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1. 2. 3. 4. 5. 4. 5. Energy Transformation: Cellular Respiration Outline Sources of cellular ATP Turning chemical energy of covalent bonds between C-C into energy for cellular work (ATP) Importance of electrons and H atoms in oxidation-reduction reactions in biological systems Cellular mechanisms of ATP generation The four major central metabolic pathways Glycolysis- Fermentation Transition step Krebs Cycle Electron Transport chain and oxidative phosphorylation Poisons of cellular respiration and their mechanisms of action. Use of biomolecules other than glucose as carbon skeletons & energy sources A cell has enough ATP to last for about three seconds http://health.howstuffworks.com/sports-physiology3.htm Necessary ATP is supplied to muscle cells by 1. Phosphagen system (8 to 10 seconds.) 2. Glycogen-lactic acid system (90 seconds)- glucose 3. Aerobic Respiration (unlimited)- glucose Phosphagen system (muscle fibers) * • Creatine phosphate contains (a high-energy phosphate compound). • Creatine kinase transfers the phosphate to ADP to form ATP. Creatine-Phosphate (tri) Creatine Kinase Creatine-Phosphate + ADP (Tri) Creatine-Phosphate + ATP (*) Arezki Azzi et al. Protein Sci 2004; 13: 575-585 (Di) During cellular respiration the potential energy in the chemical bonds holding C atoms in organic molecules in turned into ATP. In presence of oxygen complete breakdown ATP C-C-C-C-C-C + O2……………… CO2 + H2O + large amount In absence of oxygen incomplete breakdown C-C-C-C-C-C ……………… 2 C-C-C + ATP small amount Cellular respiration: ATP is produced aerobically, in the presence of oxygen Fermentation: ATP is produced anaerobically, in the absence of oxygen Chemical bonds of organic molecules Chemical bonds involve electrons of atoms Electrons have energy Chemical bonds are forms of potential energy If a molecule loses an electron does it lose energy? When a chemical bond is broken sometimes electrons can be released Oxidation-Reduction • Oxidation: removal of electrons. • Reduction: gain of electrons. • Redox reaction: oxidation reaction paired with a reduction reaction. Electron Carriers in Biological Systems The electrons associated with hydrogen atoms. Biological oxidations are often dehydrogenations Soluble electron carriers NAD+, and FAD (ATP generation) NADP+ (biosynthetic reactions) Nicotinamide Adenine Dinucleotide (NAD+) a co-enzyme that acts as an electron shuttle (Niacin) 2 e– + 2 H+ NAD+ 2 e– + H+ NADH H+ Dehydrogenase + 2[H] (from food) Nicotinamide (oxidized form) + H+ Nicotinamide (reduced form) Flavin Adenine Dinucleotide (FAD+) is another co-enzyme that acts as an electron shuttle (Vitamin B2) In Metabolic pathways Oxidation Reduction • Energy loss or gain • Exergonic or endergonic • Catabolic or anabolic In cells, energy is harvested from an energy source (organic molecule) by a series of coupled oxidation/reduction reactions (redox) known as the central metabolic pathways becomes oxidized becomes reduced Dehydrogenase Metabolic Pathways Linear Pathways Branched Pathways Cyclic Pathways An overview of the central metabolic pathways • • • • Glycolysis Transition step Tricarboxylic acid cycle (TCA or Krebs cycle) The Electron Transport Chain and oxidative phosphorylation Mechanisms of ATP Generation during cellular respiration 1. Oxidative phosphorylation/ Chemiosmosis • • • • ADP and inorganic PO-4 ATP synthase Cellular respiration in mitochondria Electron Transport Chain Generation of ATP 2. Substrate-level phosphorylation -Transfer of a high-energy PO4- from an organic molecule to ADP - Different enzymes - During glycolysis and the TCA or Krebs cycle Glycolysis • Multi – step breakdown of glucose into intermediates • Turns one glucose (6-carbon) into two pyruvate (3-carbon) molecules • Generates a small amount of ATP (substratelevel phosphorylation) • Generates reducing power - NADH + H+ Figure 9.18 Pyruvate as a key juncture in catabolism Fermentation An extension of glycolysis Takes place in the absence of oxygen (anaerobic) Regenerates