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Chapter 4
Microbial Metabolism
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Metabolism
Catabolism (分解代谢)
• Breakdown of
complex organic
compounds into
simpler ones
Anabolism (合成代谢)
• Building of complex
organic compounds
from simpler ones
• Generally hydrolytic
reactions (水解反应)
• Involve dehydration
synthesis reactions(脱
水/缩合反应)
• Exergonic (产能)
• Endergonic (耗能)
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Metabolism in perspective
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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)
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Enzymatic reaction
Sucrase 蔗糖酶
glucose
Sucrose
蔗糖
葡萄糖
+
fructose
果糖
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Enzyme components
底物
脱辅基酶蛋白
辅酶
全酶
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Activation energy
Activation energy: amount of energy needed to
disrupt stable molecule so that reaction can take place
能量水平
底物
酶促反
应所需
活化能
非酶促
反应所
需活化
能
产物
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Enzymatic reaction steps
活性位点
1.
2.
3.
4.
5.
酶-底物复合体
Substrate approaches active site
Enzyme-substrate complex forms
Substrate transformed into products
Products released
Enzyme recycled
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Factors Affecting Enzyme Activity
1. Temp
2. pH
3. Substrate concentration
4. Inhibitors
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Enzyme inhibitor action
Competitive Non-competitive
Inhibition
Inhibition
变象位点
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Energy Production
Oxidation-Reduction Reactions
Redox reaction = oxidation-reduction pair of reactions
Oxidation: removal of electrons from molecule
Reduction: gaining of 1+ electrons
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Energy Production
生物体内的
电子载体
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)
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Energy Production
ATP（三磷酸腺苷）
腺嘌呤
核糖
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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
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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
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Carbohydrate Catabolism
Carbohydrate catabolism: breakdown of carbohydrates
to produce Energy.
There are two types of carbohydrate catabolism:
1 Respiration
2 Fermentation
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Respiration
and
Fermentation
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Glycolysis
Initial stage
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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
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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
2 pyruvate
2 Acetyl CoA
3 carbons each
2 carbons each
decarboxylation
Krebs cycle produces
from every 2 Acetyl CoA:
4 CO2
6 NADH
2 FADH2
2 ATP
FAD: 黄素腺嘌呤二核苷酸
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When FAD
(oxidized form) is
reduced, two H
atoms are added
directly to produce
FADH2 (reduced
form)
Details of Krebs Cycle
Substrate level
phosphorylation
What is FAD?
It is called 黄素腺嘌
呤二核苷酸
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Electron Transport Chain
Electron Transport Chain is a series of electron carriers that
transfer electrons from donors (NADH, FADH2) to electron
acceptors (O2)
Bacteria
Eucaryotes
It is located
Plasma membrane
Inner membrane of mitochondria
Oxidative phosphorylation: process by which energy from
electron transport is used to make ATP
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Location of electron transport chain in eukaryotes
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Electron Transport Chain
What is cytochromes?
黄素单
核苷酸
泛醌
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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.
Amino
acidamino
acid
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Electron Transport Chain
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Creation of Proton
Motive Force (PMF)
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.
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Electron Transport Chain
1个NADH产生3个ATP
Oxidative phosphorylation
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Yield of
ATP in
Glycolysis
& Aerobic
Respiration
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Glycolytic Pathway(糖酵解途径)
Substrate-level phosphorylation (ATP)
Oxidative phosphorylation w/ 2 NADH
2 ATP
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)
Oxidative phosphorylation w/ 6 NADH
Oxidative phosphorylation w/ 2 FADH2
Total
2 ATP
18 ATP
4 ATP
38 ATP
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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
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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+
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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)
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Fermentation
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Nutritional Patterns
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Nutritional Requirements
1. Photolithotrophic autotrophs
Light
Inorganic H+ source
CO2 carbon source
2. Photoorganotrophic heterotrophs
Light energy
Organic H+ source
Organic carbon source
3. Chemolithotrophic autotrophs
Chemical energy source
Inorganic H+ source
CO2 Carbon source
4. Chemoorganotrophic heterotrophs
Chemical energy source
Organic H+ source
Organic carbon source
photolithoautotroph (光能自养)
photoorganoheterotroph (光能异养)
chemolithoautotroph (化能自养)
chemoorganoheterotroph (化能异养)
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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
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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
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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
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Construction of Cells
Cells
Organelles(细胞器)
Supramolecular systems
Macromolecules
Monomers
Inorganic molecules