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Chapter 10
Catabolism: Energy
Release and
Conservation
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Microbial Metabolism
A. Basic
Concepts of Metabolism
B. Glycolytic Pathways
C. Fermentation
D. Respiration
E. Photosynthesis
F. Chemolithotrophy
G. The Nitrogen Cycle
Recap … Metabolism
Anabolism and catabolism are intimately linked
by energy coupling

Energy coupling means that the energy
“generated” by catabolic processes is harnessed
by cells to perform anabolic processes
 “The metabolic pathways intersect in such a way
that energy released from the ‘downhill’
reactions of catabolism can be used to drive the
'uphill' reactions of the anabolic pathways. This
transfer of energy from catabolism to anabolism
is called energy coupling.”


Exergonic reaction
Exergonic reaction
 An exergonic reaction net-generates
(gives off) energy (e.g., heat)

That is, the products of such a reaction
possess less stored energy than do the
reactants
Endergonic reaction
Endergonic reaction
An endergonic reaction is one that
requires a net input of energy in order to
proceed
 The products of endergonic reactions
possess more energy than do the
reactant

..REDOX
Reduction and Oxidation
Reduction and oxidation always occur together.
In a reduction-oxidation reaction (redox
reaction), one substance gets reduced, and
another substance gets oxidized.
The thing that gets oxidized is called the
electron donor, and the thing that gets
reduced is called the electron acceptor.
…Catabolism
Chemoorganotrophs
 Animals and many microorganisms are
Chemoorganotrophs i.e use of organic
molecules as the source of energy.
 Molecules that supplies them with energy
also supplies them with carbon and
electrons
..catabolism

Chemoheteroptrophs also referred as
Chemoorganotrophs can use one or more of the
following catabolism:

Aerobic respiration

Anaerobic Respiration or Fermentation
Chemoorganic Fueling Processes
−E.g Respiration
Most respiration involves use of an electron
transport chain which uses exogenous
electron acceptor
 Aerobic respiration
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Anaerobic respiration
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final electron acceptor is oxygen
final electron acceptor such as NO3-, SO42-, CO2,
etc.
In respiration, as electrons pass through the
electron transport chain to the final electron
acceptor, a proton motive force
(PMF)/potential energy is generated and
used to synthesize ATP from ADP and P
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Chemoorganic Fueling
Processes −E.g Fermentation
Whereas, fermentation, uses an endogenous
(from within the cells) electron acceptor
 usually
an intermediate of the pathway used
to oxidize the organic energy source (e.g.,
pyruvate)
Does not involve the use of an electron
transport chain nor the generation of a
proton motive force/potential energy
 ATP synthesized only by substrate-level
phosphorylation

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10
Glycolytic pathways
Four major glycolytic pathways found in different
bacteria:
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Embden-Meyerhoff-Parnas pathway
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Hexose monophosphate pathway/Pentose Phosphate
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Also found in most organisms
Responsible for synthesis of pentose sugars used in
nucleotide synthesis
Entner-Doudoroff pathway
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“Classic” glycolysis
Found in almost all organisms
Found in Pseudomonas and related genera
Phosphoketolase pathway

Found in Bifidobacterium and Leuconostoc
Fermentation
Pyruvic acid is reduced to form organic acids or
alcohols.
Examples of fermentation pathways
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Lactic acid fermentation
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Mixed acid fermentation
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Found in many bacteria;
e.g. Streptococcus cremoris, Lactobacillus acidophilus
e.g. Escherichia coli
Basis of the methyl red test
2,3-Butanediol fermentation
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
e.g. Enterobacter aerogenes
Basis of the Voges-Proskauer reaction
…Fermentation
Respiration

Cellular respiration is a series of chemical
and physical processes which together
serve to remove potential energy
containing electrons from organic
compounds, use the energy thus liberated
to generate ATP and then donate these
now energy-spent electrons to oxygen
…Respiration
Glucose is oxidized and releases its
electrons during cell respiration (electrons
associated with H atoms).Sugar gets
oxidized (electrons taken off) and oxygen
gets reduced (takes electrons)
 Overall reaction (oxidation of
glucose):
C6H12O6 + 6O2 (oxygen required) ---> 6CO2 +6H2O + energy + heat
Delta G = -686kcal/mol

…Respiration
Majority of energy (90%) is generated by
electron transport chain on inner
membrane of mitochondria (oxidative
phosphorylation).
 Small amount of energy created by
phosphorylation of ADP during Glycolysis
and Krebs cycle

The steps of Cellular
respiration
Respiration includes
 Glycolysis,
 Krebs Cycle (TCA or Citric Acid Cycle), and
 Electron transport chain
The steps of Cellular
respiration

A. Glycolysis (glyco =sugar, lysis = break)

Initial breakdown of glucose
B. The Krebs cycle /(TCA or Citric Acid Cycle),
Further breakdown of glucose yielding electrons and
CO2
 C. The electron transport chain.
where electrons taken from glucose during glycolysis and
Krebs cycle are taken;where most of the ATP is finally
re-made.
The Tricarboxylic Acid Cycle
also called citric acid cycle and Kreb’s
cycle
 common in aerobic bacteria, free-living
protozoa, most algae, and fungi

