Catabolism
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Microbial metablism Catabolism, anabolism Fermentation Respiration Nitrogen fixtation The synthesis of peptiglydogen An overview of metabolism • Metabolism may be divided into two major parts: catabolism and anabolism. • Catabolism: larger and more complex molecules are broken down into smaller, simpler molecules with the release of energy. • Anabolism: the synthesis of complex molecules from simpler ones with the input of energy. The three stages of catabolism • Much of the ATP derived from the TCA cycle comes from the oxidation of NADH and FADH2 by the electron transport chain. • Carbohydrates and other nutrients serve two functions in the metabolism of heterotrophic microorganisms: 1. They are oxidized to release energy 2. They supply carbon or building blocks for the synthesis of new cell constituents. • Amphibolic pathways: function both catabolically and anabolically SUGAR CATABOLISM • Glycolysis (Embden, Meyerhof Parnas Pathway) – most bacteria – also animals and plants Other pathways for catabolizing sugars • Pentose phosphate pathway (hexose monophosphate shunt) – generates NADPH – common in plants and animals • Entner Doudoroff Pathway – a few bacterial species Glycolysis NAD NADH Glucose Pyruvate C6 C3 ADP ATP Fermentation The energy substrate is oxidized and degraded without the participation of an exogenous or extrenally derived electron acceptor. Usually an intermediate such as pyruvate acts the electron acceptor. Anaerobic conditions Two unifying themes should be kept in mind when microbial fermentation are examined: 1. NADH 2. Pyruvate NAD Short chain alcohols, fatty acids (C3) (C2-C4) Three type fermentation of Saccharomyces cerevisiae I: pyruvateacetaldehydeethanol II: pH7: glycerol III: NaHSO3 Lactic acid fermentation • The reduction of pyruvate to lactate • Homofermentative（同型发酵的） group: produces only lactic acid as sole product • Heterofermentative（异型发酵的） group: produces ethanol, CO2 and lactic acid Respiration Energy-yielding metablism can make use of exogenous or externally derived electron acceptors. Two different type: aerobic respiration: the final electron acceptor is oxygen anaerobic respiration: most often is inorganic such as NO3-, SO42-, CO2 , Fe3+, SeO42 -,) Anaerobic Respiration = Glycolysis + Fermentation NAD NADH ATP NADH NAD Krebs Cycle (C4-C6 intermediate compounds) NAD Pyruvate NADH 3CO2 (C3) (C1) Oxidative phosphorylation NADH NAD O2 H2O ADP ATP Aerobic Respiration = Glycolysis + Krebs Cycle/oxidative phosphorylation • Pyruvate to CO2 – NAD to NADH – glycolysis – Krebs cycle • Oxidative phosphorylation – NADH to NAD – ADP to ATP Oxidative phosphorylation • converts O2 to H20 (oxidative) • converts ADP to ATP (phosphorylation) • electron transport chain • ubiquinones/cytochrome intermediates Sugar as sole carbon source Krebs Cycle C6 Pyruvate (C3) -CO2 Acetate (C2) + CO2 Pyruvate (C3) C4 FATTY ACIDS AS SOLE CARBON SOURCE Krebs Cycle C6 Fatty acids Acetate (C2) C4 C4 + C2 The glyoxylate cycle C3 C6 C6 C2 + C5 C4 C2 C2 C4 C4 C4 Krebs Cycle – biosynthetic – energy producing • Removal of intermediates – must be replenished. • Unique enzymatic replenishment pathway – sugars – fatty acids Nitrogen fixation The reduction of atmospheric gaseous nitrogen to ammonia is callled nitrogen fixation. Nitrogen fixation occurs in: 1. Free-living bacteria.(Azotobacter) 2. Bacteria living in symbiotic association with plants such as legumes(Rhizobium) 3. cyanobacteria Nitrogenase Consistiong of two major protein components: a MoFe protein joined with one or two Fe proteins. 1. The MoFe protein contains 2 atoms of molybdenum and 28 to 32 atoms of iron; 2. The Fe protein has 4 iron atoms Mechnisms of anti-oxygen Nitrogenase is quite sensitive to O2 and must be protected from O2 inactivation within the cell. 1.Respiration protection 2.Hetercyst formation 3.Membrane Nitrogen reduction N2+8H++8e-+16ATP2NH3+H2+16ADP+16Pi Root Nodule Bacteria and Symbiosis with legumes Soybean root nodules Unnodulated soybean Nodulated soybean Steps in the formation of root nodule in a legume infected by Rhizobium Peptidoglycan synthesis Staphylococcus aureus Two carriers participate: uridine diphosphate (UDP) and bactoprenol Bactoprenol is a 55-carbon alcohol that attaches to NAM by a pyrophosphate group and moves peptidoglycan components through the hydrophobic membrane Eight stages of Peptidoglycan synthesis 1. The formation of UDP-NAM and UDP-NAG 2. Amino acids are sequentially added to UDPNAM to form the pentapeptide chain. 3. The NAM-pentapeptide is transferred from UDP to a bactoprenol phosphate at the membrane surfacre. 4. UDP-NAG adds NAG to the NAMpentapeptide to form the peptidoglycan repeat unit. Eight stages of Peptidoglycan synthesis 5. Repeat unit is transported across the membrane to its outer surface by the bactoprenol pyrophosphate carrier. 6. The peptidoglycan unit is attached to the growing end of a peptidoglycan chain to lengthen it by one repeat unit. 7. The bactoprenol carrier returns to the inside of the membrane. A phosphate is released. 8. Peptide cross-links between the peptidoglycan chains are formed by transpeptidation. Peptidoglycan synthesis Cytoplasm Cell Membrane undecaprenol sugar amino acid Cell wall Peptidoglycan Synthesis Transport of peptidoglycan precursors across the cytoplasmic membrane to the growing point of the cell wall The transpeptidation reaction that lead to the final cross-linking of two peptidoglycan chains Penicillin inhibits this reaction Questions • • • • • • What are catabolism and anabolism? What are Fermentation and Respiration? Lactic acid fermentation aerobic respiration, anaerobic respiration Nitrogen fixation Why is Root nodule bacteria and symbiosis so important for legumes? • Eight stages of Peptidoglycan synthesis
