General Biochem 5 - ETC PDF

Energy – Electron Transport Chain Dr. I. Fraser Dr. Hurnik BMS 100 Outline Lecture Review of ETC Components ATP Synthase Adenine Nucleotide Translocase Outline the catabolic pathways that produce reduced coenzymes (NADH, FADH2) Glycolysis Shuttle systems ATP generated when glucose is converted to CO...

Energy – Electron Transport Chain Dr. I. Fraser Dr. Hurnik BMS 100 Outline Lecture Review of ETC Components ATP Synthase Adenine Nucleotide Translocase Outline the catabolic pathways that produce reduced coenzymes (NADH, FADH2) Glycolysis Shuttle systems ATP generated when glucose is converted to CO2 and H2O Beta oxidation Citric acid cycle Non-shivering thermogenesis ETC review Let’s review the basics of the electron transport chain from pre-learning: Found in the _______ mitochondrial membrane Takes electrons from NADH and FADH2 Passes them down a chain of electron carriers with increasing electron affinity Eventually donates them to _______ to make water Energy from electron movement used to pump H+ into the intermembrane space Creates an H+ gradient that is used to drive the production of ATP ETC Outer mitochondrial membrane III I FADH2 FAD+ II Succinate DHG II NADH NAD+ IV ATP synthase H+ gradient is used to drive the production of ATP A closer look at ATP synthase ATP synthase continued ATP generated § Each NADH generates ~3 ATP § Each FADH2 generates ~2 ATP Why do you suppose FADH2 generates less ATP? ATP synthesis How does the ATP generated by ATP synthase get to the cytosol? § Adenine nucleotide translocate antiporter exchanges ATP for ADP § Note – we also need a phosphate translocate symporter which brings the phosphate group into the mitochondrial matrix Inner mitochondrial membrane Answer in pairs – 5 minutes Let’s consider how the various catabolic pathways feed into the electron transport chain to generate ATP. § Which three catabolic pathways produce indirect energy intermediates that feed into the ETC? Catabolic pathway 1. 2. 3. Cellular location 1 - Glycolysis During glycolysis, two NADH are produced § In the cases of red blood cells (no mitochondria) or anaerobic conditions, why does this NADH not enter the ETC? Review: what happens to it instead? Aside – Reminder: anaerobic conditions In the cases of red blood cells (no mitochondria) or anaerobic conditions: Pyruvate is converted to lactate Enzyme: Lactate dehydrogenase NAD+ is regenerated for what purpose? This is called the _____ cycle Lactate travels via the blood to the liver, where it is converted back to pyruvate (enzyme?) and used for what purpose? At home review slide – Cori Cycle Liver Muscle Glucose Glucose Glycolysis Gluconeogenesis 2 NADH 2 NAD+ 6 ATP Blood 2 ATP 2 pyruvate 2 NADH Glucose 2 pyruvate LDH 2 lactate 2 NAD+ LDH 2 lactate 2 lactate 1 - Glycolysis Under aerobic conditions: § This NADH must cross into the matrix of the mitochondria to enter the ETC, § but the inner mitochondria membrane is impermeable to NADH 1 – Glycolysis – Shuttle systems There are two shuttle systems in place to allow NADH from the cytosol to contribute to ETC energy production in the mitochondria § 1. Malate Aspartate shuttle Moves NADH into the matrix to enter the ETC § 2. Glycerol-phosphate shuttle Converts NADH to FADH2, which then enters the ETC from the intermembrane space 1 – Glycolysis – Shuttle systems 1. Malate Aspartate shuttle: 1 – Glycolysis – Shuttle systems 1. Malate Aspartate shuttle: 1. NADH from glycolysis is used to convert OAC to malate 2. Malate can cross the I.M.M. via an antiporter 3. Malate converts back to OAC, while NADH is regenerated and can now enter the ETC at complex _____ 1 – Glycolysis – Shuttle systems 1. Malate Aspartate shuttle: 4. OAC converts to Asp 6. Asp converts back to OAC: ready to start again! 