Aerobic Metabolism: TCA Cycle - Slides - PDF

Kreb’s / TCA Cycle 1  Fig. 2.8. Kenney et al. 2012. Physiology of Sport… Hum. Kin. Aerobic Stage 1 Metabolism of Glucose Aerobic Stage 2 (slow glyc.)...

Kreb’s / TCA Cycle 1  Fig. 2.8. Kenney et al. 2012. Physiology of Sport… Hum. Kin. Aerobic Stage 1 Metabolism of Glucose Aerobic Stage 2 (slow glyc.) Stage 4  Stage 1 in the Stage 3 sarcoplasm  Stages 2,3,4 in mitochondria Aerobic (“Slow” Glycolysis) 3 Glycolysisin the sarcoplasm yields 2 pyruvate In the mitochondria: Kreb’s Cycle - Stage 3 ◦Primary purpose: to generate electron carriers (NADH & FADH2) Electron Transport Chain (ETC) - Stage 4 ◦Over 90% of ATP synthesis takes place in the respiratory chain of the ETC Stage 2 Stage 4 Stage 3  Electron Carrier Molecules 4 Transport hydrogens and associated electrons To convert pyruvate to lactate (anaerobic) To ETC in mitochondria for ATP generation (aerobic) Nicotinamide adenine dinucleotide (NAD) NAD+ + 2H NADH + H+ Flavin adenine dinucleotide (FAD) FAD + 2H FADH2 Oxidation of these molecules back to NAD+ & FAD drives ATP synthesis in the ETC. Fig. 6.6. McArdle et al. 2015. Exercise Physiology… LWW  Role of Micronutrients 5  Many vitamins serve as coenzymes that are essential to macronutrient metabolism  Niacin (B3) Nicotinamide adenine dinucleotide (NAD)  Riboflavin (B2) Flavin adenine dinucleotide (FAD)  Thiamine (B1) Thiamine pyrophosphate (TPP)  Pantothenic Acid (B5) Precursor for coenzyme A  PDH Rxn 6 Stage 2: Pyruvate dehydrogenase rxn Pyruvate Crosses inner mitochondrial TPP membrane +H+ B vitamins for coenzymes: B1,B3,B5 Irreversible rxn 1 carbon lost as CO2 (Acetyl has 2Cs) Fig. 6.15. McArdle et al. 2015. Exercise Physiology… LWW  TCA Cycle 7  Stage 3: Citric Acid Cycle TCA Cycle Kreb’s Cycle 1) Citrate synthase joins AcCoA with OXA (4C) to form citrate (6 Cs) 3) Isocitrate dehydrogenase  Rate-limiting enzyme for TCA  NADH generated & CO2 lost  TPP is a cofactor for the PDH and α-kg dehydrogenase rxns.  Overall, 1 GTP, 3 NADH, and 1 FADH2 are generated from each TURN of the TCA cycle  Main purpose is to generate electron carriers! Fig. 2.9. Kenney et al. 2015. Physiology of Sport… Hum. Kin. Fig. 6.15. McArdle et al. 2015. Exercise Physiology… LWW Mitochondrial enzymes 8  PDH reaction oxidizes pyruvate and allows it to enter the mitochondria for further oxidation Pyruvate Dehydrogenase (PDH)  Mitochondrial enzymes 9  Citrate synthase reaction combines Acetyl CoA with oxaloacetate (OXA)  Itis the first step of the TCA Cycle and is where AcCoA enters the TCA Citrate Synthase (CS) *You do NOT need to know these structures  Mitochondrial enzymes 10  IDH is the rate-limiting enzyme of the TCA Cycle  Itis also the first of 4 redox reactions (that generate electron carriers) in the TCA Cycle.  You also lose a CO2 in this reaction as you did with PDH + H Isocitrate Dehydrogenase (IDH) (α-kg) *You do NOT need to know these structures Review Questions 11 What are two of the purposes of the ETC in metabolism? What is the main purpose of the TCA Cycle? Know the PDH reaction in detail and label all of the parts of this redox reaction. Example: What is oxidized by the PDH reaction? Know what is happening in the citrate synthase and the IDH reaction. What is the rate-limiting enzyme of the TCA Cycle? Figure & Notes References 12  Kenney, Wilmore, & Costill. Physiology of Sport & Exercise, 5th Edition. Human Kinetics, 2015.  McCardle, Katch, Katch. Exercise Physiology: Nutrition, Energy, and Human Performance, 8th Edition. Wolters Kluwer Health, 2015.