Shixue Yin (Prof Dr) Chapter 4 Microbial Metabolism

Shixue Yin (Prof Dr)

Chapter 4

Microbial Metabolism


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


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 )


Enzymatic reaction

Sucrose

glucose

fructose

+

Sucrase 蔗糖酶

蔗糖

葡萄糖

果糖


Enzyme components

脱辅基酶蛋白辅酶全酶

底物


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


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


Factors Affecting Enzyme Activity

1. Temp

2. pH

3. Substrate concentration

4. Inhibitors


Enzyme inhibitor action

Competitive Inhibition

Non-competitive Inhibition

变象位点


Energy ProductionOxidation-Reduction Reactions

Redox reaction = oxidation-reduction pair of reactions

Oxidation: removal of electrons from moleculeReduction: gaining of 1+ electrons


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


Energy ProductionATP（三磷酸腺苷）

腺嘌呤

核糖


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


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


Carbohydrate Catabolism

Carbohydrate catabolism: breakdown of carbohydrates to produce Energy.

There are two types of carbohydrate catabolism:

1 Respiration

2 Fermentation


Respiration and

Fermentation


Glycolysis

Initial stage


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


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


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


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


Location of electron transport chain in eukaryotes



黄素单核苷酸泛醌

What is cytochromes?


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




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)



Oxidative phosphorylation1 个 NADH产生 3 个ATP


Yield of ATP in Glycolysis & Aerobic Respiration


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


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


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+


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 )


Fermentation



Nutritional Patterns


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


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?


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


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


Construction of Cells

Inorganic molecules

Monomers

Macromolecules

Supramolecular systems

Organelles(细胞器 )

Cells

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Shixue Yin (Prof Dr) Chapter 4 Microbial Metabolism