NAD+ from NADH + H + ATP generated by substrate - level phosphorylation during glycolysis • Does not use the Krebs cycle or ETC (no oxidative phosphorylation) • A diversity of end products produced (i.e. lactic acid, alcohols, etc.) • • • • Figure 9.17a Fermentation Figure 9.17b Fermentation Figure 9.9 A closer look at glycolysis: energy investment phase Figure 9.9 A closer look at glycolysis: energy payoff phase The energy input and output of glycolysis Energy investment phase Glucose Glycolysis Citric acid cycle 2 ATP used 2 ADP + 2 P Oxidative phosphorylation Energy payoff phase ATP ATP ATP 4 ADP + 4 P 2 NAD+ + 4 e– + 4 H+ 4 ATP formed 2 NADH + 2 H+ 2 Pyruvate + 2 H2O Net Glucose 4 ATP formed – 2 ATP used 2 NAD+ + 4 e– + 4 H+ 2 Pyruvate + 2 H2O 2 ATP 2 NADH + 2 H+ Transition step • Under aerobic conditions, the pyruvate produced during glycolysis is directed to the mitochondrion. • A multi-enzyme complex, spanning the 2 mitochondrial membranes, turns pyruvate (3-carbon) into Acetyl-CoA (2-carbon) and releases one CO2 molecule • Uses coenzyme A (Vit B derivative) • Generates reducing power NADH + H+ Figure 9.10 Conversion of pyruvate to acetyl CoA, the junction between glycolysis and the Krebs cycle Krebs or TCA Cycle • • • • • A cyclical pathway Accepts – acetyl – CoA Generates 2 – CO2 molecules (for every acetyl-CoA Generates reducing power NADH + H+ and FADH2 Generates a small amount of ATP (substrate-level phosphorylation) A closer look at the Krebs cycle Figure 9.12 A summary of the transition step and Krebs cycle Figure 9.5 An introduction to electron transport chains Electron Transport Chain and ATP generation Electron transport chain: • membrane-embedded or bound electron carriers • Mostly proteins with nonprotein groups. • NADH vs. FADH2 • No direct formation of ATP • Pumps H+ into the intermembrane space Oxidative Phosphorylation and ATP generation ATP Generation : • Membrane-embedded protein complex , ATP synthase • Proton-motive force • Direct formation of ATP by Chemiosmosis Chemiosmosis: the coupling of the transport of H+ across membrane by facilitated diffusion with chemical reaction producing ATP ATP Synthase Gradient: The Movie http://vcell.ndsu.edu/animations/at pgradient/movie.htm Chemiosmosis couples the electron transport chain to ATP synthesis Certain poisons interrupt critical events in cellular respiration • Block the movement of electrons • Block the flow of H+ through ATP synthase • Allow H+ to leak through the membrane Cyanide, carbon monoxide Rotenone H+ H+ H+ Oligomycin H+ H+ + H H+ H+ H+ ATP Synthase DNP FADH2 NADH NAD+ H+ FAD 1 O2 + 2 H+ 2 H+ H+ Electron Transport Chain H2 O ADP + P ATP Chemiosmosis Energy yield: How many ATP molecules are generated during cellular respiration of a single glucose molecule? Sources of cellular glucose • glucose from food in the intestine • glycogen supplies in the muscles • breakdown of the Liver's glycogen into glucose The Catabolism of various food molecules Beta oxidation http://www.brookscole. com/chemistry_d/templ ates/student_resources /shared_resources/ani mations/carnitine/carni tine1.html Simple lipids • Triglycerides consist of glycerol and fatty acids • Fatty acids broken down into through beta oxidation Proteins Protein Extracellular proteases Deamination, decarboxylation, dehydrogenation Amino acids Organic acid Krebs cycle and glycolysis Transition step Feedback control of cellular respiration Phosphofructokinase Allosteric enzyme Activity modulated by inhibitors and activators Adjustment of cellular respiration in response to demand Food, such as peanuts Carbohydrates Sugars Fats Proteins Glycerol Fatty acids Amino acids Amino groups Pyruvate Glucose G3P GLYCOLYSIS Acetyl CoA ATP CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) Food molecules provide raw materials for biosynthesis consuming ATP ATP needed to drive biosynthesis ATP CITRIC ACID CYCLE GLUCOSE SYNTHESIS Glucose Pyruvate G3P Acetyl CoA Amino groups Amino acids Proteins Fatty acids Glycerol Fats Cells, tissues, organisms Sugars Carbohydrates