microbial metabolism: catabolic and anabolic pathways chapter 8 (p. 211-231) copyright © the...
TRANSCRIPT
Microbial Metabolism:
Catabolic and Anabolic Pathways
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 of fermentation.
• Describe how lipids and proteins undergo catabolism
• Define amphibolic pathways
• Contrast oxygenic and anoxygenic photosynthesis.
Metabolic Pathways
Carbohydrate Catabolism
• The breakdown of carbohydrates to release energy
• Glycolysis
• Krebs cycle
• Electron transport chain
Glycolysis
• Oxidation of glucose to pyruvic acid
• Produces ATP and NADH.
1
3
4
5
Preparatory Stage
• Two ATPs are used
• Glucose is split to form two phosphorylated 3-carbon sugars
9
Energy-Conserving
Stage• Two 3-carbon sugars
oxidized to two Pyruvic acid molecules
• Four ATP produced (substrate level phosphorylation)
• Two NADH produced
Glycolysis Summary
• One glucose is used
• Partial oxidation of the sugar, 2 pyruvates are end products
• Two NADH are reduced
• 2 ATP are consumed, 4 ATP total are made, net of 2 ATP produced
Intermediate Step
• Pyruvic acid (from glycolysis) is oxidized and decarboxylated.
Krebs Cycle
Complete oxidation
of acetyl CoA to CO2
produces NADH and
FADH2.
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 to
carbon 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 passed down the chain.
• Energy released can be used to produce ATP by chemiosmosis.
Electron Transport System
• NADH oxidized
• Electrons pass through membrane carriers
• Protons pumped out (work is done)
• Electrons accepted by an inorganic molecule
H
HH H
H
HH
H H
HH HH
HHH
HH
H H
Cell wall
Cytochromes
Cytoplasm
Cell membranewith 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 cell can pump out about 10 protons
• Occurs in bacterial membrane and mitochondria of eukaryotes
Anaerobic Respiration
• The electron acceptor is not oxygen
• Examples: nitrate, nitrite, and sulfate
• These are mediocre acceptors – not as good as oxygen
• 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 is potential energy
• Allowing protons back into the cell can be coupled to work
• 3 protons entering drive the synthesis of 1 ATP
• Oxidative phosphorylation
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 additional energy
• Energy yields are very small
Fermentation
• NADH oxidized
• Organic molecule reduced
• Many possible end products
• Lactic acid
• Ethanol
• Vinegar
• Acetone
C C
OO
C
H
H
H
OHC C
H
H
H
H
H
C C
O
H
H
H
H
CC C
H
H
H
H
O HO
OH
System: Homolactic bacteria;human muscle
Glucose
System: Yeasts
Glycolysis
Lactic acidEthyl alcohol
Pyruvic acid
OH
NADH
NAD HNADH
NAD
NAD
CO2
Acetaldehyde
O2 is final electronacceptor.
ATP produced = 38 ATP produced = 2 to 36 ATP produced = 2
Non oxygen electron acceptors (examples: SO4
2–, NO3–, CO3
2– )
An organic molecule is finalelectron 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 acid only.
• Heterolactic fermentation: Produces lactic acid and other compounds.
Pathway Eukaryote Prokaryote
Glycolysis Cytoplasm Cytoplasm
Intermediate step Cytoplasm Cytoplasm
Krebs cycle Mitochondrial matrix Cytoplasm
ETC Mitochondrial inner membrane
Plasma membrane
Lipid Catabolism
Figure 5.20
Protein Amino acidsExtracellular proteases
Krebs cycleDeamination, decarboxylation, dehydrogenation
Organic acid
Protein Catabolism
Amphibolism
CO2
H2O
Gly
co
lys
is
An
ab
oli
sm
Ca
tab
oli
sm
Simpleproducts
Metabolicpathways
Building block
Macromolecule
Cellstructure
Chromosomes EnzymesMembranes
Cell wallStorage
MembranesStorage
LipidsFats
StarchCellulose
ProteinsNucleicacids
Nucleotides Amino acids Carbohydrates Fatty acids
Beta oxidationDeamination
GLUCOSE
Pyruvic acid
Krebscycle
Acetyl coenzyme A
NH3
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Photosynthesis
• Photo: Conversion of light energy into chemical energy (ATP)
• Light-dependent (light) reactions
• Synthesis: Fixing carbon into organic molecules
• Light-independent (dark) reaction, Calvin-Benson cycle
Oxygenic Photosynthesis
• Chlorophyll pigments
• Thylakoid membrane
• Capture light energy
• Electron transport
• Photophosphorylation
• Makes NADH and ATP
• Oxygen produced
• Algae, plants, and cyanobacteria
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
PP
PP
P P
P P
PP
P
PH
H
Splitting
ADP
ATP × 2
ADP
ATP
Series of 7 Carbonand 5 Carbonintermediates
Ribulose-1,5-bisphosphate5Carbon
CO2
6 Carbonintermediate
NADPH × 2
NADP
Glyceraldehyde-3phosphate
Glucose
Fructose intermediates
1,3-bisphosphoglyceric acid
Calvin Cycle
3-phosphoglycericacid
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