Lecture 13 9/30/05 Lecture Outline Cellular Respiration: 1. Regulation of Enzymes: competitive, allosteric, phosphorylation Harvesting Chemical Energy 2. Equilibrium 3. Digestion vs Metabolism: catabolism and anabolism Chapter 9 4. What is a metabolic pathway? 5. Feedback regulation of pathways 6. Catabolic pathways - stepping down the oxidation series of carbon 7. Harvesting energy from redox reactions I. General - substrate level phosphorylation ATP + Principles – reducing equivalent carriers NADH + H , FADH2 8. Example of a catabolic pathway: Fatty Acid Oxidation 1 2 Figure 9.1 Reactions that proceed in a closed system Living systems = Open System – Eventually reach equilibrium – Must have constant flow of materials in – Constant Energy Input Can do Cannot Do Useful ∆G < 0 ∆G = 0 work work Equilibrium to a living system is called…. ∆G < 0 (b) An open hydroelectric system. Flowing water keeps driving the generator because intake and outflow of water keep the system from reaching equlibrium. (a) A closed hydroelectric system. Water flowing downhill turns a turbine that drives a generator providing electricity to a light bulb, but only until the system reaches equilibrium. Figure 8.7 Figure 8.7 A 3 4 Metabolism – totality of all chemical Metabolism: a series of favorable reactions reactions of an organism Inputs ∆G < 0 digestion ∆G < 0 Hydrolysis of polymers to monomers ∆G < 0 No energy Harvested ! occurs “outside” the cell catabolism –energy capture reactions oxidize substrates, produce energy carriers Figure 8.7 Waste anabolism –energy utilizing reactions Metabolic Pathway: Products use energy carriers, build things 5 The product of each reaction becomes the reactant for a next, so6 Note: ∆G<0 no reaction reaches equilibrium Metabolic Pathway Chemistry of Life is organized Enzymes work in series into Metabolic Pathways Each enzyme carries out one reaction Reactions in series constitute a Pathway Enzyme 1 Enzyme 2 Enzyme 3 Enzyme 1 promotes reaction A B A B C D Reaction 1 Reaction 2 Reaction 3 Enzyme 2 promotes reaction B C Starting Product Enzyme 3 promotes reaction C D molecule Enzyme 4 promotes reaction D E A Enzyme 5 promotes reaction E F A F F Enzyme 6 promotes reaction F G B E A A F F So as long as have A, G will be produced C D Each reaction is facilitated by a different enzyme7 8 Initial substrate (threonine) Active site thr available Feedback Regulation Threonine in active site Enzyme 1 (threonine F Isoleucine deaminase) Product used up by A cell Of F F Intermediate A A Feedback Pathway Enzyme 2 inhibition Active site of B E enzyme 1 no Is longer binds A A threonine; Intermediate B F F pathway is Allosteric switched off C D Enzyme 3 “Plenty of Regulator Of Intermediate C F Isoleucine Enzyme 4 binds to over Here, First Enzyme allosteric site Shut it OFF!” In Pathway Intermediate D Enzymes can be regulated Enzyme 5 9 10 Allosteric modulator ? Figure 8.21 End product (isoleucine) ile Why so many steps in a pathway? 15 gallons Of gasoline For example, oxidation of glucose: Many Small Controlled C6H12O6 (glucose) + 6O2 6CO2 + 6H2O reactions ∆G= -686 kcal/mol ∆H = -673 kcal/mol T∆S= -13 kcal/mol in the cell, this is done in >21 steps! Capture the energy in small packets ie, 36 ATP units of 7.3 kcal 11 12 What is an OXIDATION? catabolic pathway For ionic species: Reduced means Oxidize in discrete steps “rich” in electrons Step down the oxidation series of carbon Oxidized means “fewer” electrons some activation step Fe++ Fe+++ oxidation step, with energy harvest reduced oxidized reorganization step Oxidation: loss of e- oxidation step, another harvest Organic Reductions Reduction : gain of e- + etc X + 2e- + 2H XH2 yield product of pathway Organic Oxidation 13 + 14 YH2 Y + 2e- +2H OXIDATION Highly series of carbon reduced Reduced = High enthalpy “few” bonds to oxygen Hydrocarbon chain R-CH=CH2 “many” bonds to hydrogen Unsaturated hydrocarbon Alcohol Ease of Removing Carbonyl electrons electronegativity Carboxylic