalpy T = Absolute temperature (in Kelvin) DS = Change in entropy DG > Non-spontaneous reaction (endergonic reaction) 0 DG = Neither direction prevails (equilibrium) 0 DG < Spontaneous reaction (exergonic reaction) 0 DG < Implies that DS > 0 0 Biochemical energy Free energy A B DG RT ln([B]P/[A]P— ) RT ln([B]eq/[A]eq) = Term describing Term describing non-equilibrium reaction at reaction equilibrium R Ideal (general) gas constant) = 8.314 J mol-1 K-1 T Temperature (K) [A]P & Prevailing concentrations (kept constant) [B] [A]Peq & [B]eq Concentrations at equilibrium K = kforward/kbackward = [B]eq / [Aeq] DG RT ln([B]P/[A]P— ) RT ln(K) = Units of DG J mol-1 Biochemical energy Standard Free Energy Change DG0 DG0 is the change in free energy under standard conditions, which are: The concentration of ALL reactants and products is kept constant at 1.00 M (including water if it is a reagent or product) If a gas is involved, then it is kept at the constant partial pressure of 1.00 atmosphere ( = 101.3 KPa) The temperature is constant at 25C (T = 298.15 K) A B DG0 =0 RT ln(1/1) ln([B]P/[A]— P) RT ln(K) Under standard = conditions Biochemical energy The problem with DG0 DG0 is not very useful in biochemistry because H+ is involved in many enzyme- catalysed processes DG0 requires ALL components to be at 1.00 M concentration [H+] = 1.00 M implies pH = 0 ! However, most enzymes are inactive at pH = 0 DG0’ is used by biochemists as a more useful quantity DG0’ is the change in free energy when all conditions are standard except that pH = 7.00 DG0’ =— RT ln(K) At pH 7.00 DG =DG0’ + RT ln([B]p/[A]p) At pH 7.00 A reaction whose DG0’ is positive may still proceed if the steady-state ratio of [Products]/[Reactants] gives negative DG Biochemical energy - - O O HO P O - HO P O - - O O O HO P O - H2N O P O - H2N O O O P O N N O P O N N O N O N N N O O Use of energy HO OH HO OH Phosphate (Pi) Adenosine diphosphate (ADP) Adenosine triphosphate (ATP) DG0’ of hydrolysing the red bond is -31 KJ mol-1 but this refers to 1.0 M concentration of reactant and products Living cells have the relevant concentrations around 1 mM (e.g. frog skeletal muscle [ATP] = 8.5 mM; [ADP] = 0.25 mM; [Pi] = 2.6 mM) Biochemical energy Phosphate (Pi) Adenosine diphosphate (ADP) H2O Adenosine triphosphate (ATP) DG0’ of hydrolysing the red bond is -31 KJ mol-1 but this refers to 1.0 M concentration of reactant and products Living cells have the relevant concentrations around 1 mM (e.g. frog skeletal muscle [ATP] = 8.5 mM; [ADP] = 0.25 mM; [Pi] = 2.6 mM) [H2O] is essentially constant and changes can be ignored DG = DG0’ + RT ln([ADP][Pi]/[ATP]) DG =- DG0’ + RT ln([ADP][P 8.314 i]/[ATP]  298  2.303  log10{(2.5  10-4  2.6  10-3)/(8.5  10-3)} KJ 31 mol-1 -1 DG = -55 KJ mol The actual free energy for hydrolysing ATP to ADP in skeletal muscle is about 76% greater than DG0’ [ATP], [ADP] and [Pi] vary between tissue; therefore, the useful DG will also vary between tissues Biochemical energy Glucokinase O - HO P O - O O P O - H2N O OH O P O N N O O N HO N HO OH O OH HO OH Glucose ATP - O - HO P O O HO P O - H2N O O O P O N N O O N HO N HO OH O OH HO OH Glucose-6-phosphate ADP Biochemical energy Glucokinase Part reaction 2 Overall ATP ADP + Pi reaction Glucose + Glucose-6-phosphate + ATP ADP Gibbs Free Energy G Part reaction 1 Glucose + Pi Glucose-6- phosphate DG2 DGoverall DG1 DGoverall = DG1 + DG2 Reaction coordinate Biochemical energy Activation energy & rate of reaction Overall k = A e(-DGactivation / RT) reaction Glucose + Glucose-6-phosphate + ATP k = Rate constant ADP A = Pre-exponential factor Gibbs Free Energy G R = Ideal (general) gas constant DGactivation T = Temperature (Kelvin) DGoverall S. A. Reaction coordinate Arrhenius BR17320 Molecular Biochemistry Bioenergetics Prof Mike Threadgill [email protected] [email protected] What is bioenergetics? Laws of thermodynamics Energy & entropy Biochemical energy