Lectures 22 & 23 The TCA Cycle-BW

And now form a double bond tca cycle enzyme part of

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Unformatted text preview: a double bond. TCA cycle enzyme - part of complex 2 - the only TCA cycle enzyme that is membrane bound - part of complext two of elcetron trasnport chain - embedded the mithcondria. FAD bound to dehydrogenase becuase of this reaction - dones tcome on and off the enzyem. Accepting of electros - FADH doesn't come off the molecules - no diffusion of FADH2 away from the enzyme itself. indicate FAD being bound. Dehydrogenation FAD is covalently bound to the enzyme This enzyme is also part of the electron transport pathway in the inner mitochondrial membrane 4/6 and 4/8/13 MCB 2000 Lectures 22 & 23 FAD picks up e- one by one Accepts 1 elctrons at a time and added to central ring s tucutre. - form a semiquinone - very reactive - can undergo redox central. if the second elctrons dont follow the fi rst one - have a radial (radial damging to macromolecules) one reason why you want to keep FAD with this radical. 4/6 and 4/8/13 MCB 2000 Lectures 22 & 23 Fumarase Catalyzes the Trans-Hydration of Fumarate to Form L-Malate Hydration across the double bond Add water across double bond - last reaction matalte deodehydaase. 4/6 and 4/8/13 MCB 2000 Lectures 22 & 23 Malate Dehydrogenase Completes the Cycle by Oxidizing Malate to Oxaloacetate Unfavorable - but made possible by coupling. An NAD+-dependent oxidation This reaction is energetically expensive: Go' of +30 kJ/mol The equilibrium favors malate; [OAA] is very low. 4/6 and 4/8/13 MCB 2000 Lectures 22 & 23 What Are the Energetic Consequences of the TCA Cycle? One acetate through the cycle produces 2 CO2, 1 ATP (GTP), 4 reduced coenzymes: 3 NADH 1 FADH2 These numbers double when expressed per glucose molecule. for glucose - 2 acytl CoA - have to double them 4/6 and 4/8/13 MCB 2000 Lectures 22 & 23 Allosteric regulation only - no hormonal regulation. non undergo phosphorlyation or dephosohproyatlon. Intermediates - like ketone bodies enter the TCA cycle. TCA cycle is used by all nutrients (carbs, proteina nd fat) fee into the TCA cycle - operation all the time. the rate changes How Is the TCA Cycle Regulated? r ate dependent on energy chagrge. chemically linked to the electron transfer chain - TCA cycle going to slow down as well. energy charge for regulation of pahtway that genereate ATP Citrate synthase control by [OAA]eed ATP - TCA cycle goes faster. Citrate synthase (substrate) N c ondentation between 2 becuase FBI by [citrate]OAA is the rate liminted carbons acetyl coA. importantto citrate substrate - needs to coupled s ynthase Isocitrate dehydrogenase - rate-limiting Isocitrate-rate liminintg fi rst step step where you gnerate NADH. c hemical link between TCA ATP and NADH inhibit,cycle and the electron transport c hain. NADH donate elctrons to + activate c hain ADP and NAD -Ketoglutarate dehydrogenase FBI by NADH and succinyl-CoA Chemical mechanism idential (ketoglugrate and ATP inhibits pryvuate dehydrogenase) -require same vitamin c ofactor. Also note pyruvate dehydrogenase: ATP, NADH, acetyl-CoA inh...
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