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2.Located in the inner membrane of the mitochondrion.
3. Electrons are passed down the electron chain, along the energy gradient, to oxygen
Figure 10.8
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Glycolysis
A. Glycolysis (splitting of sugar) occurs in
cytoplasm-end product is pyruvate.
 Pathway has ten steps: first five steps are energy
investment, final five steps yield energy.
 As glucose is oxidized and broken down NAD+ is
reduced to NADH (electron carrier).
 Glycolysis occurs whether or not O2 is present.
 Glycolysis which occurs in the absence of O2 is
termed fermentation.
 In the presence of O2, NADH is passed on to the
electron transport chain and pyruvate is passed
into the Krebs Cycle.
...Glycolisis Overview
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1. glucose is split into 2 (3C)(Pyruvic acid molecules)
sugars
2. the 3C sugars are oxidized and rearranged to produce
pyruvate.
3. the oxidation is coupled with NAD+ being reduced to
NADH.
4. consists of 2 phases
a.energy investment phase (using 2 ATPs
per glucose molecule)
b. energy yielding phase (making 4 ATPs
per glucose molecule via substrate-level
phosphorylation.)
…Glycolysis Overview
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5. other interesting facts about glycolysis:
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a. occurs in cytosol (ground substance of cell)
b. anaerobic (does not need O2,not really a part
of respiration).
c. Pyruvate enters the mitochondrion through a
transport protein.
…. GLYCOLYSIS Overview
Glucose molecule in the cytosol 2 pyruvic acid molecules (3
carbons), 4 ATP formed (2 ATP used up), 2 NADH/glucose
formed.
Pyruvic acid & NADH enter mitochondria
The First Stage of Glycolysis
Glucose (6C is broken down into 2 PGAL's (Phosphoglyceraldehyde - 3Carbon
molecules)
This requires two ATP's
The Second Stage of Glycolysis
2 PGAL's (3C) are converted to 2 pyruvates
This creates 4 ATP's and 2 NADH's
The net ATP production of Glycolysis is 2 ATP's
Formation of acetyl CoA
B. Formation of acetyl CoA
1. Intermediate stage between glycolysis and Krebs
Cycle.
 2. The oxidation of 3C pyruvate to 2C acetyl CoA (with
the loss of CO2) coupled with the reduction of NAD+ to
NADH.

..Formation of acetyl CoA
The Oxidation of Pyruvate to form Acetyl CoA for Entry Into
the Krebs Cycle
•2 NADH's are generated (1 per pyruvate)
•2 CO2 are released (1 per pyruvate)
Kreb Cycle

Preliminary step is conversion of pyruvate to acetyl CoA.
catalyzed by pyruvate dehydrogenase complex (complex
of three enzymes) and byproducts of conversion to
acetyl CoA are CO2 and NADH.
There are eight steps in pathway in the Kreb Cycle
 Initial step is condensation of acetyl CoA with
oxaloacetate and final step which completes the cycle is
the decomposition of citrate back to oxaloacetate.
Steps in Kreb Cycle
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Step 1: The unstable bond of acetyl CoA breaks, and
the two-carbon acetyl group bonds to the four-carbon
oxaloacetate to form six-carbon citrate.
Step 2: Citrate is isomerized to isocitrate.
Step 3: Two major events occur during this step:
-Isocitrate loses CO2 leaving a five-carbon molecule.
-The five-carbon compound is oxidized and NAD+ is
reduced.
..Steps in Kreb Cycle
Step 4: A multi enzyme complex catalyzes:
- Removal of CO2
- Oxidation of the remaining four-carbon
compound and reduction of NAD+
- Attachment of CoA with a high energy
bond to form succinyl CoA.
..Steps in Kreb Cycle
Step 5: Substrate-level phosphorylation occurs in a
series of enzyme catalyzed reactions:
-The high energy bond of succinyl CoA breaks, and
some energy is conserved as CoA is displaced by a
phosphate group.
-The phosphate group is transferred to GDP to form GTP
(Guanosine triphospahte) and succinate.
GTP donates a phosphate group to ADP to form ATP.
Step 6: Succinate is oxidized to fumarate and FAD is
reduced.
- Two hydrogens are transferred to FAD to form FADH2.
- The dehydrogenase that catalyzes this reaction is
bound to the inner mitochondrial membrane.

