Bioenergetics: Cell as a Chemical Factory Metabolism: All the chemical processes of the cell. Catabolic Pathways: sugars Produce energy CO 2 + H 2 O + release energy Anabolic pathways: Absorption of energy build amino acids (a.a.) A.A. Protein Nucleotides (NT) DNA or RNA hv Photosynthesis: CO 2 + H 2 O Sugars
Bioenergetics: All metabolic pathways are subject to the 1 st and 2 nd laws of thermodynamics 1 st : Energy can be transferred or transformed, but it can not be created or destroyed 2 nd : Every process in the universe increases Disorder (Entropy) Na + Na + Entropy Diffusion Diffusion
Bioenergetics: Chemical reactions in the cell All controlled, stepwise fashion Compartmentalized Requires enzymes (proteins) Serve as a catalyst can be re-used Increase entropy Increase rate of the reaction (rxn) Chemical RXNs Spontaneous: Non-Spontaneous: ΔG = Gibbs free energy Free energy of a reaction: difference between the final state and the initial state
ΔG = ΔH TΔS ΔG = Gibbs free energy amount of energy that is capable of doing work during a reaction at constant pressure and constant temperature. When a system changes to possess less energy (free energy is lost) than the free energy change (ΔG) is negative and the reaction is exergonic (spontaneous) Enthalpy: the heat content of a system (H). When a chemical reaction releases heat it is exothermic and has a negative (ΔH). Entropy: Randomness or disorder of a system. When the products of a reaction are less complexed and more disordered than the reactants, the reaction proceeds with a gain in entropy (ΔS).
Bioenergetics: ΔG = Gibbs free energy Free energy of a reaction from the final state and the initial state ΔG ΔH : free energy (amount of energy that can do work) : Enthalphy (heat) ΔH < 0 ΔH > 0 T - temp ΔS Entropy ΔS < 0 ΔS > 0 : constant
Bioenergetic: Enthalpy and Entropy ΔG = ΔH TΔS constant ΔG < 0 Will be spontaneous because: Give up enthalphy (H decreases) Give up order (S increases) 1 or both have to happen for a reaction to be spontaneous ΔG = ΔH TΔS ΔG = ΔH TΔS ΔG = ΔH TΔS
Bioenergetics: Chemical Equilibrium and Metabolism reactant A Reversible! product B Cells live in an open system! Cell: OPEN system Every rxn in the cell is potentially Reversible! In a closed system: reach equilibrium ΔG = 0 Environment Matter Energy Cells are an open system: Metabolism never reaches equilibrium Defining feature!!!
Bioenergetics: ΔG = Gibbs free energy ΔG = Gibbs free energy Made Easy! Bond Energy* It takes energy to break chemical bonds Energy is released as chemical bonds form Many forms of energy Electrical Mechanical Chemical All forms are ultimately converted into heat therefore biologist measure energy in unit of heat: Kilocalorie (kcal) amount of heat to warm 1 liter of water 1 C 2H 2 O 2H 2 + 0 2 440 kcal consumed when 4 (0-H bonds) are broken 322 kcal released when form 2(H-H) and 1 (O-O) bond Where is the energy gone? *Note: also see: http://www.biologypages.info/b/bondenergy.html
Bioenergetics: ΔG = Gibbs free energy Made Easy! 04-07-16: Lecture 4 2H 2 O 2H 2 + 0 2 440 kcal 322 kcal (consumed) (released) It is now Chemical Energy stored in the bonds of 2H 2 + 0 2. This is called free energy. ΔG = BEreactants BEprodcuts ΔG = 440 kcal - 322 kcal = 118 kcal ΔG = + 118 kcal we ve added 118 kcal to the chemical system.
Bioenergetics: ΔG = Gibbs free energy Made Easy! 04-07-16: Lecture 4 2H 2 + 0 2 2H 2 0 322 kcal 440 kcal (consumed) (released) ΔG = BEreactants BEprodcuts So ΔG = 322 kcal 440 kcal = -118 kcal ΔG = - 118 kcal : we ve lost 118 kcal from the chemical system.
