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Chapter 5

Chapter 5. Microbial metabolism. I. Catabolic and anabolic reactions. Metabolism : 生物體中所有化學反應之總和 . Catabolism : degradation ( 放能 ) Anabolism : synthesis ( 吸能 ) 能量反應 : ATP. Fig. 5.1. II. Enzymes. Enzymes : biocatalyst Activation energy Substrate, product.

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Chapter 5

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  1. Chapter 5 Microbial metabolism

  2. I. Catabolic and anabolic reactions • Metabolism : 生物體中所有化學反應之總和. • Catabolism : degradation (放能) • Anabolism : synthesis (吸能) • 能量反應 : ATP Fig. 5.1

  3. II. Enzymes • Enzymes : biocatalyst • Activation energy • Substrate, product. ex : sucrose glucose + fructose • Turnover number(TON) sucrase Enzyme 活性 : IU, SA

  4. II - 1. Naming enzymes • 字尾 ~ ase. • 分六大類 (Table 5.1)

  5. II - 2. Enzyme components • Apoenzyme + cofactor = holoenzyme cofactor 可為金屬離子 or coenzyme… • Coenzymes : 多由vitamins 衍生而來. ex : NAD+, NADP+, FMN, FAD, CoA… (Table 5.2) Fig. 5.2

  6. ex : FMN , FAD ex : NAD+ , NADP+ ex : CoQ

  7. II - 3. The mechanism of enzymatic action • 受質接觸enzyme表面之active site. • 形成enzyme-substrate complex. • Substrate 因其分子之重新排列, 其分子之降解 or 與其他受質之結合而使受質之架構改變. • Substrate product, 由 E-S complex被釋放出來. • Enzyme 本身未改變, 其可加速化學反應. “ Lock and key model ” Fig. 5.3a & 5.3b “ Induced - Fit model ”

  8. drug

  9. II - 4. Factors influencing enzymatic activity Fig. 5.4 • Temerature : denaturation • pH • Substrate conc. • Inhibitors • Feedback inhibtion(end-product inhibition) Fig. 5.5 Fig. 5.6 Fig. 5.7

  10. pH [S] Temp 雙曲線

  11. CI NCI

  12. II - 5. Ribozymes • 如enzyme般具催化功能, 對RNA具專一性. • 具較小之受質範圍.

  13. III. Energy production • Catabolic reaction • ATP

  14. III - 1. Oxidation-reduction reactions • Oxidation : 失去 e-, reduction : 得到e-. • Dehydrogenation Fig. 5.8 Fig. 5.9

  15. III - 2. The generation of ATP • 加入~p : phosphorylation • Three types : 1. Substrate-level phosphorylation 2. Oxidative phosphorylation : ETC 3. Photophosphorylation : 只發生含葉綠體且行光合作用之cell. Fig. 5.13

  16. NAD  FAD(FMN)  CoQ  Cyt  O2 H2O

  17. IV. Metabolic pathways of energy productions By-products or waste products

  18. V. Carbohydrate catabolism • Respiration & fermentation • Glucose 之respiration含 three steps : • Glycolysis • Krebs cycle • ETC Fig. 5.10

  19. V - 1. Glycolysis Fig. 5.11 • Two stages : • Preparatory stage • Energy-conserving stage

  20. V - 2. Alternatives to glycolsis • The pentose phosphate pathway(PPP) • 或稱hexose monophosphate shunt(HMS) • 形成pentose  nucleic acid; glucose; amino acid. • 產生NADPH. • 利用此pathway之微生物 : Bacillus subtilis, E.coli, Leuconostoc mesenteroides & Enterococcus faecalis.

  21. The Enter-Doudoroff pathway • G(-) : Rhizobium, Pseudomonas & Agrobacterium. G(+) 則不行pathway. • 實驗室鑑定Pseudomonas.

  22. V - 3. Cellular respiration defined • Respiratory : 物質經氧化作用產生ATP之過程, 且其最終之電子接受者為無機物者. • Aerobes, anaerobes Fig. 5.10

  23. V-3-1 Aerobic respiration • The Krebs cycle = Tricarboxylic acid cycle (TCA cycle) = Citric acid cycle • The electron transport chain (ETC) • Flavoproteins(Fp) • Cytochromes • Ubiquinones(coenzyme Q ; CoQ) Fig. 5.12 Fig. 5.13 “ Chemiosomtic mechanism ”

  24. V-3-2 The chemiosmotic mechanism of ATP generation • Chemiosmosis • Proton pump • Concentration gradient, electrical charge gradient, electrochemical gradient, potential energy… “proton motive force” • ATP synthase Fig. 5.14 Fig. 5.15

  25. V-3-3 A summary of aerobic respiration • NADH : 3 ATP, FADH2 (FMNH2) : 2 ATP • 原核cell : 38 ATP, 真核cell : 36 ATP Fig. 5.16 (Table 5.3)

  26. V-3-4 Anaerobic respiration • 最終之電子接受者異於氧氣之無機物質, ex : Pseudomonas & Bacillus --- 利用 NO3- (nitrogen cycle), Desulfovibrio --- SO4-2 H2S (sulfur cycle), 細菌 --- CO3-2 CH4

  27. V-3-5 Fermentation Fig. 5.17 • 定義 : • 由醣類 & amino acid, organic acids, purines, pyrimidines獲得能量之過程. • 不需O2參與. • 不需Krebs cycle & ETC 參與. • 以有機物質作為最終電子接受者. • 產生少量ATP, 主要能量貯存於中間產物如lactate & ethanol 中.

  28. 圖 5.17 發酵作用。小插圖顯示發酵作用與整體能量產生之關係。(a) 發酵作用，第一步驟為糖酵解作用，葡萄糖被分解為丙酮酸。第二步驟中，由糖酵解作用所產生之還原態輔酶及其相關物質 (如NADH, NADPH) 提供電子及質子給丙酮酸以形成發酵產物。(b)不同發酵作用之終產物。 於發酵作用中、ATP只於糖酵解作用中產生。

  29. V-3-5(1) Lactic acid fermentation • 首要路徑為glycolysis. Glucose  2 pyruvate 2 lactate • Lactic acid bacteria : Streptococcus & Lcatobacillus為 [homolactic or homofermentative bacteria] • 可導致食品腐敗, 但可生產 yogurt, sauerkraut & pickles. 無氧 Fig. 5.18 Fig. 5.11

  30. V-3-5(2) Alcohol fermentation 無氧 • Glucose  2 pyruvate 2 aldehyde + 2 CO2 • 酵母菌(Saccharomyces), 為 [heterolactic or heterofermentative bacteria] Fig. 5.18 2 ethanol

  31. VI. Lipid catabolism • Fat : fatty acids + glycerol • 微生物可利用lipase將脂肪分解為fatty acids & glycerol  TCA cycle Fig. 5.20

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