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BIO 411 - Medical Microbiology Chapter 4 Bacterial Metabolism and Growth Metabolic Requirements • Bacteria’s first priority – Survive and Reproduce • To do this they need: – Source of Energy (for human pathogens sugars, fats, and proteins) – Raw materials to build all cell structures • • • • Carbon source Nitrogen source Water Ions – Table 4-1 Metabolic Requirements • Different O2 needs: – Obligate anaerobes (Clostridium perfringens, and others) – Obligate aerobes (Mycobacterium tuberculosis) – Facultative anaerobes (most bacteria) Metabolic Requirements • Differences is metabolic requirements: – E. coli – Treponema pallidum Overview of Metabolism • Metabolism = the sum of all chemical processes within a cell • Consists of: – Catabolism - breakdown of nutrients for energy and building blocks (precursor metabolites) – Anabolism - building of cellular components using energy and building blocks • These both occur through metabolic pathways • Overview of bacterial metabolism. (extracellular digestion, etc.) Metabolism of Glucose (cont.) • Bacteria can catabolize glucose by (in order of decreasing efficiency): – Respiration - Final electron acceptor in the electron transport chain is an inorganic molecule • Aerobic - O2 is the final e- acceptor • Anaerobic - something else is (NO3-, SO42- , CO2 ) – Fermentation - final electron acceptor is an organic molecule Respiration • Deals with three metabolic pathways: – Glycolysis (Embden-Meyerhof-Parnas) – TCA cycle (also called the Krebs Cycle and the citric acid cycle) – Electron Transport System Respiration (cont.) • Glycolysis: – 1 glucose molecule is split into 2 molecules of pyruvate – 2 ATP are gained for every glucose molecule – 2 NADH are produced for every glucose molecule • NADH picks up high-electrons lost by glucose – Figure 4-2 Respiration (cont.) • Conversion of pyruvate to acetyl-CoA – pyruvate cannot enter directly into the TCA cycle – 1 NADH is produced for every pyruvate – 1 molecule of CO2 is release for every pyruvate Respiration (cont.) • TCA cycle: – cyclic metabolic pathway – produces 1 ATP for every acetyl-CoA – produces 3 NADH for every acetyl-CoA – produces 1 FADH2 for every acetyl-CoA – All 6 carbons from the original glucose molecule have been converted to CO2 by the end of the TCA cycle – Figure 4-4 Respiration (cont.) • Electron Transport System – All NADH molecules formed in the previous steps bring the electrons they have gained to the electron transport system – These electrons are passed along a series of membrane proteins • eventually the electrons are given to the final eacceptor (O2 to form H2O, etc.) • Figure 4-5 Respiration (cont.) – These proteins use the energy of the electrons to pump protons across the membrane (from the inside of the cell to the outside) – This pumping of protons across the membrane generates an electrochemical gradient across the membrane – These protons are then brought back through the membrane and the associated energy is used to produce ATP – Analogy involving a dam Respiration (cont.) • One molecule of glucose can produce 38 ATP through this complete process – Figure 4-6 Aerobic vs. Anaerobic Respiration • If oxygen is the final electron acceptor, the process is called aerobic respiration • If some other molecule is the final electron acceptor, the process is called anaerobic respiration – sulfate reducers, nitrate reducers, methane bacteria Fermentation • Fermentation begins with glycolysis – Fermentation usually occurs under anaerobic conditions (no oxygen = no final electron acceptor) – Problem: 2 NADH don’t give off e- at the ETS • NADH build-up would eventually shut down glycolysis – Fermentation unloads electrons on pyruvate or a derivative of pyruvate • this regenerates NAD+ so glycolysis can continue – Figures 4-1 and 4-3 Lipid Catabolism • Lipids are broken down to glycerol and fatty acids • Glycerol enters glycolysis • Fatty acids undergo beta-oxidation to form acetyl-CoA • Figure 4-1 Protein Catabolism • Proteins are broken down outside the cells by protease enzymes. • The amino acids are brought inside the cells and funnel into glycolysis or the Krebs cycle • Figure 4-1 Anabolism • What is anabolism? • Anabolism also occurs through metabolic pathways – Many times it’s just the opposite of protein, lipid and carbohydrate catabolism • Figures 4-1 and 4-7 Disease of the Day • • • • Dental Caries (cavities) Etiology – Streptococcus mutans Reservoir – Our Mouthes (normal flora) Transmission and Development – Transmission – NA – Development – Importance of sucrose (Figure 25.3) Disease of the Day • Prevention and Control – Brushing/Flossing – Fluoride – Decrease sucrose intake