MicrobialMetabolism:Catabolic andAnabolicPathways
Chapter 8(p. 211-231)
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Learning Objectives:
•Explain the overall function of metabolic pathway
•Describe the chemical reactions in glycolysis
•Explain the products of the Krebs cycle
•Describe the chemiosmotic model for ATP generation
•Compare and contrast aerobic and anaerobic respiration
•Describe the chemical reactions and list some products offermentation.
•Describe how lipids and proteins undergo catabolism
•Define amphibolic pathways
•Contrast oxygenic and anoxygenic photosynthesis.
Metabolic Pathways
Carbohydrate Catabolism
•The breakdown of carbohydrates to releaseenergy
•Glycolysis
•Krebs cycle
•Electron transport chain
Glycolysis
•Oxidation of glucose to pyruvic acid
•Produces ATP and NADH.
1
3
4
5
PreparatoryStage
•Two ATPs areused
•Glucose is splitto form twophosphorylated3-carbon sugars
9
Energy-ConservingStage
•Two 3-carbon sugarsoxidized to twoPyruvic acidmolecules
•Four ATP produced(substrate levelphosphorylation)
•Two NADH produced
Glycolysis Summary
•One glucose is used
•Partial oxidation of the sugar, 2 pyruvates areend products
•Two NADH are reduced
•2 ATP are consumed, 4 ATP total are made, netof 2 ATP produced
Intermediate Step
•Pyruvic acid (fromglycolysis) is oxidizedand decarboxylated.
Krebs Cycle
Complete oxidationof acetyl CoA to CO2produces NADH andFADH2.
Krebs Cycle Summary
Pyruvate 1
•3 CO2
•4 NADH
•1 FADH2
•1 ATP
Pyruvate 2
•3 CO2
•4 NADH
•1 FADH2
•1 ATP
•Glucose has now been completely oxidized tocarbon dioxide
•Electrons are temporarily on carrier molecules
•2 ATP total made by substrate level phosphorylation
The Electron Transport Chain
•A series of carrier molecules that are, in turn,oxidized and reduced as electrons are passeddown the chain.
•Energy released can be used to produce ATP bychemiosmosis.
Electron Transport System
•NADH oxidized
•Electrons passthrough membranecarriers
•Protons pumped out(work is done)
•Electrons accepted byan inorganic molecule
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Cell wall
Cytochromes
Cytoplasm
Cellmembrane
with ETS
ATP
ADP
ATP synthase
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Aerobic Respiration
•The electron acceptor is an oxygen
•This is a very good acceptor
•Yields water upon reduction
•Because so much energy is released, the cellcan pump out about 10 protons
•Occurs in bacterial membrane andmitochondria of eukaryotes
Anaerobic Respiration
•The electron acceptor is not oxygen
•Examples: nitrate, nitrite, and sulfate
•These are mediocre acceptors – not as good asoxygen
•Yields other inorganic molecules upon reduction
•Less favorable reactions pump out fewer protons
Electron acceptor
Products
NO3–
NO2–, N2 + H2O
SO4–
H2S + H2O
CO32 –
CH4 + H2O
Anaerobic Respiration
Chemiosmosis
•Proton gradient ispotential energy
•Allowing protonsback into the cellcan be coupled towork
•3 protons enteringdrive the synthesisof 1 ATP
•Oxidativephosphorylation
Aerobic Respiration Yield
•1 Glucose 6 CO2
•2 ATP from glycolysis
•2 NADH from glycolysis 6 ATP
•2 ATP from Krebs cycle substrate level
•8 NADH from Krebs cycle 24 ATP
•2 FADH2 from Krebs cycle 4 ATP
•Total 36-38 ATP per glucose
Fermentation
•Performed by anaerobic microorganisms
•Does not use Krebs cycle or ETC
•Primary purpose: Regenerate NAD for reuse
•The electron acceptor is an organic molecule
•Secondary purpose: Generate additionalenergy
•Energy yields are very small
Fermentation
•NADH oxidized
•Organic moleculereduced
•Many possible endproducts
•Lactic acid
•Ethanol
•Vinegar
•Acetone
C
C
O
O
C
H
H
H
OH
C
C
H
H
H
H
H
C
C
O
H
H
H
H
C
C
C
H
H
H
H
O H
O
O
H
System: Homolactic bacteria;
human muscle
Glucose
System:Yeasts
Glycolysis
Lactic acid
Ethyl alcohol
Pyruvic acid
OH
NADH
NAD H
NADH
NAD
NAD
CO2
Acetaldehyde
O2 is final electron
acceptor.
