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Chapter 4

Chapter 4. Microbial Metabolism. Breakdown of complex organic compounds into simpler ones Generally hydrolytic reactions ( 水解反应 ) Exergonic ( 产能 ). Building of complex organic compounds from simpler ones Involve dehydration synthesis reactions( 脱水 / 缩合反应 ) Endergonic ( 耗能 ). Metabolism.

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Chapter 4

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  1. Chapter 4 Microbial Metabolism

  2. Breakdown of complex organic compounds into simpler ones Generally hydrolytic reactions (水解反应) Exergonic (产能) Building of complex organic compounds from simpler ones Involve dehydration synthesis reactions(脱水/缩合反应) Endergonic (耗能) Metabolism Catabolism (分解代谢) Anabolism (合成代谢)

  3. Metabolism in perspective

  4. Enzymes Catabolism and anabolism are all mediated by enzymes, which are proteins produced by living cells that catalyze (催化) chemical reactions by lowering the activation energy (活化能) required to start a reaction • Enzymes have specificity (专一性) • Each enzyme catalyzes only one reaction • Enzymes are very efficient-increase reaction rate by 108-1010 times • Turnover number(周转数): maximum no. of substrate molecules converted to product per second (单位时间内转变成产物的底物摩尔数)

  5. Enzymatic reaction Sucrase 蔗糖酶 葡萄糖 glucose Sucrose + 蔗糖 fructose 果糖

  6. Enzyme components 底物 辅酶 脱辅基酶蛋白 全酶

  7. Activation energy Activation energy:amount of energy needed to disrupt stable molecule so that reaction can take place 底物 非酶促反应所需活化能 能量水平 酶促反应所需活化能 产物

  8. Enzymatic reaction steps 酶-底物复合体 活性位点 1. Substrate approaches active site 2. Enzyme-substrate complex forms 3. Substrate transformed into products 4. Products released 5. Enzyme recycled

  9. Factors Affecting Enzyme Activity 1. Temp 2. pH 3. Substrate concentration 4. Inhibitors

  10. Enzyme inhibitor action Non-competitive Inhibition Competitive Inhibition 变象位点

  11. Energy ProductionOxidation-Reduction Reactions Redox reaction = oxidation-reduction pair of reactions Oxidation: removal of electrons from molecule Reduction: gaining of 1+ electrons

  12. Energy Production NAD: 烟酰胺腺嘌呤二核苷酸(辅酶I) 生物体内的 电子载体 NADP: 烟酰胺腺嘌呤二核苷酸磷酸(辅酶II) 含有2个H原子的有机分子

  13. Energy ProductionATP（三磷酸腺苷） 腺嘌呤 核糖

  14. Role of ATP in Metabolism 1. ATP is a high-energy molecule: a. It breaks down almost completely b. Removing terminal phosphate causes large negative change in free energy c. Releases large amount of energy 2. ATP is energy currency of the cell 3. ATP has high phosphate group transfer potential 4. ATP is a coupling agent in the cell: links exergonic reactions to endergonic reactions

  15. Energy Production Three mechanisms of phosphorylation to generate ATP: 1. Substrate-level phosphorylation 2. Oxidative phosphorylation 3. Photophosphorylation Substrate level phosphorylation: synthesis of ATP by donation of P on carbon #1 (phosphorylated organic compound) to ADP. Oxidative phosphorylation: process by which energy from electron transport is used to make ATP Photophosphorylation: process by which light energy is used to make ATP

  16. Carbohydrate Catabolism Carbohydrate catabolism:breakdown of carbohydrates to produce Energy. There are two types of carbohydrate catabolism: 1 Respiration 2 Fermentation

  17. Respiration andFermentation

  18. Glycolysis Initial stage

  19. Substrate level phosphorylation Glycolysis ATP producing stage 每1个葡萄糖产生4个ATP，但是消耗2个ATP，净产生2个ATP

  20. Krebs Cycle Krebs Cycle (TCA cycle, citric acid cycle三羧酸循环): series of redox reactions in which potential energy stored in acetyl CoA (乙酰辅酶A)is released step by step Krebs cycle produces from every 2 Acetyl CoA: 4 CO2 6 NADH 2 FADH2 2 ATP 2 pyruvate 3 carbons each 2 Acetyl CoA 2 carbons each decarboxylation FAD: 黄素腺嘌呤二核苷酸

  21. Substrate level phosphorylation What is FAD? It is called 黄素腺嘌 呤二核苷酸 Details of Krebs Cycle When FAD (oxidized form) is reduced, two H atoms are added directly to produce FADH2 (reduced form)

