S51: Oxidative Phosphorylation, Reactive Oxygen Species, and Aging Learning Objectives 1) Understand how electron carriers, ex. NADH, link oxidation of energy nutrients w/the electron transport chain and oxidative phosphorylation. 2) Describe how energy is derived from oxidation/reduction rxns of the electron transport chain to generate the mitochondrial proton gradient. 3) Understand how the proton motive force is coupled to ATP synthesis and uncoupled for heat generation. 4) Appreciate what ROS are, anti-oxidation systems in our bodies which destroy ROS and their relationship to aging. Catabolism of Major Macromolecules of E: Overview - Acetyl CoA= universal molecule to go into the TCA!- Main idea: to transfer e-'s from the food where they started to universal E carriers!- TCA= where we make most NADH and FADH2! Electron Transport and Oxidative Phosphorylation!- E aassoc. w/redox molecs used to make ATP by passing e-'s down the e- transport chain!- Reoxidation of NADH and FADH2 reduces O2 --> H20!- Couple downhill e- transport to uphill gen. of proton gradient!- E from pH gradient across inner mitochond. membrane drives ADP + Pi --> ATP = oxidative phosphorylation!- During e- transport, reactive oxygen species (ROS) w/reactive unpaired e-'s are gen. as side product --> damage stuff, antioxidant systems remove them!- Electrons from Oxidation of E nutrients carried on Electron Carriers!- NAD + hydride ion (H-) <--> NADH (made from Niacin)!- FAD + 2H's <--> FADH2!- Organization of Mitochondria: ATP Generating Organelle - Outer mitochondrial membrane: permeable to MW < 10,000, lipid metab. enzymes!- Inner mitochondrial space: has enzymes for interconverting adenine nucleotides!- Inner mitochondrial membrane: impermeable to most incl. protons, has: ETC (electron transport chain), ATP synthase!- Matrix: has TCA and DNA!- Electron Transport Complexes!- ETC consists of 4 protein complexes in the inner mitochondrial membrane, each has electron carriers w/diff. E (bind e's w/increasing affinity)!- accept e-s from NADH (complex I) or FADH2 (complex II) to become reduced and pass them along!- E released use to pump H+ (protons) across IMM --> proton gradient!- Complex IV donates e-s to O2 --> H20 !- FADH2 is part of Complex II!- Complex I: NADH Q reductase!- Complex II: Succinate-Q reductase!- Complex III: cytochrome reductase!- Complex IV: cytochrome oxidase!- As these e-s are being transferred, we're gaining E! Use this E to pump protons out of the matrix...ultimately, e-s transferred to molecular oxygen to make water!- e- transfers: oxidation reduction rxns: reduced A + oxidized B --> oxidized A + reduced B!- ease it gives up e-= oxidation reduction potential, volts!- if you go from more NEG reduction potentials to more POS reduction potentials --> release E, we use to move protons!- NADH: Pumps 10 protons on, FADH2: Pumps 6 protons out!- Proton Motive Force Drives ATP Synthesis!- Using the H+ gradient (and the charge diff.) to drive the molecular machine= ATP synthase!- Matrix: low H+, more NEG, Inner mitochon. space: high H+, more POS!--> electrochemical gradient!- ATP synthase= large complex of sev. diff. proteins in the IMM allows H+ to pass back into matrix and uses this E + ADP + Pi --> ATP!- As protons come into Fo, they spin around the c subunits --> cause an electrical charge --> spins the y subunit --> changes the conformation of each of the heterodimers (alpha and beta) --> brings ADP and Pi together --> makes ATP --> has low affinity for ATP --> releases ATP!- ATP synthase could run the other way too if [ ]s change!- Inhibitors of oxidative phosphorylation are potent poisons - Rotenone (Complex I), antimycin (C III), azide cyanide CO (C IV), oligomycin (ATP synthase)!- ATP yield from oxidative phosphorylation - Ideally: 1 NADH --> 3 ATP, really: 1NADH --> 2.5 ATP!- Ideally: 1 FADH2 --> 2 ATP, really: 1FAHD2 --> 1.5 ATP!- Adenine Nucleotide Translocase!- Need to get ADP IN (to be made into ATP) and ATP OUT (to be used by cell), use translocase!- Driven by pH gradient, favors moving - ATP out!- 2nd transporter in IMM for Pi + H+ into matrix!- Uncoupling and Heat Generation!- Brown adipose tissue has Uncoupling Protein (UCP) in inner mitochondrial membrane--> dissipates proton gradient w/o making ATP (--> makes oxidative phoshphory ineff.), lets H+ thru!- E released as heat !- Infants!- Reactive Oxygen Species - A little of metabolized O2 forms superoxide anion radical: O2-, is very reactive, but shortlived!- breaks down to H202 + hydroxyl radicals = ROS!- ROS can mod proteins, DNA, lipids, interfere w/normal function --> lead to aging?!- we have cellular defense mechs for dealing w/ROS: superoxide dismutase, catalase, glutathione peroxidase!- Glutathione (GSH) acts as an antioxidant in cells !- Oxidative Stress and Aging!- theory: ROS and oxidative stress lead to damage to cellular molecules!- decline in function of ETC --> make more ROS, free-radical finding enzymes!--> damage adds up --> leads to functional decline and cell death!!S51: The Citric Acid Cycle Learning Objectives 1) Understand how the oxidation of acetyl CoA to CO2 is completed in the TCA 2) Appreciate how electrons are derived from acetate oxidation are used to generate reduced electron carriers for fueling the electron transport chain and oxidative phosphorylation 3) Analyze the amt of energy that can be obtained from each turn of the TCA 4) Recognize that the TCA cycle is also used for biosynthetic purposes in the cell and how intermediates of the TCA cycle are resupplied Citric Acid Cycle: Overview!- 8 rxns, acetate (from acetyl CoA) oxidized to 2 molecules of CO2 - 8 e-'s from acetate used to reduce 3 NAD+ to NADH and 1 FAH to FADH2!- donate their e-s to the ETC!- 1 GTP generated from substrate-level phosphorylation!- 10 ATP equivalents generated for each turn of the cycle !- Rxns occur in mitochondrial matrix - Other names: Citric acid cycle, trixcarboxylic acid cycle (TCA), Krebs cycle!- Coenzyme A= substrate the starts the rxn= the activated carrier of acyl groups in metabolis, portion of it we can't make= vitamin B5 !- has high E sulfur bond --> breaking it drives the 1st rxn to citrate!- just a part of acetyl Co-A!- Acetyl Co-A= the entry point for catabolism of carbs, fats, and aa's into the TCA!- has high E thioester bond, has 4 e- pairs that are used to reduce (3) NAD+ and (1) FAD!- Steps 1 and 2!1) acetyl group of acetyl CoA condenses w/oxaloacatate to form citrate (driven by E of
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