Download Microbiology pathways

Microbe of the Week
Pseudomonas aeruginosa
The Genus Pseudomonas….
 Gram negative obligate free-living
aerobic organisms, often in water
 Can oxidize many organic
compounds to obtain energy
 Pseudomonas aeruginosa is a
human pathogen
Microbe of the Week
Pseudomonas aeruginosa
An opportunistic pathogen from the
environment, infecting:
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Burn patients
Cystic fibrosis patients
Immuno-compromised patients
Medically compromised hospitalized patients
A naturally antibiotic-resistant organism
Pseudomonas aeruginosa
An opportunistic pathogen from the
HOT TUB !
Causing Folliculits
Microbial Metabolism
Cellular Respiration and
Fermentation
What happens after glycolysis?
What happens after glycolysis?

After glucose is broken down to pyruvic
acid, pyruvic acid can be channeled into
either

Aerobic Respiration OR Fermentation

Aerobic respiration

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Uses the TCA cycle and electron transport chain
Final electron acceptor is O2
Anaerobic respiration

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Uses the TCA cycle and only PART of the electron
transport chain
Final electron acceptor is an inorganic molecule other
than O2, like nitrate or sulfate.
Aerobic Respiration

Tricarboxylic acid (TCA) cycle
Kreb’s cycle or citric acid cycle
 A large amount of potential energy stored in
acetyl CoA is released by a series of redox
reactions that transfer electrons to the
electron carrier coenzymes (NAD+ and FAD)

Acetyl CoA

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Where does it come from?
Pyruvic acid, from glycolysis, is converted
to a 2-carbon (acetyl group) compound
(decarboxylation)
The acetyl group then
combines with
Coenzyme A through a
high energy bond
NAD+ is reduced to
NADH
TCA cycle
Pyruvate
NAD+
CoA

For every
molecule of
glucose (2 acetyl
CoA) the TCA
cycle generates

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4 CO2
6 NADH
2 FADH2
2 ATP
NADH
CO2
CoA
Acetyl-CoA
CoA
NADH
Oxaloacetate
Citrate
NAD+
Isocitrate
NAD+
Malate
NADH
CO2
H2O
Fumarate
a-ketoglutarate
NAD+
FADH2
CoA
P
FAD
Succinate
CoA
ATP
NADH
CoA
Succinyl-CoA
ADP
CO2
Where to now?

All the reduced coenzyme electron carriers
make their way to the electron transport
chain
2 NADH from glycolysis
 2 NADH from pyruvic acid to acetyl CoA
conversion
 6 NADH and 2 FADH2 from the TCA cycle


The electron transport chain indirectly
transfers the energy from these
coenzymes to ATP
The electron transport chain

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Sequence of carrier molecules capable of
oxidation and reduction
Electrons are passed down the chain in a
sequential and orderly fashion
Energy is released from the flow of electrons
down the chain
This release of energy is coupled to the
generation ATP by oxidative phosphorylation
Membrane location of the ETC

The electron transport chain is located in
the inner membrane of the mitochondria of
eukaryotes
 the plasma membrane of prokaryotes

The ETC players
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Three classes of ETC carrier molecules
Flavoproteins
Contain a coenzyme derived from riboflavin
 Capable of alternating oxidations/reductions
 Flavin mononucleotide (FMN)
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Cytochromes
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Have an iron-containing group (heme) which
can exist in alternating reduced (Fe2+) and
oxidized (Fe3+) forms
Coenzyme Q (Ubiquinone)

Small non protein carrier molecule
Are all ETCs the same?

Bacterial electron transport chains are
diverse

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Particular carriers and their order
Some bacteria may have several types of
electron transport chains
Eukaryotic electron transport chain is more
unified and better described
All have the same goal to capture energy
into ATP
The mitochondrial ETC


The enzyme complex NADH dehydrogenase starts the
process by dehydrogenating NADH and transferring its
high energy electrons to its coenzyme FMN
In turn the electrons are transferred down the chain from
FMN to Q to cytochrome b
 Electrons are then
passed from
cytochrome b to c1
to c to a and a3
with each
cytochrome
reduced as it gains
electrons and
oxidized as it loses
electrons
O2, the terminal electron acceptor

Finally, cytochrome a3 passes its electrons
to O2 which picks up protons to form H2O
How is ATP generated?

