Session 10: TCA Cycle Storyboard

These went to Think retrosynthetically G NADH NAD A Respiration: -- Mitochondrial reactions -- Require O2 (or another e acceptor) -- We can metabolize carbohydrates anaerobically or aerobically -- We can only metabolize lipids aerobically H CO2 H C OH C H 2C OP CH 3 Complex V IMS (inner membane space) Cytoplasm TCA, PDH, FA oxidation, urea cycle Energy AcCoA C OA Glycolysis FA Oxidation (later) IC CO2 αKG M F AcCoA (C2) * Reaction mechanism is strikingly similar to αKGDH (below). S CO2 SCoA The Chemistry 3 NADH @ 3 ATP/NADH 1 FADH 2 @ 2 ATP/FADH2 Markers O H 2C H 2C CO2 CO2 H 2C O C HO C H 2C SCoA HSCoA CO2 CO2 C SCoA H H 2C C O B C CS O H SCoA Claisen Reaction 2 CO2 TCA (Krebs) Cycle (8 Steps) D Carbanion Citrate Synthase CS is stereospecific. AcCoA attacks from top (Si) face only. More detail on this later. citrate (C6) OA (C4) oxaloacetate Pyruvate (P) S FAD Products a.) Acetyl CoA b.) NADH (E1 E2 E3) and reduce FAD FADH 2. Then, in a redoxchallenged last step, FADH 2 gives its electrons to NAD to yield NADH. The NADH is oxidized by the electron transfer chain (later.) ATP C 2. TCA Cycle - Overview -- receives Acetyl CoA from PDH E1 E2 E3 CO2 Basically, the pair of electrons move left to right across PDH ATP synthesis Oxidation of FADH 2 and NADH S S CH 3 Matrix e transport HSCoA C B Lipoic acid N C NADH Toxicity of AsO33 S S CO2 O CO2 + ATP/GTP + NADH + FADH 2 3. Electron transport and oxidative phosphorylation NAD H AcCoA + NADH 2. TCA: AcCoA O 1. PDH * Inner Membrane very porous 1 7 Harvesting of these e Outer membrane Stages: via PDH C Introducing: The Mitochondrion Oxidative metabolism of all metabolic fuels (carbohyrates, fats) via Acetyl CoA 1. PDH: P O HO H 2O B H 2C CO2 C CO2 H 2C CO2 1 GTP ~ 1 ATP Oxaloacetate (OA) Note: The cycle is catalytic - 2 carbons go in; 2 carbons go out; the [intermediates] do not change - they are the "catalysts" 12 ATP per C2 of AcCoA oxidized One micro-molar concentation very precious! Citroyl CoA Unstable! ΔG o = -31 KJ/mol Citrate (C) A Session 10 from AcCoA H 2C CS CO2 HO C CO2 H C CO2 B 1 8 Isocitrate Dehydrogenase Ac H 2C CO2 HC CO2 C CO2 * HO water removed and re-added CO2 O H 2C ICDH HC NAD O unstable (a β-keto acid) H 2C * See next page on stereochemical loss of CO2 is typically irreversible O C* O H 2C C * Pi HSCoA SCoA O GDP (ADP) GTP (ATP) Succinyl CoA 2 H 2C 2 CO2 H 2C 2 CO2 2 Succinate SDH H 2 CO2 2 C C FAD FADH 2 * HSCoA CO2 CO2 O2C 2 Glutamic Acid (E) αKGDH very similar to PDH Asp (D) Fumarase H 2O H MDH B HO NAD H C CO2 HC H CO2 NADH 2 C 2 CO2 H 2C CO2 O 2 2 Malate Fumarate OA Note trans isomer -- Thio-ester attacked by phosphate -- Look at GAPDH chemistry! -- Substrate-level phosphorylation symmetrical compound H C O2C C H Cylce starts again Bound to SDH H CO2 H -- which is embedded in mitochondrial inner membrane -- SDH also known as Complex II NADH more later αKG looks like pyruvate with an acetate "decoration" Malate Dehydrogenase Succinyl CoA synthetase CO2 C αKGDH H αKeto Glutarate Label ( & ) becomes scrambled! Because the molecule is symmetrical and SDH cannot tell the two ends apart. H 2C C CO2 PLP CO2 CO2 B CO2 HCH ( Ac ) H O C oxalosuccinate IC (Iso-citrate) Aconitase ICDH CO2 from OA - Ac works only on the bottom part of citrate (the "Pro-R" Arm) specificity of H 2C C NADH H H αKeto Glutarate Dehydrogenase Succinate Dehydrogenase Next AcCoA 2 A Detail on Stereochemical Specificity of 1 9 Aconitase -- The hydroxyl group always moves to the ProR arm and never to the ProS, even though they are chemically identical, because Ac can distinguish the two arms (based on prochirality). H 2C CO2 HO C CO2 H C CO2 B H 2O H 2C CO2 HC CO2 C CO2 Ac HO H 2O H H C (Citrate) IC (Iso-citrate) B CO2 HO O2C C Pro S Arm Ac C HO CO2 O2C Pro R Arm Pro S Arm CO2 H H C H C B CO2 Pro R Arm H -- The stereochemistry defined by CS generates only one fit in a specific isomer - where the -O H, CO2 and CO 2 way in three docking locations on Ac . -- The -OH, CO2 three sites. and CO2 make contact with Ac at A Anapleurotic Pathways -- We know three Pathways -- look at Interactions -- Definition: anapleurotic - Today we'll add more detail to this network "filling up" - Start with problem of how different life forms avoid running out of cytoplasmic NAD -- Pathways that maintain catalytic amounts of TCA cycle intermediates Ala Cytoplasm CO2 PLP Glycolysis P G Mitochondrion P CO2 AcCoA PC NAD NADH Important NAD cannot enter mitochondrion NAD / NADH Asp Lipids (later) PDH C IC OA M αKG F NAD / NADH S Glu SCoA Other stuff 1 11