Bioenergetics: ΔG = Gibbs free energy Made Easy! 04-07-16: Lecture 4 Where did this free energy go: ΔG = BEreactants BEprodcuts But heat does us no good if we can t use it! Cells have solved a way to oxidized molecules and harvest the free energy loss Cellular Respiration C 6 H 12 O 6 + 60 2 6CO 2 + 6H 2 O ; ΔG = -686 kcal 2878 kcal 3564 kcal (consumed) (released) Photosynthesis 6CO 2 + 6H 2 O C 6 H 12 O 6 3564 kcal 2878 kcal (consumed) (released) + 60 2 ; ΔG = +686 kcal ΔG < 0 (spontaneous) ΔG = ΔH TΔS ΔG > 0 (non spontaneous) ΔG = ΔH TΔS
Bioenergetics: ΔG = Gibbs free energy Made Easy! 04-07-16: Lecture 4 Cellular Respiration C 6 H 12 O 6 + 60 2 6CO 2 + 6H 2 O ; ΔG = -686 kcal Breakdown (oxidizing) glucose C 6 H 12 O 6 + 60 2 Free Energy (ΔG) Course of rxn 6CO 2 + 6H 2 O ΔG = -686 kcal exergonic Lost as heat Oxidation of glucose is highly controlled stepwise fashion; compartmentalized to maximize ability to recoup some of the lost free energy in the form of:
Release Released Consume Bioenergetics: ΔG = Gibbs free energy Made Even Easier! Cellular Respiration C6H12O6 + 602 6CO2 + 6H2O ; ΔG = -686 kcal 04-07-16: Lecture 4 2878 kcal 3564 kcal (consumed) (released) Need to release 2878 kcal to balance amount consumed 2878 kcal Free Energy (ΔG) 0 Free energy lost 3564 kcal ΔH But actually 3564 kcal released Course of rxn To balance equation ΔG = ΔH TΔS Lose heat from chemical system to environment
Bioenergetics: ΔG = Gibbs free energy Made Easy! 04-07-16: Lecture 4 Photosynthesis Synthesis of glucose 6CO 2 + 6H 2 O C 6 H 12 O 6 + 60 2 ; ΔG = +686 kcal C 6 H 12 O 6 + 60 2 Free Energy (ΔG) ΔG = +686 kcal endergonic Added : able to do work 6CO 2 + 6H 2 O Course of rxn The conversion of CO2 + H2O glucose is strongly endergonic would never happen without the environment (photosynthesis). So how do endergonic reactions take place in the cell? ATP!
Release Released Consume Bioenergetics: ΔG = Gibbs free energy Made Even Easier! Photosynthesis 6CO 2 + 6H 2 O C 6 H 12 O 6 + 60 2 ; ΔG = +686 kcal 04-07-16: Lecture 4 3564 kcal 2878 kcal (consumed) (released) 3564 kcal But actually release only 2878 kcal Free Energy (ΔG) 0 ΔH Heat infused Free energy gain 3564 kcal Need to release 3564 kcal to balance amount consumed Course of rxn To balance equation ΔG = ΔH TΔS
Bioenergetics: Enzymes (E) speed up reactions reactant product reactant product A B A B Enzymes ΔG < 0 ΔG > 0 Increase rate of the reaction (rxn) Serve as a catalyst can be reused Allows for the influx of energy Reactant-Enzyme Transitional State A + E [A E] B + E Enzyme is recycled
reactant A reactants product B reactant A product B products Free Energy (ΔG) Free Energy (ΔG) products reactants Course of rxn Course of rxn
Bioenergetic: Reactions inside a living cell reactant A ΔG < 0 product B A E Transitional state Energy of activation reactants E a Energy of activation With enzyme Free Energy (ΔG) A + E ΔG B + E products Course of rxn G < 0 so the reactions looks spontaneous but actually requires and enzyme!
Free Energy (ΔG) reactants reactants 04-07-16: Lecture 4 Bioenergetic: Reactions inside a living cell ΔG < 0 Exergonic ΔG > 0 Endergonic Enzymes (E): Speeds up rxn Lowers Energy of activation (Ea) G is unchanged Works for forward and reverse rxns products products Chemistry takes place here Course of rxn Course of rxn Reactant-Enzyme Transitional State Product-Enzyme Transitional State A + E [A E] [B E] B + E Enzyme is recycled
Bioenergetic: Enzymes are substrate specific (SPECIFICITY) There can be > 1 in a reactions. Substrate is acted on by the enzyme. Basic Properties of Enzyme Active Site: pocket on enzyme where substrate can bind Specificity: compatible fit between enzyme and substrate (remember R-groups - chemical toolbox) Induced Fit: substrate binding induces 3D structural change of Enzyme Chemistry takes place with reactants (transitional states)
Catalytic cycle of an Enzymes (Reactant) Sucrose Sucrase(E) Glucose (products) + Fructose 1 molecule 2 molecules E + Sucrose + H20 [E S H20] E + Glucose + Fructose Binding at active site Bound complex Induced fit Chemistry Break bonds