PHM142 Energy Production + The Mitochondria

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Candice Long
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1 PHM142 Energy Production + The Mitochondria 1

2 The Endosymbiont Theory of Mitochondiral Evolution 1970: Lynn Margulis Origin of Eukaryotic Cells Endosymbiant Theory: the mitochondria evolved from free-living bacteria via symbiosis within an anaerobic, nucleus-containing eukaryotic cell mitochondria contain DNA mitochondria contain a distinct protein translation system 2

3 Mitochondrial DNA + Protein Translation ~16-kb, 37 protein-coding genes, high mutation rate Maternal inheritance Encodes 13 proteins necessary for oxidative phosphorylation: mitochondrial ETC, ATP synthase, rrna, trna Similarities between mitochondria + bacteria: transporters, ribosomes, circular RNA and DNA Mitochondrial translation inhibited by Tetracyclines, Chloramphenicol Bone marrow > decline in RBC and WBC production Intestinal epithelial cells > inhibition of replication 3

4 Mitochondrial Energy Production Primary role: energy production (ATP production) Kreb s Cycle (aka Tricarboxylic Acid or Citric Acid Cycle) Electron Transport Chain Oxidative Phosphorylation 4

5 Mitochondrial Structure + Organization Matrix Inner Membrane Outer Membrane Intermembrane Space 5

6 The Kreb s Cycle Glucose (glycolysis) β oxidation of Fatty Acids Amino Acids 6

7 Acetyl-CoA Formation 1. Glucose (glycolysis) 3C pyruvate undergoes oxidation and decarboxylation to form 2C Acetyl-CoA; catalyzed by pyruvate dehydrogenase (5-enzyme complex) CO 2 is lost; NADH is formed 2. Fatty Acids (β oxidation) Activation: thioester bond formation between fatty acids and CoA-SH in the cytosol produces FA-CoA -> transported to the intermembrane space via carnitine -> FA-CoA in the mitochondrial matrix undergoes β oxidation (2C removed/round) 3. Amino Acids deamination forms ketone bodies -> acetyl CoA Glucose (Glycolysis) Fatty Acids (β Oxidation) Amino Acids 7

8 The Steps of the Kreb s Cycle Step 1: Citrate formation (citrate synthase) Acetyl CoA + Oxaloacetate -> Citrate + CoA-SH Step 2. Citrate isomerization to Isocitrate Step 3. α-ketogluterate + CO2 formation (Isocitrate dehydrogenase) Isocitrate is oxidized, NAD+ is reduced to NADH RATE LIMITING Step 4. Succinyl-CoA + CO2 formation (α-ketogluterate dehydrogenase) α-ketogluterate + CoA -> Succinyl-CoA + CO2 NAD+ is reduced to NADH 8

9 The Steps of the Kreb s Cycle Step 5. Succinate formation (Succinyl-CoA synthetase) Succinyl CoA -> Succinate + CoA-SH GDP + Pi -> GTP; then GTP + ADP -> GDP + ATP Step 6. Fumurate formation (Succinate dehydrogenase flavoprotein) Succinate is oxidized, FAD is reduced to FADH2 occurs on the inner mitochondrial membrane Step 7. Malate formation (Fumurase) Step 8.Oxaloacetate regeneration (Malate dehydrogenase) Malate is oxidized, NAD+ is reduced to NADH Acetyl CoA + Oxaloacetate -> Citrate + CoA-SH (Step 1) 9

10 The Kreb s Cycle: Net Results + ATP Yield Pyruvate Dehydrogenase Complex: Pyruvate + CoA-SH + NAD + > acetyl-coa + NADH + CO2 + H + Kreb s Cycle: Acetyl-CoA + 3 NAD + FAD + GDP + Pi + 2 H2O > 2 CO2 + CoA-SH + 3 NADH + 3 H + + FADH2 + GTP 1 NADH = 2.5 ATP 1 FADH2 = 1.5 ATP 1 GTP = 1 ATP 10

