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Energy and Life • Energy must be released from food gradually. • Energy must be stored in readily accessible forms. • Release of energy from storage must be finely controlled so that it is available exactly when and where it is needed. • Just enough energy must be released as heat to maintain constant body temperature. • Energy in a form other than heat must be available to drive chemical reactions that are not favorable at body temperatures. Pearson Prentice Hall 2007 Spontaneous reactions release free energy, which is available to do work. ∆G = ∆H – T∆S Exergonic applies to the release of free energy, represented by a negative ∆G. Exothermic applies to the release of heat, represented by a negative ∆H. Endergonic: A non-spontaneous reaction or process that absorbs free energy and has a positive ∆G. Free-energy change switches sign but keeps the same magnitude for the reverse of a reaction. Pearson Prentice Hall 2007 1 Graphical Representation of Exergonic/Endergonic In an unfavorable reaction, the products have more energy than the reactants. The opposite is true for a favorable one. Pearson Prentice Hall 2007 Together, all of the chemical reactions that take place in an organism constitute its metabolism. Metabolic pathways may be linear, cyclic, or spiral Pearson Prentice Hall 2007 2 Catabolism: Metabolic reaction pathways that break down food molecules and release biochemical energy. Anabolism: Metabolic reactions that build larger biological molecules from smaller pieces. Pearson Prentice Hall 2007 The Stages of Metabolism: Conversion of Food into Biochemical Energy 1.Digestion 2.Production of Acetyl-SCoA ( a common intermediate produced from breakdown of all classes of food, carbo, lipids and proteins). 3.Citric Acid Cycle 4. Electron Transport Chain and ATP synthesis Pearson Prentice Hall 2007 3 Pearson Prentice Hall 2007 Overview: Pathway Of Glucose to Acetyl-SCoA Through Pyruvate. We will look at the features of Glycolysis reactions separately….. Pearson Prentice Hall 2007 4 Metabolism of Triacylglycerols: TAG’s undergo hydrolysis to give Fatty acid and glycerol Fatty acids undergo ►Resynthesis of triacylglycerols for storage ►Conversion to acetyl-SCoA Catabolic pathways in brown And Anabolic pathways are shown In blue. We will look into overview of reactions of β-oxidation of fatty acids separately.. Pearson Prentice Hall 2007 Amino Acid pool: The entire collection of free amino acids in the body. Amino acids are continuously entering the pool, not only from digestion but also from the breakdown of old protein, and are continuously being withdrawn for synthesis of new nitrogen-containing biomolecules. Amino Acid metabolism is a complex pathway consisting of many different pathways. Pearson Prentice Hall 2007 5 Pearson Prentice Hall 2007 Catabolic intermediates produced from Amino Acids can enter the citric acid cycle in different stages of the cycle. What are Ketogenic and Glucogenic A.A’s? Pearson Prentice Hall 2007 6 The Citric Acid Cycle: a cyclic pathway of eight reactions. the details of this cycle separately…. Pearson Prentice Hall 2007 The Electron-Transport Chain & ATP synthesis •The electron transport system is a series of oxidation-reduction (redox) reactions that transfers electrons and hydrogen ion from one chemical complex to another. The series of reactions are exergonic. •Two agents that take part in this series are the coenzymes NAD+ and FAD. Both are nucleotide derivatives. •FAD stands for Flavin Adenine Dinucleotide. It is synthesized in our bodies from the vitamin Riboflavin. Its oxidized form is FAD and the reduced form is FADH2. •NAD stands for Nicotinamide Adenine Dinucleotide.It is synthesized in our bodies from the vitamin Niacin. The oxidized form is NAD+ and the reduced form is NADH. Pearson Prentice Hall 2007 7 Review: Redox reactions are loss/gain of electrons. OIL : Oxidation is Loss of electrons RIG: Reduction is Gain of electrons