  22. Electron Transport Chain Electron Transport Chain is a series of electron carriers that transfer electrons from donors (NADH, FADH2) to electron acceptors (O2) It is located Bacteria Plasma membrane Eucaryotes Inner membrane of mitochondria Oxidative phosphorylation: process by which energy from electron transport is used to make ATP

  23. Location of electron transport chain in eukaryotes

  24. Electron Transport Chain What is cytochromes? 黄素单核苷酸 泛醌

  25. Amino acid-amino acid Cytochromes are proteins with iron-containing porphyrin (heme) prosthetic groups attached to them When heme groups (oxidized form) in cyt molecules are reduced, single electrons are added directly the central iron atom, converting Fe+++ (oxidized form) to Fe++(reduced form). Heme groups do not accept protons.

  26. Electron Transport Chain

  27. ATP synthaseprotein complex contains only channels for proton entry. As protons push in through channel, the base rotates. Specific binding sites allow ADP + Pi    ATP. Creation of Proton Motive Force (PMF)

  28. Electron Transport Chain Oxidative phosphorylation 1个NADH产生3个ATP

  29. Yield of ATP in Glycolysis & Aerobic Respiration

  30. Glycolytic Pathway(糖酵解途径) Substrate-level phosphorylation (ATP) 2 ATP Oxidative phosphorylation w/ 2 NADH 6 ATP 2 Pyruvate to 2 Acetyl CoA(丙酮酸到乙酰辅酶A) Oxidative phosphorylation w/2 NADH 6 ATP Tricarboxylic Acid Cycle(三羧酸循环) Substrate-level phosphorylation (GTP) 2 ATP Oxidative phosphorylation w/ 6 NADH 18 ATP Oxidative phosphorylation w/ 2 FADH2 4 ATP Total 38 ATP

  31. Anaerobic Respiration Anaerobic respiration: energy-yielding process in which terminal electron acceptor is oxidized inorganic compound other than oxygen • Major electron acceptors = Nitrate, sulfate, CO2, Iron • Anaerobic respiration produces less ATP • Anaerobic respiration is more efficient than fermentation • Uses ETC & oxidative phosphorylation in absence of O2

  32. Fermentation Fermentation: energy-yielding process in which organic molecules serve as both e donors and e acceptors. It 1. releases energy from organic molecules 2. does not require oxygen, but sometimes can occur in its presence 3. does not require use of the Krebs cycle or ETC 4. uses organic molecule as final electron acceptor (pyruvic acid or its derivatives) 5. produces small amounts of ATP 6. is needed to recycle NAD+

  33. Examples of Fermentation Alcoholic fermentations ethanol and CO2 Lactic acid fermentations lactic acid (lactate) Formic acid fermentation mixed acids or butanediol ethanol (乙醇) lactic acid (乳酸lactate) mixed acids (混合酸)or butanediol (丁二醇) Formic acid (甲酸/蚁酸)

  34. Fermentation

  35. Nutritional Patterns

  36. Nutritional Requirements 1. Photolithotrophic autotrophs photolithoautotroph (光能自养) Light Inorganic H+ source CO2 carbon source 2. Photoorganotrophic heterotrophs photoorganoheterotroph (光能异养) Light energy Organic H+ source Organic carbon source 3. Chemolithotrophic autotrophs chemolithoautotroph (化能自养) Chemical energy source Inorganic H+ source CO2 Carbon source 4. Chemoorganotrophic heterotrophs chemoorganoheterotroph (化能异养) Chemical energy source Organic H+ source Organic carbon source

  37. Nutritional Requirements If an organism uses light as an energy source, organic substances for an electron source and organic substances for a carbon source, what is it called? Energy sources: Photo Chemo Hydrogen sources: Litho Organo Carbon sources: Auto Hetero Photoorganoheterotroph

  38. AnabolismMetabolic Pathways of Energy Use 1. Polysaccharide biosynthesis 2. Lipid biosynthesis 3. Amino acid biosynthesis 4. Protein biosynthesis 5. Purine & pyrimidine biosynthesis **Primary use of lipids in cells = component of bacterial membranes

  39. Use of Energy in Biosynthesis Anabolism: the creation of order by the synthesis of complex molecules from simpler ones with the input of energy Turnover: the continual degradation and resynthesis of cellular constituents *Most ATP is used in protein synthesis *Anabolism requires a lot of energy

  40. Construction of Cells Cells Organelles(细胞器) Supramolecular systems Macromolecules Monomers Inorganic molecules

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