Shixue Yin (Prof Dr) Chapter 4 Microbial Metabolism

Shixue Yin (Prof Dr) 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 ) Catabolism ( 分解代谢 ) Anabolism ( 合成代谢 )

Shixue Yin (Prof Dr) Metabolism in perspective

Shixue Yin (Prof Dr) 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 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 )

Shixue Yin (Prof Dr) Enzymatic reaction Sucrose glucose fructose + Sucrase 蔗糖酶 蔗糖 葡萄糖 果糖

Shixue Yin (Prof Dr) Enzyme components 脱辅基酶蛋白 辅酶 全酶 底物

Shixue Yin (Prof Dr) Activation energy Activation energy: amount of energy needed to disrupt stable molecule so that reaction can take place 底物 产物 能量水平 非酶促 反应所 需活化 能 酶促反 应所需 活化能

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

Shixue Yin (Prof Dr) Factors Affecting Enzyme Activity 1. Temp 2. pH 3. Substrate concentration 4. Inhibitors

Shixue Yin (Prof Dr) Enzyme inhibitor action Competitive Inhibition Non-competitive Inhibition 变象位点

Shixue Yin (Prof Dr) Energy Production Oxidation-Reduction Reactions Redox reaction = oxidation-reduction pair of reactions Oxidation: removal of electrons from molecule Reduction: gaining of 1+ electrons

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

Shixue Yin (Prof Dr) Energy Production ATP （三磷酸腺苷） 腺嘌呤 核糖

Shixue Yin (Prof Dr) 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

Shixue Yin (Prof Dr) 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

Shixue Yin (Prof Dr) Carbohydrate Catabolism Carbohydrate catabolism: breakdown of carbohydrates to produce Energy. There are two types of carbohydrate catabolism: 1 Respiration 2 Fermentation

Shixue Yin (Prof Dr) Respiration and Fermentation

Shixue Yin (Prof Dr) Glycolysis Initial stage

Shixue Yin (Prof Dr) Glycolysis ATP producing stage Substrate level phosphorylation 每 1 个葡萄糖产生 4 个 ATP ，但是消耗 2 个 ATP ，净产生 2 个 ATP

Shixue Yin (Prof Dr) 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 CO 2 6 NADH 2 FADH 2 2 ATP 2 Acetyl CoA 2 carbons each 2 pyruvate 3 carbons each decarboxylation FAD: 黄素腺嘌呤二核苷酸

Shixue Yin (Prof Dr) Substrate level phosphorylation When FAD (oxidized form) is reduced, two H atoms are added directly to produce FADH 2 (reduced form) Details of Krebs Cycle What is FAD? It is called 黄素腺嘌 呤二核苷酸

Shixue Yin (Prof Dr) Electron Transport Chain Electron Transport Chain is a series of electron carriers that transfer electrons from donors (NADH, FADH 2 ) to electron acceptors (O 2 ) It is located BacteriaPlasma membrane EucaryotesInner membrane of mitochondria Oxidative phosphorylation: process by which energy from electron transport is used to make ATP

Shixue Yin (Prof Dr) Location of electron transport chain in eukaryotes

Shixue Yin (Prof Dr) Electron Transport Chain 黄素单 核苷酸 泛醌 What is cytochromes?

Shixue Yin (Prof Dr) 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. Cytochromes are proteins with iron-containing porphyrin (heme) prosthetic groups attached to them Amino acid- amino acid

Shixue Yin (Prof Dr) Electron Transport Chain

Shixue Yin (Prof Dr) ATP synthase protein complex contains only channels for proton entry. As protons push in through channel, the base rotates. Specific binding sites allow ADP + P i ATP. Creation of Proton Motive Force (PMF)

Shixue Yin (Prof Dr) Electron Transport Chain Oxidative phosphorylation 1 个 NADH 产生 3 个 ATP

Shixue Yin (Prof Dr) Yield of ATP in Glycolysis & Aerobic Respiration

Shixue Yin (Prof Dr) Glycolytic Pathway( 糖酵解途径 ) Substrate-level phosphorylation (ATP)2 ATP Oxidative phosphorylation w/ 2 NADH6 ATP 2 Pyruvate to 2 Acetyl CoA( 丙酮酸到乙酰辅酶 A) Oxidative phosphorylation w/2 NADH6 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 FADH 2 4 ATP Total 38 ATP

Shixue Yin (Prof Dr) Anaerobic Respiration Anaerobic respiration: energy-yielding process in which terminal electron acceptor is oxidized inorganic compound other than oxygen Major electron acceptors = Nitrate, sulfate, CO 2, Iron Anaerobic respiration produces less ATP Anaerobic respiration is more efficient than fermentation Uses ETC & oxidative phosphorylation in absence of O 2

Shixue Yin (Prof Dr) 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 +

Shixue Yin (Prof Dr) Examples of Fermentation Alcoholic fermentations ethanol and CO 2 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 )

Shixue Yin (Prof Dr) Fermentation

Shixue Yin (Prof Dr)

Nutritional Patterns

Shixue Yin (Prof Dr) Nutritional Requirements 1. Photolithotrophic autotrophsphotolithoautotroph ( 光能自养 ) Light Inorganic H+ source CO2 carbon source 2. Photoorganotrophic heterotrophsphotoorganoheterotroph ( 光能异养 ) Light energy Organic H+ source Organic carbon source 3. Chemolithotrophic autotrophschemolithoautotroph ( 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

Shixue Yin (Prof Dr) Nutritional Requirements Carbon sources: Auto Hetero Energy sources: Photo Chemo Hydrogen sources: Litho Organo Photoorganoheterotroph 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?

Shixue Yin (Prof Dr) Anabolism Metabolic 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

Shixue Yin (Prof Dr) 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

Shixue Yin (Prof Dr) Construction of Cells Inorganic molecules Monomers Macromolecules Supramolecular systems Organelles( 细胞器 ) Cells