11 Kreb s Cycle Regulation 1. Pyruvate dehydrogenase complex Inactivation: increase in ATP/drop in ADP > phosphorylation by PDH kinase Inhibition: ATP and NADH Activation: increase in ADP/decrease in ATP > de-phosphorylation by PDH phosphatase 2. Citrate synthase Inhibition: ATP, NADH, citrate, succinyl-coa 3. Isocitrate dehydrogenase Inhibition: ATP, NADH Activation: ADP, NAD+ 4. α-ketogluterate dehydrogenase Inhibition: ATP, NADH, succinyl-coa Activation: ADP 11

12 The Electron Transport Chain Electrons from NADH/FADH 2 are transferred to carrier proteins along the inner mitochondrial membrane A chain of large multi-subunit protein complexes (I-V) Coupled to proton translocation from the matrix to the intermembrane space > drives ATP synthesis Redox potentials determine direction of electron flow Sazanov, L. Nat Rev Mol Cell Bio

13 Complex I: The ETC: Steps Electrons passed from NADH to FMN coenzyme of Flavoprotein subunit to Coenzyme Q 4 protons pumped to the intermembrane space Complex II: Electrons passed from Succinate to covalently-bound FAD > FADH 2 to Coenzyme Q 0 protons pumped to the intermembrane space 13

14 The ETC: Steps Complex III: Electrons passed from CoQ to 2 cytochrome C (heme: Fe +2 > Fe +3 ) 4 protons pumped to the intermembrane space Complex IV: Electrons passed from cyt C to oxygen > water 2 protons pumped to the intermembrane space 14

15 Oxidative Phosphorylation The Proton-Motive Force: An electrochemical gradient produced by proton pumping -> ph decrease in intermembrane space, voltage difference established Complex V: ATP Synthase Protons flow through F0 portion from the intermembrane space into the matrix the energy of this electrochemical gradient is harnessed by the F1 portion to phosphorylate ADP to ATP The reduction of oxygen + the synthesis of ATP = oxidative phosphorylation 15

16 Mitochondrial Toxicity Bioenergetic poisons: interfere with electrochemical proton gradient generation OR cause its dissipation Mitochondrial poisoning with inhibitors of ETC components causes: muscle weakness, fatigue, fever, hypotension, headache, nausea, acidosis 16

17 ETC Inhibitors Complex I Most vulnerable >60 inhibitors known (e.g. pesticides and rodenticides; neuroleptics, antihistamines, antianginal drugs, antiseptic drugs) Rotenone (plant-derived pesiticide) Amytal (barbiturate) Complex II Antimycin Complex IV Valproate (anticonvulsive drug; liver toxicity) Carbon Monoxide, Cyanide, Azides 17

18 Uncouplers Uncouple the rate of electron transport in the ETC and ATP production Increase oxygen consumption WITHOUT increasing ATP production Prevent ATP synthesis WITHOUT affecting the ETC > decreased efficiency of the ETC/oxidative phosphorylation pathway Decreased ATP/Increased ADP > enhanced oxygen consumption + NADH oxidation > energy from electron transport dissipates > released as heat > fever Examples NSAIDs (salicylates) antipsychotics/antidepressants, antitumor drugs, lipid lowering drugs 18

19 MIDTERM 45 mixed-form questions; 170 points The number of points each question is worth will be indicated Approx. even allocation of points to each instructor-led lecture 9 questions from student presentations (2pts/q) 6 multiple choice questions (2-3 pts/q) ~5 long form questions, depending on succinctness The majority are short answer questions, expected to take no more than a few sentences to answer however, again, this depends on succinctness Write in PEN if you think there is even the slightest chance you will want a regrade

20 PHM142 Maya Latif - maya.latif@mail.utoronto.ca TAs: Ersa Gjelaj - ersa.gjelaj@mail.utoronto.ca Andrew Fleet - andrew.fleet@mail.utoronto.ca Office hour: Thurs 12-1 MIDTERM: Friday October 19th, 11:45-2:45, EX100

CELL BIOLOGY - CLUTCH CH AEROBIC RESPIRATION.

CELL BIOLOGY - CLUTCH CH AEROBIC RESPIRATION. !! www.clutchprep.com CONCEPT: OVERVIEW OF AEROBIC RESPIRATION Cellular respiration is a series of reactions involving electron transfers to breakdown molecules for (ATP) 1. Glycolytic pathway: Glycolysis