shixue yin (prof dr) chapter 4 microbial metabolism
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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)
EnzymesCatabolism 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 )
Shixue Yin (Prof Dr)
Activation energyActivation 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 site2. Enzyme-substrate complex forms3. Substrate transformed into products4. Products released5. 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)
Energy ProductionOxidation-Reduction Reactions
Redox reaction = oxidation-reduction pair of reactions
Oxidation: removal of electrons from moleculeReduction: 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)
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 ProductionThree mechanisms of phosphorylation to generate ATP:1. Substrate-level phosphorylation2. Oxidative phosphorylation3. 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)
GlycolysisATP 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 CycleKrebs 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 producesfrom every 2 Acetyl CoA:
4 CO2
6 NADH2 FADH2
2 ATP
2 Acetyl CoA2 carbons each
2 pyruvate3 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 FADH2 (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, FADH2) to electron acceptors (O2)
It is located Bacteria Plasma membraneEucaryotes Inner membrane of mitochondria
Oxidative phosphorylation: process by which energy from electron transport is used to make ATP
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
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ATP synthase protein 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)
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Glycolytic Pathway(糖酵解途径 )
Substrate-level phosphorylation (ATP) 2 ATPOxidative 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 ATPOxidative phosphorylation w/ 6 NADH 18 ATPOxidative phosphorylation w/ 2 FADH2 4 ATP
Total 38 ATP
Shixue Yin (Prof Dr)
Anaerobic RespirationAnaerobic 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
Shixue Yin (Prof Dr)
FermentationFermentation: 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 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 )
Shixue Yin (Prof Dr)
Nutritional Requirements
1. Photolithotrophic autotrophs photolithoautotroph (光能自养 )LightInorganic H+ sourceCO2 carbon source
2. Photoorganotrophic heterotrophs photoorganoheterotroph (光能异养 )Light energyOrganic H+ sourceOrganic carbon source
3. Chemolithotrophic autotrophs chemolithoautotroph (化能自养 )Chemical energy sourceInorganic H+ sourceCO2 Carbon source
4. Chemoorganotrophic heterotrophs chemoorganoheterotroph (化能异养 )Chemical energy sourceOrganic H+ sourceOrganic 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)
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
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