ATP produced = 38
ATP produced = 2 to 36
ATP produced = 2
Non oxygen electron acceptors(examples: SO42–, NO3–, CO32– )
An organic molecule is final
electron accept or (pyruvate,
acetaldehyde, etc.).
AEROBIC RESPIRATION
Glycolysis
Glucose
ATP
NADH
2pyruvate
(3C)
(6C)
CO2
Acety lCoA
FADH2
NADH
ATP
Krebs
CO2
Electrons
Electron transport
ANAEROBIC RESPIRATION
Glycolysis
Glucose
ATP
NADH
2pyruvate
(3C)
(6C)
CO2
Acety lCoA
FADH2
NADH
ATP
Krebs
CO2
Electrons
Electron transport
FERMENTATION
CO2
Glycolysis
Glucose
ATP
NADH
2pyruvate
Lactic acid
Ethanol
Or other alcohols,
acids, gases
Acetaldehyde
(6C)
(3C)
Fermentation
Fermentation
•Alcohol fermentation: Produces ethyl alcohol +CO2.
•Lactic acid fermentation: Produces lactic acid.
•Homolactic fermentation: Produces lactic acidonly.
•Heterolactic fermentation: Produces lactic acidand other compounds.
Pathway
Eukaryote
Prokaryote
Glycolysis
Cytoplasm
Cytoplasm
Intermediate step
Cytoplasm
Cytoplasm
Krebs cycle
Mitochondrial matrix
Cytoplasm
ETC
Mitochondrial innermembrane
Plasmamembrane
Lipid Catabolism
Figure 5.20
Protein
Amino acids
Extracellular proteases
Krebs cycle
Deamination, decarboxylation, dehydrogenation
Organic acid
Protein Catabolism
Amphibolism
CO2
H2O
Glycolysis
Anabolism
Catabolism
Simple
products
Metabolic
pathways
Building block
Macromolecule
Cell
structure
Chromosomes
Enzymes
Membranes
Cell wall
Storage
Membranes
Storage
Lipids
Fats
Starch
Cellulose
Proteins
Nucleic
acids
Nucleotides
Amino acids
Carbohydrates
Fatty acids
Beta oxidation
Deamination
GLUCOSE
Pyruvic acid
Krebs
cycle
Acetyl coenzyme A
NH3
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Photosynthesis
•Photo: Conversion of light energy into chemicalenergy (ATP)
•Light-dependent (light) reactions
•Synthesis: Fixing carbon into organic molecules
•Light-independent (dark) reaction, Calvin-Bensoncycle
Oxygenic Photosynthesis
•Chlorophyll pigments
•Thylakoid membrane
•Capture light energy
•Electron transport
•Photophosphorylation
•Makes NADH and ATP
•Oxygen produced
•Algae, plants, andcyanobacteria
Anoxygenic Photosynthesis
•Purple bacteria (similar to photosystem II)
•Make ATP
•Can’t make NADH
•No oxygen produced
•Green bacteria (similar to photosystem I)
•Make ATP
•Also make NADH
•No oxygen produced
Calvin Benson Cycle
•Fix carbon dioxide
•Autotrophs
•Reverse of glycolysis
•6 CO2 Glucose
P
P
P
P
P
P
P
P
P
P
P
P
P
P
H
H
Splitting
ADP
ATP × 2
ADP
ATP
Series of 7 Carbon
and 5 Carbon
intermediates
Ribulose-1,5-bisphosphate
5Carbon
CO2
6 Carbon
intermediate
NADPH × 2
NADP
Glyceraldehyde-3
phosphate
Glucose
Fructose intermediates
1,3-bisphosphoglyceric acid
Calvin Cycle
3-phosphoglyceric
acid
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