Metabolism in cells can occur aerobically or anaerobically. Aerobic respiration uses oxygen as the terminal electron acceptor while anaerobic respiration uses molecules other than oxygen. Some microbes, called microaerophiles, grow best at low oxygen concentrations between 0-5%. Aerobic respiration involves glycolysis, the TCA cycle, and the electron transport chain to generate ATP. Anaerobic respiration and fermentation are used by microbes in low or no oxygen environments and can utilize nitrate, sulfate or carbon dioxide as terminal electron acceptors. Fermentation extracts energy from organic compounds without oxygen through pathways like lactic acid or alcoholic fermentation.
2. Metabolism
All chemical reactions involved in maintaining the
living state of the cells and the organism.
It is divided into two categories:
Catabolism - the breakdown of molecules to
obtain energy
Anabolism - the synthesis of all compounds
needed by the cells
2
3. Microorganisms can carry out respiratory
activities in different environments.
Aerobic respiration
Respiratory activity that uses oxygen as final
electron acceptor
Anaerobic respiration
Respiratory activity that uses molecules other
than oxygen as final electron acceptor.
Aerobic and Anaerobic Respiration
3
4. • A microorganism that requires free oxygen for growth
but at a lower concentration than that contained in the
atmosphere.
• Microaerophiles grow poorly at ambient (21% O2)
levels and therefore do not grow on the surface of
culture plates; they also grow poorly in anaerobic
conditions.
• Example:
Campylobacter jejuni grows optimally at 5% O2
Microaerophiles
4
5. Aerobic respiration
Similar to the aerobic respiration in plants.It involves
• Glycolysis
• TCA cycle
• Electron transport system to generate energy.
5
6. Glycolysis is the breakdown of glucose into
pyruate. It occurs in the cytoplasm of all the
microbes.
TCA Cycle is used to generate reducing
power(NADH) which generates ATP in the
Electron transport system.
Oxidation of pyuvate into CO2.
6
7. Electron transport chain (ETC) is a series of
compounds that transfer electrons from electron
donor to electron acceptor through redox
reactions, and couples the transfer of electrons
with proton transfer across the membrane.
7
9. Fermentation
• extracts energy from the oxidation of
organic compounds(carbohydrates)
• uses an endogenous electron acceptor.
• simple organic end products are formed.
• ATP is generated through the dehydrogenation
reactions.
9
10. Anaerobic Respiration
• Use Inorganic compounds as electron acceptors.
• Inorganic compounds have a lower reduction
potential than oxygen
• Many facultative anaerobes can use either
oxygen or alternative terminal electron acceptors
for respiration depending on the environmental
conditions.
10
11. Pathways for many forms of anaerobic
respiration are also known.
• Denitrification — nitrate as electron acceptor
• Sulfate reduction — sulfate as electron acceptor
• Acetogenesis — carbon dioxide as electron
acceptor
11
13. Function of Enzymes
Enzymes speed up the rate of chemical
reactions in the body by
• breaking down the components e.g.: starch
into maltose.
• building up reactions. e.g: amino acids into
proteins.
Enzymes lower the activation energy required
to start a chemical reaction
14. Characteristics of Enzymes
Enzymes are highly specific in action.
Enzymes remain chemically unchanged
at the end of the reaction.
Enzymes are required in minute amounts.
15. Mode of Action
Substrate fits in the enzyme active site, just like a
key fits into a lock.
An enzyme-substrate complex is formed.
Chemical reactions occur at the active site and
products are formed.
17. Temperature
With the increase in
temperature, the rate of enzyme
activity also increases until the
optimal temperature is
reached.
Further increase in
temperature, denatures the
enzyme and its activity declines.
18. pH
Enzyme works best within a narrow pH range
Each enzyme works best at particular pH, known
as its optimum pH level.
At extreme pH levels, enzymes lose their shape
and function and become denatured.
20. Inhibitors
Inhibitors slow down the rate of a reaction.
Sometimes necessory, otherwise undesirable.
There are two type of inhibitors:
•Competitive Inhibitors
•Non competitive inhibitors
21. Competitive inhibitor
fills the active site of an enzyme
compete with the normal substrate for
the active site
Non competitive inhibitors
do not compete with the substrate for
the enzyme’s active site
they interact with another part of the
enzyme
22. Anaerobic Respiration
• Respiration in which molecular oxygen is not cons
umed.
• Anaerobic respiration is a cellular respiration that
takes place without oxygen and begins the
breakdown process using electron acceptors and
instruments, but does not use oxygen.
• It takes place in cytoplasm
22
23. Electron Acceptors Other than oxygen
• Some microbes are capable of using nitrate as
their terminal electron accepter.
• If microbes have a choice, they will use oxygen
instead of nitrate, but in environments where
oxygen is limiting , they use nitrate.
• E.g. E. coli
23
24. Electron Acceptors Other than oxygen
• Several groups of microbes are capable of using
carbonate (CO2) as a terminal electron acceptor.
• Energy yields from CO2 reduction are low.
