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Transcript
METABOLISM BACTERIAL METABOLISM CHAPTER 5 • Metabolism is the sum of the chemical reactions in an organism. • Catabolism is the energy-releasing processes. • Anabolism is the energy-using processes. • Catabolism provides the building blocks and energy for anabolism. What promotes chemical reactions? • The collision theory states that chemical reactions can occur when atoms, ions, and molecules collide. • Activation energy is needed to disrupt electronic configurations. • Reaction rate is the frequency of collisions with enough energy to bring about a reaction. • Reaction rate can be increased by increasing temperature, pressure, and reactant concentration. What promotes chemical reactions in biological systems? Holoenzyme: Apoenzyme + cofactor • Enzymes are biological catalysts that can accelerate reactions without increasing temperature. (Importance?) – Specific for a chemical reaction; not used up in that reaction • Apoenzyme: protein • Cofactor: Nonprotein component – Coenzyme: Organic cofactor • NAD+, NADP+, FAD, Coenzyme A 1 Enzymes change substrate to products The turnover number is generally 1-10,000 molecules per second. Enzymes can be denatured by temperature and pH Factors that influence an enzyme Competitive Inhibition of enzyme 2 Non-competitive inhibition of enzyme Feed-back inhibition of enzyme • Build-up of end product inhibits action of enzyme in previous reaction (usually first reaction of pathway) Classification of enzymes • • • • Oxidoreductase Transferase Hydrolase Lyase • Isomerase • Ligase Oxidation-reduction rxns Transfer functional groups Hydrolysis Removal of atoms without hydrolysis Rearrangement of atoms Joining of molecules, uses ATP • A metabolic pathway is a sequence of enzymatically catalyzed chemical reactions in a cell. • Metabolic pathways are determined by enzymes. • Enzymes are encoded by genes. Oxidation-reduction reactions • Oxidation is the removal of electrons. • Reduction is the gain of electrons. • Redox reaction is an oxidation reaction paired with a reduction reaction. 3 In biological systems, the electrons are often associated with hydrogen atoms. Biological oxidations are often dehydrogenations. Energy from catabolic reactions is stored in high energy, unstable bonds of ATP (adenosine triphosphate) to be used in anabolic reactions. NADH has more energy than NAD: H+ produced = proton motive force Types of phosphorylation to generate ATP • Substrate-level phosphorylation is the transfer of a high-energy PO4- to ADP. Types of phosphorylation to generate ATP • Oxidative: – Energy released from the transfer of electrons (oxidation) of one compound to another (reduction) is used to generate ATP by chemiosmosis (electron transport chain) • Photophosphorylation: – Light causes chlorophyll to give up electrons. Energy released from the transfer of electrons (oxidation) of chlorophyll through a system of carrier molecules is used to generate ATP. Types of Bacterial Metabolism • Fermentation • Respiration – Aerobic Respiration – Anaerobic Respiration • Photosynthesis CARBOHYDRATES • The breakdown of carbohydrates to release energy – Glycolysis – Krebs cycle – Electron transport chain 4 GLYCOLYSIS (EMBDENMEYERHOFF PATHWAY) The oxidation of glucose to pyruvic acid, produces ATP and NADH. • Respiration and Fermentation have the same first step: Glycolysis • Glucose + 2 ATP + 2 ADP + 2 PO4– + 2 NAD+ → 2 pyruvic acid + 4 ATP + 2 NADH + 2H+ • Net gain of 2 ATP; 2 NADH; and 6 precursor metabolites • Does not require O2 Glycolysis ALTERNATIVES TO GLYCOLYSIS • Pentose phosphate pathway (hexose monophosphate shunt: – Operates with glycolysis to breakdown 5-C sugars – Gain of 1 ATP Aerobic Respiration • The COMPLETE breakdown of glucose to CO2 and H2O with O2 serving as the final electron acceptor (TEA=terminal electron acceptor) • Entner-Doudoroff pathway: – Produces NADPH and 1 ATP – Does not involve glycolysis – Pseudomonas, Rhizobium, Agrobacterium 5 Intermediate Step KREBS CYCLE • Oxidation of acetyl CoA produces NADH and FADH2 • AKA Tricarboxylic Acid Cycle (TCA) or Citric Acid Cycle • Potential energy stored in acetyl CoA released in steps to carrier coenzymes primarily NAD+ to NADH • Pyruvic acid (from glycolysis) is oxidized and decarboyxlated Figure 5.13.1 The Electron Transport Chain • A series of carrier molecules that are, in turn, oxidized and reduced as electrons are passed down the chain. • Energy released can be used to produce ATP by chemiosmosis. – Proton motive force: source of energy for • Synthesis of ATP • Active Transport of substances across membrane • Flagella movement A model for the ETC Electron Transport Chain 6 Respiration • Aerobic respiration: The final electron acceptor in the electron transport chain is molecular oxygen (O2): – C6H12O6 + 6 O2 + 38ADP +38 P=6 CO2 + 6 H2O + 38ATP – Anaerobic respiration: The final electron acceptor in the electron transport chain is not O2. Yields less energy than aerobic respiration because only part of the Krebs cycles operations under anaerobic conditions. Anaerobic respiration Electron acceptor Fermentation • Releases energy from oxidation of organic molecules • Does not require oxygen • Does not use the Krebs cycle or ETC • Uses an organic molecule as the final electron acceptor Products NO3– NO2–, N2 + H2O SO4– H2S + H2O CO32 – CH4 + H2O Fermentation Figure 5.14 7 Fermentation products can vary Fermentation • Alcohol fermentation. Produces ethyl alcohol + CO2 • Lactic acid fermentation. Produces lactic acid. – Homolactic fermentation. Produces lactic acid only. – Heterolactic fermentation. Produces lactic acid and other compounds. Fermentation end products Types of fermentation Fermentation ATP Yield Figure 5.23 8 Comparison of three types of metabolism COMPARISON OF METABOLISM • Aerobic respiration: Total ATP Prokaryotes=38 Eukaryotes=34 – Final electron receptor is O2 • Anaerobic respiration: ATP >2<38 – Absence of oxygen – Final electron receptor is inorganic molecule • Fermentation: Yield = 2 ATP – Final electron receptor is organic molecule – Endproducts: Lactic acid/Alcohol Photosynthesis Pathway Eukaryote Prokaryote Glycolysis Cytoplasm Cytoplasm Intermediate step Cytoplasm Cytoplasm Krebs cycle Mitochondrial matrix Mitochondrial inner membrane Cytoplasm ETC • Conversion of light energy to chemical energy • C fixation = conversion of CO2 to sugars • Light dependent stage • Calvin-Benson cycle Plasma membrane 9 Nutritional Pattern Classification Chemotrophs • Use energy from chemicals. • Energy: – Chemoheterotroph – Phototrophs – Chemotrophs Glucose NAD+ • Carbon source: ETC – Autotrophs – Heterotrophs Pyruvic acid • Almost all medically important microorganisms are chemoheterotrophs. NADH ADP + P ATP • Energy is used in anabolism. Phototrophs Chemotrophs • Use energy from chemicals. • Use light energy. – Chemoautotroph, Thiobacillus ferroxidans Chlorophyll 2Fe2+ ETC NAD+ ETC 2Fe3+ NADH Chlorophyll oxidized ADP + P ADP + P ATP ATP 2 H+ – Energy used in Calvin-Benson cycle to fix CO2 • Photoautotrophs use energy in the CalvinBenson cycle to fix CO2. • Photoheterotrophs use energy. 10