Electron transfer down the chain is accompanied
at several points by the active pumping of protons
across the inner mitochondrial membrane

This transfer of protons is used to generate ATP
by chemiosmosis as the protons move back
across the membrane
The ETC sets up a proton gradient

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As energetic electrons are passed down the ETC some
carriers (proton pumps) actively pump H+ across the
membrane.
Proton motive force results from an excess of protons
on one side of the membrane
Generation of ATP by chemiosmosis


Protons can only diffuse back along the gradient
through special protein channels that contain the
enzyme ATP synthase (Fo).
ATP synthase (Fo) uses
the energy released by
the diffusion of H+ across
the membrane to
synthesize ATP from
ADP
ETC drives chemiosmosis
NADH
FADH2
3 ATP
2 ATP
Aerobic Respiration

Complete oxidation of 1
glucose molecule
generates 38 ATP in
prokaryotes

2 from each of glycolysis
and 2 from the TCA cycle
by substrate level
phosphorylation

34 from oxidative
phosphorylation as a
result of 10 NADH and 2
FADH2 from glycolysis
and the TCA cycle
Anaerobic Respiration

Like aerobic respiration, it involves glycolysis, the
TCA cycle and an electron transport chain…. but,

The final electron acceptor is an inorganic molecule other
than O2
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Some bacteria use NO3- and produce either NO2-, N2O or N2
(Pseudomonas and Bacillus)
Desulfovibrio use SO42- to form H2S
Methanogens use carbonate to form methane
The amount of ATP generated varies with the pathway

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Only part of the TCA cycle operates under anaerobic conditions
Not all ETC carriers participate in anaerobic respiration
ATP yield never as high as aerobic respiration
Fermentation

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Uses Glycolysis but does not use the TCA cycle
or Electron Transport Chain
Releases energy from sugars or other organic
molecules, but only 2 ATP for each glucose
Does not use O2 o or inorganic electron acceptors
Uses an organic molecule as the final electron
acceptor
Produces only small amounts of ATP and most of
the energy remains in the organic end product
Fermentation

In fermentation, pyruvic acid or its
derivatives are reduced by NADH to
fermentation end products

Ensures recycling of NAD+ for glycolysis
Why bother with fermentation?

Fermenting bacteria can grow as fast as
those using aerobic respiration by
markedly increasing the rate of glycolysis

Fermentation permits independence from
molecular oxygen and allows colonization
of anaerobic environments
Types of fermentation
Acid Fermentation
Homolactic
 Only
lactic acid
 Streptococcus and
Lactobacillus
Heterolactic
 Mixture
of lactic acid,
acetic acid and CO2
 Can result in food
spoilage
 Can produce
 Yogurt
 Sauerkraut
 Pickles
Bring on the good stuff

Alcohol fermentation by the yeast
Saccharomyces is responsible for some of
the better things in life

CO2 produced causes bread to rise

Ethanol is used in alcoholic beverages
End products of fermentation
Metabolic pathways of Energy Use

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The complete oxidation of glucose to CO2
and H2O is considered an efficient process
But, 45% of the energy from glucose is
lost as heat
Cells use the remaining energy (in ATP) in
a variety of ways
E.g., active transport of molecules across
membrane or flagella motion
 Most is used for the production of new cellular
components

Integration of metabolic pathways

Carbohydrate catabolic pathways are central to
the supply of cellular energy

However, rather than being dead end pathways,
several intermediates in these pathways can be
diverted into anabolic pathways

This allows the cell to derive maximum benefit
from all nutrients and their metabolites

Amphibolic Pathways-integration of catabolic
and anabolic pathways to improve cell efficiency
Amphibolic view of metabolism
Glycolysis
glyceraldehyde3-phosphate
pyruvate
TCA cycle
acetyl-CoA
oxaloacetic acid
α-ketoglutaric
acid