5. Aspartate can cross the I.M.M. via an anti-porter 1 – Glycolysis – Shuttle systems Preview - A closer look at steps 4 & 6 (FYI for now) Transamination reactions More to come in the amino acid metabolism lecture in week 15 1 – Glycolysis – Shuttle systems 2. Glycerol Phosphate shuttle 1 – Glycolysis – Shuttle systems 2. Glycerol Phosphate shuttle 1. NADH is produced in glycolysis 3. Glycerol 3P can enter the intermembrane space 4. Glycerol 3-P is converted back to DHAP by mitochondrial glycerol-3-P DH (embedded in the I.M.M.), generating FADH2 2. DHAP is reduced to glycerol 3phosphate, regenerating NAD+ for glycolysis 5. FADH2 does not cross I.M.M but directly enters the ETC via mitochondrial G3P DH Glucose Pyruvate NAD+ ETC NADH Glycerol-3-P Outer mitochondrial membrane DHAP DHAP Glycerol-3-P FAD+ FADH2 m Glycerol 3P DHG I III FADH2 FAD+ II Succinate ubiquinone DHG II NADH NAD+ NADH using the glycerol phosphate shuttle, generates 1 less ATP – why? IV Complete Oxidation of Glucose Pathway Enzyme Glycolysis Hexokinase -1 Phosphofructokinase-1 -1 Glyceraldehyde 3-P Dehydrogenase ETC: 2 NADH 4 or 6 Phosphoglycerate Kinase Substrate level 2 Pyruvate Kinase Substrate level 2 Connector Pyruvate Dehydrogenase ETC: 2 NADH 6 CAC Cycle Isocitrate Dehydrogenase ETC: 2 NADH 6 a-ketoglutarate Dehydrogenase ETC: 2 NADH 6 Succinate Thiokinase Substrate level 2 Succinate Dehydrogenase ETC: 2 FADH2 4 Malate Dehydrogenase ETC: 2 NADH 6 Cytosol Mitochondria Energy Production ATP Total 36 or 38 2 – Beta oxidation Since beta-oxidation occurs in the mitochondrial matrix, no shuttle systems are required Within each round of beta oxidation, the following are produced: § ___ FADH2 § ___ NADH § 1 acetyl CoA (2 acetyl CoA in last round) Dehydrogenase Dehydrogenase β 2 – Beta oxidation – each round FADH2 Enters the ETC at its own complex, similar to complex II (see next slide) Dehydrogenase NADH enters the ETC at complex _______ Dehydrogenase Acetyl-CoA enters the CAC β 2-Beta oxidation – more details Outer mitochondrial membrane ETF dehydrogenase FADH2 from Beta-oxidation enters via a dehydrogenase enzyme complex (FYI ETF dehydrogenase/ Q oxidoreductase) 3 - CAC Since the CAC also occurs in the mitochondrial matrix, there are no shuttles required. Within each cycle of the CAC, there are: § _______ NADH produced § _______ FADH2 produced FADH2 enters the ETC at complex _______ NADH enters the ETC at complex _______ Thinking Question How many ATP are generated when acetyl CoA from beta ox is oxidized to CO2 and H2O within the CAC How many ATP are generated when acetyl CoA from glycolytic pyruvate is oxidized to CO2 and H2O within the CAC Putting it all together… Cytosol IM Space (B) enters the ETC here, after being generated from glycolytic NADH via the ____ shuttle. Complex I Cyt. C G-3-P DH Complex III Complex IV CoQ Complex II (succinate DH) (C) from ? enters here ETF DH (D) from ? enters here (A) from ?, ?, and ? enters here. Of these cycles, (A) from ? requires a transport system called the _________ shuttle. Matrix Summary Electrons are passed from one complex to another until they are finally passed to O2 to make H2O Since the electron carriers are in order of increasing electron affinity, energy is released with each pass of the electrons This energy is used to pump H+ from the mitochondrial matrix to the intermembrane space The resulting “chemiosmotic” or “electrochemical” gradient is then harnessed to generate ATP as H+ re-enters the mitochondrial matrix through the ATP synthase Thinking Question If an individual is anoxic how does this affect ATP synthesis If a cell has adequate ATP how does this affect ATP synthesis, ETC, and the Citric Acid Cycle? Non-Shivering Thermogenesis Newborn babies, hibernating animals and coldadapted animals need to generate more heat than is produced by normal metabolism § Have lots of brown fat Brown due to large # of mitochondria Contains thermogenin, a protein that uncouples the ETC by translocating H+ back to the matrix § In other words, H+ in the intermembrane space move back into the matrix through thermogenin instead of through ATPase Heat is produced rather than ATP ETC Outer Membrane Cytosol InterMembrane Space Inner Membrane Q II c H+ e- FADH2 III H+ Matrix H+ e- H+ e- I H+ NADH e- H+ H+ H+ IV 4 e- + 4H+ + O2 2H2O ATP Synthase H+ ATP I, II, III, IV, Q and c = parts of the ETC that accept/donate e Resulting in pumping of e- into intermembrane space H+ move back out via ATP Synthase, which makes ATP