verview of Metabolism and Bioenergetics! Wichit Suthammarak Department of Biochemistry, Faculty of Medicine Siriraj Hospital -- July 30 th, 2014! Metabolism Chemical transformation! Cell or organism! A series of enzyme-catalyzed reactions! Metabolic pathway! Substrates/reactants! Metabolic intermediates/metabolites! roducts! Enzyme- catalyzed reactions Slowly release/use of energy! Metabolic regulation!
Introduction to Metabolism! Catabolism vs Anabolism! Catabolism Degradative (organic nutrients to simple end Energycontaining nutrients Carbohydrates Fats roteins Cell macromolecules roteins olysaccharides Lipids Nucleic acids Anabolism Synthetic (small precursors to larger and products)! more complex Energy-yielding reactions! AD NAD() + FAD molecules)! Energy-consuming reactions! AT NAD()H FADH 2 Biological energy AT! Reducing equivalent: NAD()H, FADH 2!
1 st : Energy is Conserved! Energy can be neither created or destroyed! 2 nd : Increased Disorder! Any closed system will go spontaneously in one direction only toward increasing its entropy! (a) The first law of thermodynamics applied to metabolism. Heat transferred out of the body (Q) and work done by the body (W) remove internal energy, while food intake replaces it. (b) lants convert part of the radiant heat transfer in sunlight to stored chemical energy, a process called photosynthesis.! Source: boundless!
Types of system in thermodynamics! Surroundings Isolated system (universe) Closed system pen system H: enthalpy! m: mass!
Gibbs free-energy (G) vs Gibbs free-energy change (ΔG)! G = H - TS! G; Gibbs free-energy" " "H; enthalpy T; temperature " " " "S; entropy! ในความเป นจร ง reacting system จะเก ดการเปล ยนแปลงอย ตลอดเวลา ซ ง driving force ท ทำให เก ดการเปล ยนแปลงของ reacting system! จากภาวะหน งไปส อ กภาวะหน งค อ ΔG! ΔG = ΔH TΔS! ΔG = G final G initial!
Exergonic vs Endergonic reactions!
Equilibrium! aa + bb cc + dd! Equilibrium state Rate of forward reaction = rate of reverse reaction! Gibbs energy is at a minimum! In living cells, equilibrium is never attained! Metabolism is never at equilibrium! [Ion] across the membrane stays far from equilibrium! Equilibrium constant [C] K eq = c [D] d!! [A] a [B] b! > 1; favors product; negative ΔG! < 1; favors substrate; positive ΔG!
Standard Gibbs free-energy change (ΔG )! S! Start! [S] = 1M! [] = 1M! ΔG! 25 C (298 K)! Equilibrium! [S] = x M! [] = y M! ΔG is the amount of energy that causes the reacting system at the! standard state condition: [S] initial = [] initial = 1M, 25 C reach equilibrium! ΔG = RT ln K eq! R ค อ gas constant ม ค า 8.315 J/mol K! T ค อ absolute temperature ม ค า 298 K (273 + 25)!
Exergonic vs Endergonic reactions! [G6]! G1 G6! K eq =! [G1]! Start! [G1] = 1M! [G6] = 1M! ΔG! 25 C (298 K)! Equilibrium! [G1] = 0.1 M! [G6] = 1.9 M! ΔG = RT ln K eq! ΔG of G1 G6 = -(8.315 J/mol K)(298) ln (1.9/0.1)! " " " " = -7.3 kj/mol!
Conventional standard state condition Temp = 25 C! [substrate] initial [product] initial! = 1M! Biological standard state condition Temp = 25 C! [substrate] initial [product] initial! = 1M! Exception from standard state! [H + ] = 10-7 M (ph 7)! [H 2 ] = 55.5 M! [Mg 2+ ] = 1 mm!
Standard biological Gibbs free-energy change (ΔG )! S! Start! [S] = 1M! [] = 1M! ΔG! 25 C (298 K)! ph 7! Equilibrium! [S] = x M! [] = y M! ΔG = RT ln K eq! K eq ค อ equilibrium constant ท 25 C, ph 7!
LIFE = Displacement from Equilibrium S! Gibbs energy (G) URE S! URE! 0.01 0.1 1 10 100 bserved mass action ratio [ ]/[S ] obs obs Equilibrium mass action ratio [ ]/[S ] eq eq
Total standard Gibbs free-energy change! In sequential reactions, ΔG is additive! ΔG total = ΔG 1 + ΔG 2 +...! A B! ΔG 1! Sum:! B C! A C! ΔG 2! ΔG 1 + ΔG 2!