• E.g. Archaea
• Some Microbes also use Sulfate as a terminal
electron acceptor
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25. Glycolysis
• Metabolic pathway that converts glucose to
pyruvate
• Free energy released to form ATP and NADH
• Oxygen independent pathway
• Common to aerobic and anaerobic organisms
25
26. Glycolysis
• Occurs in cytosol of cell
• Embden–Meyerhof–Parnas (EMP pathway),
discovered by Gustav Embden, Otto Meyerhof,
and Jakub Karol Parnas
• The entire glycolysis pathway can be separated
into two phases:
- The Preparatory or Investment phase
- The Pay Off Phase
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32. Krebs Cycle
• Occurs in the mitochondrial matrix
• It is Amphibolic
• Acetyl CoA subunit combines with oxaloacetic
acid to form citric acid
• Citric acid enters the Krebs Cycle
• Through a series of reactions, citric acid is
converted to oxaloacetic acid to complete the
pathway
• Produces: GTP, 3 NADH, and 1 FADH2 , C02
• NADH and FADH2 transport electrons to ETC
33.
34. acetyl CoA oxaloacetate
CoASH
citrate synthase
citrate
OH2
CH3
C
O
SCoA
C O
CH2
C
O
C
OO
O
C
OO
CH2
C
CH2
C
OH C O
O
O O
+
Step 1: Formation of Citrate
36. isocitrate
NAD NADH CO2
isocitrate dehydrogenase
alpha ketoglutarate
C
OO
CH
CH
CH2
C
C O
O
OO
OH
C
OO
C
CH2
CH2
C
OO
O
Step 3. Oxidation of Isocitrate and
Formation of CO2
38. succinyl CoA
GDP GTP CoASH
succinate
succinyl CoA
synthetase
C
CH2
CH2
C
OO
OSCoA
C
CH2
CH2
C
OO
O
O
Step 5: Thioester bond cleavage in
Succinyl CoA and Phosphorylation of
GDP
42. Electron Transport Chain
• In prokaryotic cells, it is contained in the plasma
membrane.
• series of redox reactions
• transfer e- and H+ from NADH & FADH2 to O2
resulting in H2O
• O2 is considered the final electron acceptor
• As electrons are passed through the chain, there
occurs a step vise release of energy
43. Carrier molecules in ETS
• There are three classes of carrier molecules in
electron transport chains.
• Flavoproteins
• Cytochromes
• Coenzyme Q
45. Anaerobe
• Does not require oxygen for growth
• May react negatively or even die if oxygen is
present
• May be unicellular (e.g. protozoan , bacteria) or
multicellular
45
46. Types of Anaerobe
• Obligate anaerobes
• Microorganisms killed by
normal atmospheric concentrations
of oxygen (20.95% O2). Oxygen tolerance varies
between species, some capable of surviving in up
to 8% oxygen, others losing viability unless the
oxygen concentration is less than 0.5%
• E.g. Bactericides, Clostridium, Fusobacterium
46
47. Types of Anaerobe
• Aerotolerant Anaerobe
An aerotolerant anaerobe is an organism that
tolerates the presence of oxygen but does not
require it for growth. Instead, aerotolerant
anaerobes use fermentation to survive
E.g. Lactobacilli , Streptococci
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48. Types of Anaerobe
• Facultative anaerobes
A facultative anaerobe is an organism that
makes ATP by aerobic respiration if oxygen is
present, but is capable of switching
to fermentation or anaerobic respiration if oxygen
is absent.
E.g. Staphylococcus , Streptococcus , Listeria
48
49. How some Anaerobes are tolerant to
Oxygen
• Defense mechanisms possessed by bacteria against toxic
products of oxygen reduction.
The subsequent reaction between superoxide anions and the hydroxyl radical
results in the production of singlet oxygen which is also damaging to the cell
Superoxide anions can react with hydrogen peroxide in the cell to form hydroxyl
radicals
Many toxic by-products, including the superoxide anion and hydrogen peroxide,
are generated when molecular oxygen interacts with various cellular constituents
49
50. • The major enzymes present in aerobes that
protecting the cell against these toxic oxygen
reduction products are superoxide dismutase
(SOD), catalase, and peroxidases
50
51. Fermentation
• Metabolic process that converts sugar to
acids, gases, or alcohol.
• It occurs in yeast, bacteria and protozoan.
• Pyruvate made in glycolysis does not continue
through oxidation.
• NADH in glycolysis cannot drop its electrons
off there to turn back NAD+.
• Regenerate the electron carrier NAD+ from
NADH.
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52. Alcoholic fermentation
• Alcohol fermentation is
done by yeast and
some kinds of bacteria.
One glucose molecule
is converted into
two ethanol molecules
and two carbon
dioxide molecules:
C6H12O6 → 2 C2H5OH + 2
CO2
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53. Lactic acid fermentation
• It occurs in some kinds
of bacteria (such
as lactobacilli) and
some fungi.
• One molecule of
glucose (or any six-
carbon sugar) is
converted to two
molecules of lactic
acid:
C6H12O6 →
2CH3CHOHCOOH
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54. What about protozoa?
• Protozoa, principally ciliates, appear to contribute
considerably to the fermentation process.
• Several experiments have demonstrated that
lambs and calves deprived of their ruminal
protozoa show depressed growth rates compared
to controls with both bacteria and protozoa.
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55. Fungi have been employed
to break down cellulosic
wastes.
Acids and alcohols, are
inhibitory to the
common pathogenic
microorganisms
Microorganisms are
anabolic and
synthesize several
complex vitamins and
other growth factors.
Breaks down
indigestible coatings
and cell walls both
chemically and
physically.
Alcohols and acids inhibit
many proteolytic and
lipolytic organisms that are
capable of food spoilage if
not controlled.
Fermentation is the
main source of ethanol
in the production
of ethanol fuel.
Sewage is
digested by
enzymes
secreted by
bacteria.
Foods as diverse as yogurt,
hard sausages, and
sauerkraut all contain acid.
IMPORTANCE
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