Pearson Prentice Hall 2007 Consider the following coupled redox reaction: -O O C + NAD + H C H C - OH H C H C -O O H C + NADH + H+ C O malate O O -O O oxaloacetate Two hydrogens and two electrons are removed from malate. NAD+ takes both electrons and one hydrogen (it is reduced). The other Hydrogen is without an electron and floating around as H+ This is an example of a biochemical redox reaction. Pearson Prentice Hall 2007 8 Later on in the Electron Transport Chain, NADH and H+ is going to transfer the two electron and the hydrogen ion to FAD Which becomes FADH2. This reaction releases energy. Write this equation. The NAD+ now regenerated is free to go back and pick up more electrons and Hydrogens. The FADH2 is ready to pass on its acquired electrons and Hydrogen ions to the next complex. The electron transport chain consists of enzymes in four complexes held in fixed positions and the two coenzymes that carry electrons from one complex to the next. Enzymes of the electron transport chain are imbedded in the inner membrane of mitochondria. Ultimately, water will be produced from these hydrogen and electron and The O2 we breathe in. Pearson Prentice Hall 2007 The ETC is an energetically downhill process.Each enzyme complex (I-IV) contains several enzyme carriers. The 5th complex contains ATP Synthase which is made up of a group of proteins which work together to make ATP. Final step is ATP production using energy released during the ETC. Note: Water is also being produced More than 90% of the oxygen we breathe is used in electron transport–ATP synthesis reactions. Pearson Prentice Hall 2007 9 Energy from three of the transfers is used to transport hydrogen ions across the inner mitochondrial membrane to the intermembrane Space. The maintenance of this concentration gradient across the membrane is crucial—it is the mechanism by which energy for ATP formation is made available. Pearson Prentice Hall 2007 Structures of Electron carriers in the ETC chain This is a partial structure of NAD+. The + sign comes from the quaternary N atom. In NADH a new C-H bond is formed. One H+ is floating around. Pearson Prentice Hall 2007 10 Structures of Electron carriers in the ETC chain FAD picks up two electrons and two H ions To form FADH2 Note the site of reduction. Pearson Prentice Hall 2007 Structures of Electron carriers in the ETC chain This molecule is also known as ubiquinone (two ketone groups). Note the sites of redox reaction. •Reminder: Electrons are passed from weaker to increasingly stronger oxidizing agents, with energy released at each transfer. Pearson Prentice Hall 2007 11 Other important electron acceptors are various cytochromes, which are proteins that contain heme groups in which the iron cycles between Fe+2 and Fe+3 and proteins with iron–sulfur groups in which the iron also cycles between Fe+2 and Fe+3 (only 1 e- transfer) Pearson Prentice Hall 2007 Suggested Homework for Metabolic Pathways: 21.41 – 21.44, 21.47, 21.49, 21.53 a,b, 21.54 a,b, 21.55, 21.67, 21.74 23.26, 23.27, 23.39, 23.43 and 23.44, 23.45, 23.47, 23.48 25.16, 25.19, 25.26, 25.30-25.36,25.39 (in class), 25.40, 25.42 Pearson Prentice Hall 2007 12 The purpose of coupling two biochemical reactions is to A) lower the activation energies of both reactions. B) convert an endergonic reaction to an exergonic one. C) convert an exergonic reaction to an endergonic one. D) use an endergonic reaction to drive an exergonic reaction. E) use an exergonic reaction to drive an endergonic reaction. Pearson Prentice Hall 2007 In the pathways for the digestion of food and the production of biochemical energy, the oxidation of AcetylSCoA occurs in: 1. stage 1: digestion. 2. stage 2: Acetyl-SCoA production. 3. stage 3: citric acid cycle. 4. stage 4: ATP production. Pearson Prentice Hall 2007 13 All of the following molecules are directly involved in the electron transport chain except A) coenzyme Q. B) ADP. C) cytochrome c. D) acetyl-SCoA. E) H2O. Pearson Prentice Hall 2007 14