Total standard Gibbs free-energy change! In sequential reactions, ΔG is additive! Example the synthesis of glucose-6-phosphate (G6) from glucose! hosphorylation of glucose! Glucose + i G6 + H 2! ΔG = 13.8 kj/mol! AT hydrolysis! AT + H 2 AD + i! ΔG = -30.5 kj/mol! Sum: Glucose + AT G6 + AD! ΔG = 13.8 + (-30.5)! = -16.7 kj/mol!
Coupling reactions! Two or more reactions in a cell sometimes can be coupled! in order to drive the overall process in a favorable direction! Glucose + i G6 + H 2! ΔG = 13.8 kj/mol! thermodynamically! unfavorable! AT + H 2 AD + i! ΔG = -30.5 kj/mol! thermodynamically! favorable! Glucose + AT G6 + AD! ΔG = -16.7 kj/mol! thermodynamically! favorable!
High-Energy Compounds! AT- structure! hosphoester bond CH 2 Adenine H H H H AT AD + i " " "ΔG = -30.5 kj/mol (β-γ bond)! AD AM + i " " "ΔG = -45.6 kj/mol (α-β bond)! H hosphoanhydride bond Adenosine triphosphate (AT) H AM adenosine + i " "ΔG = -14.2 kj/mol!
High-Energy Compounds! How does AT hydrolysis release energy?! H : H Ribose Adenine AT hydrolysis AT 4- + H i H Ribose Adenine 3 H + AD 2- ionization resonance stabilization H + + Ribose Adenine AD 3- Resonance stabilization of inorganic phosphate (i)! Relief of charge repulsion!
High-Energy Compounds! Actual free-energy of AT hydrolysis! Question: Calculate the actual free-energy of hydrolysis of AT in human erythrocytes. ΔG of AT hydrolysis is -30.5 kj/mol, and [AT], [AD] and [i] in erythrocytes are 2.25 mm, 0.25 mm and 1.65 mm, respectively. Assume that the ph is 7.0 and the temperature is 37 C.! Solution: The actual free energy of AT hydrolysis under the given condition can be calculated by the following relationship! ΔG actual = ΔG + RT ln! [AD][i]! [AT]! = -30.5 kj/mol + [(8.315 J/mol K)(310 K) ln! (0.25 x 10-3 )(1.65 x 10-3 )! (2.25 x 10-3 )! = -52 kj/mol!
Summary! Gibbs free-energy (G)! G = H TS! Gibbs free-energy change (ΔG)! ΔG = ΔH TΔS, ΔG = G final G initial! Standard Gibbs free-energy change (ΔG )! ΔG = -RT ln K eq ; [S] int l = [] int l = 1M, 25 C! Standard biological Gibbs free-energy change (ΔG )! ΔG = -RT ln K eq ; [S] int l = [] int l = 1M, 25 C, ph 7! Actual Gibbs free-energy change (ΔG)! ΔG = ΔG + RT ln K ; [S] int l and [] int l = any, temp = any, ph7, new K eq!
High-Energy Compounds! Hydrolysis of phosphocreatine! H N C + NH 2 C CH 2 N CH 3 H 2 + NH 2 C CH 2 H 2 N H2N C N CH 3 C H N CH 2 N 2 + + i hosphocreatine Creatine resonance stabilization + C CH 3 hosphocreatine 2- + H 2 creatine + i 2- ; ΔG = -43.0 kj/mol! Instant source of energy in muscle during anaerobic condition! Creatine AT AT AD AD hosphocreatine During muscle exertion- Cr directly transfers phosphate group to AD to generate AT! At rest- Cr is generated by phosphorylation of Cr by AT!
High-Energy Compounds! Hydrolysis of phosphoenolpyruvate! C C H 2 i C C H tautomerization C C CH 2 hosphoenolpyruvate 3- (E ) CH 2 yruvate (enol form) CH 3 yruvate (keto form) E 3- + H 2 pyruvate - + i 2- ; ΔG = -61.9 kj/mol Tautomerization! Isomerization! Migration of H + accompanied by a switch of a single bond and an adjacent double band!
High-Energy Compounds! Ranking of biological phosphate compounds by ΔG hydrolysis!
Energy Extraction and Utilization! Direction of electron transfer! reparation for entry into the Krebs cycle! Removal of energized electrons! AT synthesis: oxidative phosphorylation!