Acid Oxidized “few” bonds to oxygen Carbon Dioxide “many” bonds to hydrogen 15 16 Highly oxidized Catabolic Pathways R-CH2 -CH 3 Progress down the Oxidation Series R-CH=CH2 Of Carbon In Metabolism: R-CH2-CH2 -OH Highly reduced fully oxidized “adding O” R-CH -C=O CH3-CH2-CH2-(CH2)x-CH2-C-O + O2 H2O + CO2 + energy 2 Fatty acid O (captured) H “H-H” removed Partially reduced fully oxidized R-CH2-C=O “H- + H+” removed OH + O2 H2O + CO2+ energy “2e- + H+ + H+” removed” carbohydrate (captured) 17 O=C=O 18 REDOX Reactions Carriers of Reducing Equivalents Oxidations always paired with reductions CoEnzymes (CoFactors) If one thing gets oxidized, NAD+ nicotinamide adenine dinucleotide another becomes reduced NAD+ + H+ + 2e- -> NADH Reactants Products becomes oxidized Change the degree NADP+ nicotinamide adenine dinucleotide phosphate CH + 2O CO + Energy + 2 H O 4 2 2 2 of electron sharing in covalent bonds NADP+ + H+ + 2e- -> NADPH H becomes reduced H H FAD flavin adenine dinucleotide H C H OOO C O O + H FAD + 2H + 2e- -> FADH2 Methane Oxygen Carbon dioxide Water (oxidizing (reducing Figure 9.3 agent) agent) 19 20 Electrons from organic compounds Are usually first transferred to NAD+, a coenzyme 2 e– + 2 H+ 2 e– + H+ NAD+ NADH H 2 e- O O H H + + 2 H + 2[H] Reduction of NAD C NH2 C NH2 + H+ (from food) Oxidation of NADH N+ N Nicotinamide Nicotinamide CH (reduced form) O 2 O (oxidized form) e- 1 e- OOP – 1 H+ O H H O P O– HO OH NH HO 2 O CH2 N N H NAD+ to NADH N N H O Carries 2e- and 1 H+ H H 21 22 HO OH Figure 9.4 NADP+ looks like this: FAD looks like this: + NADP+ NADPH H H+ 2e- 1 e- 1 e- 1 H+ 1 H+ 23 FAD to FADH2 24 Carries 2e- and 2 H+ How harvest energy packets upon oxidation? Carriers of Energy potential - high energy phosphate bonds ATP, GTP production substrate level phosphorylation less usual form of energy harvest -Carriers of reducing equivalents Oxidized form – reduced form NAD+ NADH + H+ FAD FADH 2 ATP – common energy -Can cash in reduced carriers for ATP currency “$$$” oxidative phosphorylation 25 26 High energy phosphate bonds Substrate Level Phosphorylation How harvest energy packets upon oxidation? Example: + + “A” NAD “B” NADH + H $$$ - high energy phosphate bonds Enzyme 1 = = O O = O= O ATP, GTP production R- C -C-OH P R- C-Pi C substrate level phosphorylation i = High Energy less usual form of energy harvest Compound O Oxidized to Poker chips Carbon Dioxide -Carriers of reducing equivalents Oxidized form – reduced form “B” NAD+ NADH + H+ (ATP) O= FAD FADH Enzyme 2 2 ADP -Pi “C” R- C-Pi + ADP-OH O= -Can cash in reduced carriers for ATP Energy of Oxidations “Captured” R- C27-OH oxidative phosphorylation 28 in the FORMATION of ATP Oxidized to ACID The Regeneration Energy Carriers Let’s put it together Energy carriers (ATP, NAD+, FAD) present in only minute amounts Step down oxidation series 2e- 2e- 2H+ Harvest energy in discrete packets 2H+ Cashed in Captured in catabolism NADH + H+ Fatty Acid Oxidation Pathway Energy from catabolism Energy for cellular work (exergonic, energy yielding (endergonic, energy- processes) consuming processes) NAD+ 29 30 Fatty Acid Oxidation (β-oxidation) Priming Start of Pathway Step Saturated hydrocarbon Priming Step (energy input) 2e- 2 H+ -steps down removed CH -CH -R-CH -CH -C=O ATP + CoA-SH oxidation Ester 3 2 2 2 (acid) Fatty acid O- states of carbon unsaturated hydrocarbon -captures Reducing potential NADH + H+ CH3-CH2-R-CH2-CH2-C=O ADP + Pi FADH Ketone 2 2e- Fatty acyl CoA alcohol S-CoA 31 2 H+ 32 removed Net Result of Fatty Acid Oxidation Pathway Summary Fatty acid shortened by 2 carbon unit • Digestion, Metabolism, Catabolism, Anabolism • Biochemical Pathway; feedback regulation • Catabolic Pathways 2 carbon acid attached to CoA (acetyl CoA) - Step down oxidation series of carbon - Harvest energy in discrete packets Oxidation of Carbon -CH - to –C=O 2 • ATP, NADH + H+, FADH to acid 2 S CoA • Fatty Acid Oxidation Pathway Capture reducing equivalents 2 NADH + H+ 2 FADH2 33 34.