..Steps in Kreb Cycle
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Step 7: Water is added to fumarate which
rearranges its chemical bonds to form malate
..Steps in Kreb Cycle
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Step 8: Malate is oxidized and NAD+ is reduced.
-A molecule of NADH is produced.
-Oxaloacetate is regenerated to begin the Kreb cycle
again.
-Two turns of the Krebs cycle produce two ATPs by
substrate-level phosphorylation.
-ATP output of respiration results from oxidative
phosphorylation.
- Reduced coenzymes produced by the Krebs cycle (six
NADH and two FADH2 per glucose) carry high energy
electrons to the electron transport chain.
- The ETC couples electron flow down the chain to ATP
synthesis.
Figure 10.8-Tri carboxylic Acid Cycle
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Net Energy Gained
Summary of the net energy yield :

From glycolysis : 2ATP + 2 NADH
From matrix reaction : 2 NADH
From Kreb cycle : 2 ATP + 6 NADH + 2 FADH2
Total : 4 ATP + 10 NADH + 2 FADH2
 Most of the energy that has been released has been
captured in the form of electron transport molecules.
malate. NAD binds to malate and leaves as NADH which creates a new oxaloacetate molec
.
Electron transport chain
C. Electron transport chain:
• Located on inner membrane of mitochondria.
•Composed of three protein complexes in the
membrane and two mobile electron carriers
(Ubiquinone, Cytochromes).
• Electrons passed down chain in series of reductions
and oxidation reactions.
•Each successive complex has a higher affinity for
the electrons.
•Oxygen is the ultimate electron acceptor . As
electrons are passed along chain, hydrogen (H+)
atoms are pumped from the matrix to the inner
membrane space of mitochondria.
• Exergonic energy created by electron flow powers
H+ pumps.
The Electron Transport Chain
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Utilizes NADH and FADH2 formed in the previous
steps (kreb’s cycle)
Series of electron carriers that operate together to
transfer electrons from NADH and FADH2 to a
terminal electron acceptor
Movement of H+ ions down concentration gradient
provides energy to make ATP from ADP and P
catalyzed by ATP synthase, an integral membrane
protein. It is not known exactly how the ATP
synthase using the downhill H+ current to attach
inorganic phosphate to ADP.
Electrons flow from carriers with more negative E0
(reduction potential) to carriers with more positive E0
As electrons transferred, energy released.
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-Large difference in
E0 (reduction potential)
of NADH and
E0 of O2 (1.14 Volt)
-Hence large
amount of
energy released
For ATP production
Figure 10.9-ETC
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49
..ETC
•to break down NADH and FADH2, pumping H+ into the outer compartment of the
mitochondria .
•In this reaction, the ETS creates a gradient which is used to produce ATP
•Electron Transport Phosphorylation typically produces 32 ATP's
•ATP is generated as H+ moves down its concentration gradient through a special
enzyme called ATP Synthetase
….ETS
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Oxygen is the ultimate electron acceptor . As electrons
are passed along chain, hydrogen (H+) atoms are
pumped from the matrix to the inner membrane space of
mitochondria.
Exergonic energy created by electron flow powers H+
pumps.
Metabolic water
Metabolic water
•Along with two electrons, at the end of the ETS each oxygen atom also is combined
with two hydrogen ions
•The net result is water (i.e., 2e- + 2H+ + ½O2  H2O)
•This water is termed metabolic (as in, metabolic water)
•Thus, one of the products of the complete oxidation of glucose is water & Energy
Figure out How?????
•ATP yield (36-38 ATP per molecule of glucose),How?
34 ATP produced by chemiosmotic synthesis (electron transport)
4 ATP produced directly: (2 ATP from glycolysis
2 ATP from citric acid cycle)
38 ATP theoretical maximum gross yield from the complete oxidation
(-2 ATP required for active transport of NADH from glycolysis into the mitoch
in some cells)
36-38 ATP net yield from one glucose molecule
Oxidative Phosphorylation

process by which ATP is synthesized as the result of
electron transport driven by the oxidation of a
chemical energy source
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Oxidative phosphorylation
•Oxidative phosphorylation is the phosphorylation of ADP using a mechanism
powered by reduced electrons which, once their potential energy has been removed, are
ultimately donated to atoms of oxygen
•Substrate-level phosphorylation
Substrate-level phosphorylation is the donation of a phosphate directly to
ADP from a phosphorylated organic intermediate
Phototrophy

photosynthesis
 energy
from light trapped and converted to
chemical energy
 a two part process
 light
reactions in which light energy is trapped and
converted to chemical energy
 dark reactions in which the energy produced in the
light reactions is used to reduce CO2 and
synthesize cell constituents
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Bibliography
Lecture PowerPoints Prescott’s Principles of
Microbiology-Mc Graw Hill Co.
 http://en.wikipedia.org/wiki/Scientific_metho
d
 https://files.kennesaw.edu/faculty/jhendrix/bi
o3340/home.html


http://hyperphysics.phyastr.gsu.edu/Hbase/biology/atp.html
http://www.uic.edu/classes/bios/bios100/l
ecturesf04am/lect12.htm
 http://www.uic.edu/classes/bios/bios100/s
ummer2003/krebsfull.htm
 http://www.nileshs.k12.il.us/jacnau/chpt9.html#Krebs%20
Cycle
